text:
Copyright © 1995-2014 The FreeBSD Documentation Project
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This is the FAQ for FreeBSD versions 8.X
. Every effort has been made to make this FAQ as
informative as possible; if you have any suggestions as to how
it may be improved, please feel free to mail them to the
FreeBSD documentation project mailing list.
The latest version of this document is always available from the FreeBSD website. It may also be downloaded as one large HTML file with HTTP or as a variety of other formats from the FreeBSD FTP server.
1.1. | What is FreeBSD? |
FreeBSD is a modern operating system for desktops, laptops, servers, and embedded systems with support for a large number of platforms. It is based on U.C. Berkeley's "4.4BSD-Lite" release, with some "4.4BSD-Lite2" enhancements. It is also based indirectly on William Jolitz's port of U.C. Berkeley's "Net/2" to the i386™, known as "386BSD", though very little of the 386BSD code remains. FreeBSD is used by companies, Internet Service Providers, researchers, computer professionals, students and home users all over the world in their work, education and recreation. For more detailed information on FreeBSD, please see the FreeBSD Handbook. | |
1.2. | What is the goal of the FreeBSD Project? |
The goal of the FreeBSD Project is to provide a stable and fast general purpose operating system that may be used for any purpose without strings attached. | |
1.3. | Does the FreeBSD license have any restrictions? |
Yes. Those restrictions do not control how you use the code, merely how you treat the FreeBSD Project itself. If you have serious license concerns, read the actual license. For the simply curious, the license can be summarized like this.
Many of us have a significant investment in the project and would certainly not mind a little financial compensation now and then, but we definitely do not insist on it. We believe that our first and foremost "mission" is to provide code to any and all comers, and for whatever purpose, so that the code gets the widest possible use and provides the widest possible benefit. This, we believe, is one of the most fundamental goals of Free Software and one that we enthusiastically support. Code in our source tree which falls under the GNU General Public License (GPL) or GNU Library General Public License (LGPL) comes with slightly more strings attached, though at least on the side of enforced access rather than the usual opposite. Due to the additional complexities that can evolve in the commercial use of GPL software, we do, however, endeavor to replace such software with submissions under the more relaxed FreeBSD license whenever possible. | |
1.4. | Can FreeBSD replace my current operating system? |
For most people, yes. But this question is not quite that cut-and-dried. Most people do not actually use an operating system. They use applications. The applications are what really use the operating system. FreeBSD is designed to provide a robust and full-featured environment for applications. It supports a wide variety of web browsers, office suites, email readers, graphics programs, programming environments, network servers, and just about everything else you might want. Most of these applications can be managed through the Ports Collection. If you need to use an application that is only available on one operating system, you simply cannot replace that operating system. Chances are there is a very similar application on FreeBSD, however. If you want a solid office or Internet server, a reliable workstation, or just the ability to do your job without interruptions, FreeBSD will almost certainly do everything you need. Many computer users across the world, including both novices and experienced UNIX® administrators, use FreeBSD as their only desktop operating system. If you are migrating to FreeBSD from some other UNIX® environment, you already know most of what you need to. If your background is in graphic-driven operating systems such as Windows® and Mac OS®, you may be interested in using PC-BSD, a FreeBSD based distribution, instead. If you have not used UNIX® before expect to invest additional time learning the UNIX® way of doing things. This FAQ and the FreeBSD Handbook are excellent places to start. | |
1.5. | Why is it called FreeBSD? |
It is worth pointing out that the word "free" is being used in two ways here, one meaning "at no cost", the other meaning "you can do whatever you like". Apart from one or two things you cannot do with the FreeBSD code, for example pretending you wrote it, you can really do whatever you like with it. | |
1.6. | What are the differences between FreeBSD and NetBSD, OpenBSD, and other open source BSD operating systems? |
James Howard wrote a good explanation of the history and differences between the various projects, called The BSD Family Tree which goes a fair way to answering this question. Some of the information is out of date, but the history portion in particular remains accurate. Most of the BSDs share patches and code, even today. All of the BSDs have common ancestry. The design goals of FreeBSD are described in Q: 1.2, above. The design goals of the other most popular BSDs may be summarized as follows:
| |
1.7. | What is the latest version of FreeBSD? |
At any point in the development of FreeBSD, there can be
multiple parallel branches. 10. Up until the release of 9.0, the
9. Version 9.2 is the latest release from the 10-STABLE branch; it was released in September 2013. Version 8.4 is the latest release from the 9-STABLE branch; it was released in June 2013. Briefly, -STABLE is aimed at the ISP, corporate user, or any user who wants stability and a minimal number of changes compared to the new (and possibly unstable) features of the latest -CURRENT snapshot. Releases can come from either branch, but -CURRENT should only be used if you are prepared for its increased volatility (relative to -STABLE, that is). Releases are made every few months. While many people stay more up-to-date with the FreeBSD sources (see the questions on FreeBSD-CURRENT and FreeBSD-STABLE) than that, doing so is more of a commitment, as the sources are a moving target. More information on FreeBSD releases can be found on the Release Engineering page and in release(7). | |
1.8. | What is FreeBSD-CURRENT? |
FreeBSD-CURRENT is the development version of the operating system, which will in due course become the new FreeBSD-STABLE branch. As such, it is really only of interest to developers working on the system and die-hard hobbyists. See the relevant section in the Handbook for details on running -CURRENT. If you are not familiar with FreeBSD you should not use FreeBSD-CURRENT. This branch sometimes evolves quite quickly and due to mistake can be un-buildable at times. People that use FreeBSD-CURRENT are expected to be able to analyze, debug, and report problems. FreeBSD snapshot releases are made based on the current state of the -CURRENT and -STABLE branches. The goals behind each snapshot release are:
No claims are made that any -CURRENT snapshot can be considered "production quality" for any purpose. If you want to run a stable and fully tested system, you will have to stick to full releases, or use the -STABLE snapshots. Snapshot releases are directly available from snapshot. Official snapshots are generated on a regular basis for all actively developed branches. | |
1.9. | What is the FreeBSD-STABLE concept? |
Back when FreeBSD 2.0.5 was released, FreeBSD development branched in two. One branch was named -STABLE, one -CURRENT. FreeBSD-STABLE is intended for Internet Service Providers and other commercial enterprises for whom sudden shifts or experimental features are quite undesirable. It receives only well-tested bug fixes and other small incremental enhancements. FreeBSD-CURRENT, on the other hand, has been one unbroken line since 2.0 was released, leading towards 9.2-RELEASE and beyond. For more detailed information on branches see "FreeBSD Release Engineering: Creating the Release Branch", the status of the branches and the upcoming release schedule can be found on the Release Engineering Information page. 9.2-STABLE is the actively developed -STABLE branch. The latest release on the 9.2-STABLE branch is 9.2-RELEASE, which was released in September 2013. The 11-CURRENT branch is the actively developed -CURRENT branch toward the next generation of FreeBSD. See What is FreeBSD-CURRENT? for more information on this branch. | |
1.10. | When are FreeBSD releases made? |
The Release Engineering Team More information on the release engineering process (including a schedule of upcoming releases) can be found on the release engineering pages on the FreeBSD Web site. For people who need or want a little more excitement, binary snapshots are made weekly as discussed above. | |
1.11. | Who is responsible for FreeBSD? |
The key decisions concerning the FreeBSD project, such as the overall direction of the project and who is allowed to add code to the source tree, are made by a core team of 9 people. There is a much larger team of more than 350 committers who are authorized to make changes directly to the FreeBSD source tree. However, most non-trivial changes are discussed in advance in the mailing lists, and there are no restrictions on who may take part in the discussion. | |
1.12. | Where can I get FreeBSD? |
Every significant release of FreeBSD is available via anonymous FTP from the FreeBSD FTP site:
Information about obtaining FreeBSD on CD, DVD, and other media can be found in the Handbook. | |
1.13. | How do I access the Problem Report database? |
The Problem Report database of all user change requests may be queried by using our web-based PR query interface. The send-pr(1) command can be used to submit problem reports and change requests via electronic mail. Alternatively, the web-based problem report submission interface can be used to submit problem reports through a web browser. Before submitting a problem report, please read Writing FreeBSD Problem Reports, an article on how to write good problem reports. |
2.1. | What good books are there about FreeBSD? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The project produces a wide range of documentation,
available online from this link: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2.2. | Is the documentation available in other formats, such as plain text (ASCII), or PostScript®? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Yes. The documentation is available in a number of different formats and compression schemes on the FreeBSD FTP site, in the /pub/FreeBSD/doc/ directory. The documentation is categorized in a number of different ways. These include:
After choosing the format and compression mechanism that you want to download, you will have to download the compressed files yourself, uncompress them, and then copy the appropriate documents into place. For example, the split HTML version of the FAQ,
compressed using bzip2(1), can be found in
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/en_US.ISO8859-1/books/faq/book.html-split.tar.bz2# tar xvf book.html-split.tar.bz2 If the file is compressed,
tar will automatically
detect the appropriate format and decompress it correctly.
You will be left with a collection of
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2.3. | Where do I find info on the FreeBSD mailing lists? What FreeBSD news groups are available? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
You can find full information in the Handbook entry on mailing-lists and the Handbook entry on newsgroups. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2.4. | Are there FreeBSD IRC (Internet Relay Chat) channels? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Yes, most major IRC networks host a FreeBSD chat channel:
The FreeBSD wiki has a good list of IRC channels. Each of these channels are distinct and are not connected to each other. Their chat styles also differ, so you may need to try each to find one suited to your chat style. As with all types of IRC traffic, if you are easily offended or cannot deal with lots of young people (and more than a few older ones) doing the verbal equivalent of jello wrestling, do not even bother with it. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2.5. | Are there any web based forums to discuss FreeBSD? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The official FreeBSD forums are located at http://forums.FreeBSD.org/. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2.6. | Where can I get commercial FreeBSD training and support? | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
iXsystems, Inc., parent company of the FreeBSD Mall, provides commercial FreeBSD and PC-BSD software support, in addition to FreeBSD development and tuning solutions. BSD Certification Group, Inc. provides system administration certifications for DragonFly BSD, FreeBSD, NetBSD, OpenBSD. If you are interested in them, visit their site. Any other organizations providing training and support should contact the Project to be listed here. |
3.1. | Which platform should I download? I have a 64
bit capable Intel® CPU,
but I only see | ||||||||||
amd64 is the term FreeBSD uses for 64-bit compatible x86 architectures (also known as "x86-64" or "x64"). Most modern computers should use amd64. Older hardware should use i386. If you are installing on a non-x86-compatible architecture select the platform which best matches the architecture you are using. | |||||||||||
3.2. | Which file do I download to get FreeBSD? | ||||||||||
On the
Getting FreeBSD
page select Any of the following can be used:
pc98 users require these floppy images:
Full instructions on this procedure and a little bit more about installation issues in general can be found in the Handbook entry on installing FreeBSD. | |||||||||||
3.3. | What do I do if the images do not fit on a single disk? | ||||||||||
Common mistakes when preparing the boot media are:
| |||||||||||
3.4. | Where are the instructions for installing FreeBSD? | ||||||||||
Installation instructions for versions since FreeBSD 9.0 can be found at Handbook entry on installing FreeBSD. Older instructions can be found in the legacy entry on installing FreeBSD. | |||||||||||
3.5. | What do I need to run FreeBSD? | ||||||||||
For FreeBSD you will need a 486 or better PC, with 64 MB or more of RAM and at least 1 GB of hard disk space. See also Chapter 4, Hardware Compatibility. | |||||||||||
3.6. | How can I make my own custom release or install disk? | ||||||||||
Customized FreeBSD installation media can be created by building a custom release. Follow the instructions in the Release Engineering article. | |||||||||||
3.7. | Can Windows® co-exist with FreeBSD? | ||||||||||
If Windows® is installed first, then yes. FreeBSD's boot manager will then manage to boot Windows® and FreeBSD. If you install Windows® second, it will boorishly overwrite your boot manager without even asking. If that happens, see the next section. | |||||||||||
3.8. | Another operating system destroyed my Boot Manager. How do I get it back? | ||||||||||
This depends on what boot manager you have installed.
The FreeBSD boot selection menu (likely what you are using
if you end up in this situation) can be reinstalled using
boot0cfg(8). For example, to restore the boot menu
onto the disk # boot0cfg -B ada0 The non-interactive MBR bootloader can be installed using gpart(8): # gpart bootcode -b /boot/mbr ada0 For more complex situations, including GPT disks, see gpart(8). | |||||||||||
3.9. | I booted from my ATAPI CD-ROM, but the install program says no CD-ROM is found. Where did it go? | ||||||||||
The usual cause of this problem is a mis-configured CD-ROM drive. Many PCs now ship with the CD-ROM as the slave device on the secondary IDE controller, with no master device on that controller. This is illegal according to the ATAPI specification, but Windows® plays fast and loose with the specification, and the BIOS ignores it when booting. This is why the BIOS was able to see the CD-ROM to boot from it, but why FreeBSD cannot see it to complete the install. Reconfigure your system so that the CD-ROM is either the master device on the IDE controller it is attached to, or make sure that it is the slave on an IDE controller that also has a master device. | |||||||||||
3.10. | Do I need to install the source? | ||||||||||
In general, no. There is nothing in the base system which requires the presence of the source to operate. Some ports, like sysutils/lsof, will not build unless the source is installed. In particular, if the port builds a kernel module or directly operates on kernel structures, the source must be installed. | |||||||||||
3.11. | Do I need to build a kernel? | ||||||||||
Usually not. The supplied | |||||||||||
3.12. | Should I use DES, Blowfish, or MD5 passwords and how do I specify which form my users receive? | ||||||||||
FreeBSD 7 and 8 use MD5 password hashing by
default. Recent versions
of FreeBSD use SHA512 by default.
These are
believed to be more secure than the traditional UNIX®
password format, which used a scheme based on the
DES algorithm. DES passwords are still
available if you need to share your password file with
legacy operating systems which still use the less secure
password format. FreeBSD also allows you to use the Blowfish
and MD5 password formats. Which password
format to use for new passwords is controlled by the
| |||||||||||
3.13. | What are the limits for memory? | ||||||||||
Memory limits depend on the platform used. On a standard i386™ install, the limit is 4 GB but more memory can be supported through pae(4). See instructions for using 4 GB or more memory on i386™. FreeBSD/pc98 has a limit of 4 GB memory, and PAE can not be used with it. Other architectures supported by FreeBSD have much higher theoretical limits on maximum memory (many terabytes). | |||||||||||
3.14. | What are the limits for FFS file systems? | ||||||||||
For FFS file systems, the largest file system is practically limited by the amount of memory required to fsck(8) the file system. fsck(8) requires one bit per fragment, which with the default fragment size of 4 KB equates to 32 MB of memory per TB of disk. This does mean that on architectures which limit userland processes to 2 GB (e.g., i386™), the maximum fsck(8)'able filesystem is ~60 TB. If there was not a fsck(8) memory limit the maximum filesystem size would be 2 ^ 64 (blocks) * 32 KB => 16 Exa * 32 KB => 512 ZettaBytes. The maximum size of a single FFS file is approximately 2 PB with the default block size of 32 KB. Each 32 KB block can point to 4096 blocks. With triple indirect blocks, the calculation is 32 KB * 12 + 32 KB * 4096 + 32 KB * 4096^2 + 32 KB * 4096^3. Increasing the block size to 64 KB will increase the max file size by a factor of 16. | |||||||||||
3.15. | Why do I get an error message, readin failed after compiling and booting a new kernel? | ||||||||||
Because your world and kernel are out of sync. This is
not supported. Be sure you use You can boot by specifying the kernel directly at the
second stage, pressing any key when the | |||||||||||
3.16. | Is there a tool to perform post-installation configuration tasks? | ||||||||||
Yes, head/ users can set
4.1.1. | I want to get a piece of hardware for my FreeBSD system. Which model/brand/type is best? |
This is discussed continually on the FreeBSD mailing lists. Since hardware changes so quickly, however, we expect this. We still strongly recommend that you read through the Hardware Notes for FreeBSD 9.2 or 8.4 and search the mailing list archives before asking about the latest and greatest hardware. Chances are a discussion about the type of hardware you are looking for took place just last week. If you are looking for a laptop, check the FreeBSD laptop computer mailing list archives. Otherwise, you probably want the archives for the FreeBSD general questions mailing list, or possibly a specific mailing list for a particular hardware type. | |
4.1.2. | Does FreeBSD support more than 4 GB of memory (RAM)? More than 16 GB? More than 48 GB? |
Yes. FreeBSD as an operating system generally supports as much physical memory (RAM) as the platform it is running on does. Keep in mind that different platforms have different limits for memory; for example i386™ without PAE supports at most 4 GB of memory (and usually less than that because of PCI address space) and i386™ with PAE supports at most 64 GB memory. AMD64 platforms currently deployed support up to 1 TB of physical memory. | |
4.1.3. | Why does FreeBSD report less than 4 GB memory when installed on an i386™ machine? |
The total address space on i386™ machines is 32-bit, meaning that at most 4 GB of memory is addressable (can be accessed). Furthermore, some addresses in this range are reserved by hardware for different purposes, for example for using and controlling PCI devices, for accessing video memory, and so on. Therefore, the total amount of memory usable by the operating system for its kernel and applications is limited to significantly less than 4 GB. Usually, 3.2 GB to 3.7 GB is the maximum usable physical memory in this configuration. To access more than 3.2 GB to 3.7 GB of installed memory (meaning up to 4 GB but also more than 4 GB), a special tweak called PAE must be used. PAE stands for Physical Address Extension and is a way for 32-bit x86 CPUs to address more than 4 GB of memory. It remaps the memory that would otherwise be overlaid by address reservations for hardware devices above the 4 GB range and uses it as additional physical memory (see pae(4)). Using PAE has some drawbacks; this mode of memory access is a little bit slower than the normal (without PAE) mode and loadable modules (see kld(4)) are not supported. This means all drivers must be compiled into the kernel. The most common way to enable PAE is to build a new
kernel with the special ready-provided kernel configuration
file called options PAE PAE is not much used nowadays because most new x86 hardware also supports running in 64-bit mode, known as AMD64 or Intel® 64. It has a much larger address space and does not need such tweaks. FreeBSD supports AMD64 and it is recommended that this version of FreeBSD be used instead of the i386™ version if 4 GB or more memory is required. |
4.2.1. | Does FreeBSD support architectures other than the x86? |
Yes. FreeBSD divides support into multiple tiers. Tier 1 architectures, such as i386 or amd64; are fully supported. Tiers 2 and 3 are supported on an if-possible basis. A full explanation of the tier system is available in the Committer's Guide. A complete list of supported architectures can be found on the platforms page. | |
4.2.2. | Does FreeBSD support Symmetric Multiprocessing (SMP)? |
FreeBSD supports symmetric multi-processor (SMP) on all non-embedded platforms (e.g, i386, amd64, etc.). SMP is also supported in arm and MIPS kernels, although some CPUs may not support this. FreeBSD's SMP implementation uses fine-grained locking, and performance scales nearly linearly with number of CPUs. smp(4) has more details. | |
4.2.3. | What is microcode? How do I install Intel® CPU microcode updates? |
Microcode is a method of programmatically implementing hardware level instructions. This allows for CPU bugs to be fixed without replacing the on board chip. Install sysutils/devcpu-data, then add: microcode_update_enable="YES" to |
4.3.1. | What kind of hard drives does FreeBSD support? |
FreeBSD supports EIDE, SATA, SCSI, and SAS drives (with a compatible controller; see the next section), and all drives using the original "Western Digital" interface (MFM, RLL, ESDI, and of course IDE). A few ESDI controllers that use proprietary interfaces may not work: stick to WD1002/3/6/7 interfaces and clones. | |
4.3.2. | Which SCSI or SAS controllers are supported? |
See the complete list in the Hardware Notes for FreeBSD 9.2 or 8.4. | |
4.3.3. | What types of tape drives are supported? |
FreeBSD supports all standard SCSI tape interfaces. | |
4.3.4. | Does FreeBSD support tape changers? |
FreeBSD supports SCSI changers using the ch(4) device and the chio(1) command. The details of how you actually control the changer can be found in the chio(1) manual page. If you are not using AMANDA or some other product that already understands changers, remember that they only know how to move a tape from one point to another, so you need to keep track of which slot a tape is in, and which slot the tape currently in the drive needs to go back to. | |
4.3.5. | Which CD-ROM drives are supported by FreeBSD? |
Any SCSI drive connected to a supported controller is supported. Most ATAPI compatible IDE CD-ROMs are supported. | |
4.3.6. | Which CD-RW drives are supported by FreeBSD? |
FreeBSD supports any ATAPI-compatible IDE CD-R or CD-RW drive. See burncd(8) for details. FreeBSD also supports any SCSI CD-R or CD-RW drives.
Install and use |
4.4.1. | Is it possible to use a mouse in any way outside the X Window system? |
If you are using the default console driver, syscons(4), you can use a mouse pointer in text consoles to cut & paste text. Run the mouse daemon, moused(8), and turn on the mouse pointer in the virtual console: # moused -p /dev/xxxx -t yyyy# vidcontrol -m on Where If you have a PS/2 mouse, just add
When the mouse daemon is running, access to the mouse must be coordinated between the mouse daemon and other programs such as X Windows. Refer to the FAQ Why does my mouse not work with X? for more details on this issue. | |
4.4.2. | How do I cut and paste text with a mouse in the text console? |
It is not possible to remove data using the mouse. However, it is possible to "copy and paste". Once you get the mouse daemon running (see the previous question) hold down button 1 (left button) and move the mouse to select a region of text. Then, press button 2 (middle button) to paste it at the text cursor. Pressing button 3 (right button) will "extend" the selected region of text. If your mouse does not have a middle button, you may wish to emulate one or remap buttons using mouse daemon options. See the moused(8) manual page for details. | |
4.4.3. | My mouse has a fancy wheel and buttons. Can I use them in FreeBSD? |
The answer is, unfortunately, "It depends". These mice with additional features require specialized driver in most cases. Unless the mouse device driver or the user program has specific support for the mouse, it will act just like a standard two, or three button mouse. For the possible usage of wheels in the X Window environment, refer to that section. | |
4.4.4. | How do I use my delete key in |
For the Bourne Shell, add
the following lines to your bind ^? ed-delete-next-char # for consolebind ^[[3~ ed-delete-next-char # for xterm For the C Shell, add the
following lines to your bindkey ^? delete-char # for consolebindkey ^[[3~ delete-char # for xterm For more information, see this page. |
4.5.1. | Workarounds for no sound from my pcm(4) sound card? |
Some sound cards set their output volume to 0 at every boot. Run the following command every time the machine boots: # mixer pcm 100 vol 100 cd 100 | |
4.5.2. | Does FreeBSD support power management on my laptop? |
FreeBSD supports the ACPI features found in modern hardware. Further information can be found in acpi(4). |
5.1. | Why is FreeBSD finding the wrong amount of memory on i386™ hardware? |
The most likely reason is the difference between physical memory addresses and virtual addresses. The convention for most PC hardware is to use the memory area between 3.5 GB and 4 GB for a special purpose (usually for PCI). This address space is used to access PCI hardware. As a result real, physical memory can not be accessed by that address space. What happens to the memory that should appear in that location is dependent on your hardware. Unfortunately, some hardware does nothing and the ability to use that last 500 MB of RAM is entirely lost. Luckily, most hardware remaps the memory to a higher location so that it can still be used. However, this can cause some confusion if you watch the boot messages. On a 32-bit version of FreeBSD, the memory appears lost, since it will be remapped above 4 GB, which a 32-bit kernel is unable to access. In this case, the solution is to build a PAE enabled kernel. See the entry on memory limits and about different memory limits on different platforms for more information. On a 64-bit version of FreeBSD, or when running a PAE-enabled kernel, FreeBSD will correctly detect and remap the memory so it is usable. During boot, however, it may seem as if FreeBSD is detecting more memory than the system really has, due to the described remapping. This is normal and the available memory will be corrected as the boot process completes. | |
5.2. | Why do my programs occasionally die with Signal 11 errors? |
Signal 11 errors are caused when your process has attempted to access memory which the operating system has not granted it access to. If something like this is happening at seemingly random intervals then you need to start investigating things very carefully. These problems can usually be attributed to either:
In particular, a dead giveaway that this is not a FreeBSD bug is if you see the problem when you are compiling a program, but the activity that the compiler is carrying out changes each time. For example, suppose you are running
What you should do: In the first case you can use a debugger e.g., gdb(1) to find the point in the program which is attempting to access a bogus address and then fix it. In the second case you need to verify that it is not your hardware at fault. Common causes of this include:
You should also read the SIG11 FAQ (listed below) which has excellent explanations of all these problems, albeit from a Linux® viewpoint. It also discusses how memory testing software or hardware can still pass faulty memory. Finally, if none of this has helped it is possible that you have just found a bug in FreeBSD, and you should follow the instructions to send a problem report. There is an extensive FAQ on this at the SIG11 problem FAQ. | |
5.3. | My system crashes with either Fatal trap 12: page fault in kernel mode, or panic:, and spits out a bunch of information. What should I do? |
The FreeBSD developers are very interested in these errors, but need some more information than just the error you see. Copy your full crash message. Then consult the FAQ section on kernel panics, build a debugging kernel, and get a backtrace. This might sound difficult, but you do not need any programming skills; you just have to follow the instructions. | |
5.4. | Why do I get the error maxproc limit exceeded by uid %i, please see tuning(7) and login.conf(5)? |
The FreeBSD kernel will only allow a certain number of
processes to exist at one time. The number is based on the
To adjust your If your machine is lightly loaded, and you are simply
running a very large number of processes, you can adjust
this with the | |
5.5. | Why does sendmail give me an error reading mail loops back to myself? |
You can find a detailed answer for this question in the Handbook. | |
5.6. | Why do full screen applications on remote machines misbehave? |
The remote machine may be setting your terminal type to
something other than the There are a number of possible work-arounds for this problem:
| |
5.7. | Why does it take so long to connect to my computer via
The symptom: there is a long delay between the time the TCP connection is established and the time when the client software asks for a password (or, in telnet(1)'s case, when a login prompt appears). The problem: more likely than not, the delay is caused by the server software trying to resolve the client's IP address into a hostname. Many servers, including the Telnet and SSH servers that come with FreeBSD, do this to store the hostname in a log file for future reference by the administrator. The remedy: if the problem occurs whenever you connect from your computer (the client) to any server, the problem is with the client; likewise, if the problem only occurs when someone connects to your computer (the server) the problem is with the server. If the problem is with the client, the only remedy is to fix the DNS so the server can resolve it. If this is on a local network, consider it a server problem and keep reading; conversely, if this is on the global Internet, you will most likely need to contact your ISP and ask them to fix it for you. If the problem is with the server, and this is on a
local network, you need to configure the server to be able to
resolve address-to-hostname queries for your local address
range. See the hosts(5) and named(8) manual pages
for more information. If this is on the global Internet,
the problem may be that your server's resolver is not
functioning correctly. To check, try to look up another
host — say, Following a fresh install of FreeBSD, it is also possible
that domain and name server information is missing from
| |
5.8. | Why does file: table is full show up repeatedly in dmesg(8)? |
This error message indicates you have exhausted the number of available file descriptors on your system. Please see the kern.maxfiles section of the Tuning Kernel Limits section of the Handbook for a discussion and solution. | |
5.9. | Why does the clock on my computer keep incorrect time? |
Your computer has two or more clocks, and FreeBSD has chosen to use the wrong one. Run dmesg(8), and check for lines that contain
# dmesg | grep TimecounterTimecounter "i8254" frequency 1193182 Hz quality 0Timecounter "ACPI-fast" frequency 3579545 Hz quality 1000Timecounter "TSC" frequency 2998570050 Hz quality 800Timecounters tick every 1.000 msec You can confirm this by checking the
# sysctl kern.timecounter.hardwarekern.timecounter.hardware: ACPI-fast It may be a broken ACPI timer. The simplest solution is
to disable the ACPI timer in
debug.acpi.disabled="timer" Or the BIOS may modify the TSC clock—perhaps to change the speed of the processor when running from batteries, or going into a power saving mode, but FreeBSD is unaware of these adjustments, and appears to gain or lose time. In this example, the # sysctl kern.timecounter.hardware=i8254kern.timecounter.hardware: TSC -> i8254 Your computer should now start keeping more accurate time. To have this change automatically run at boot time, add
the following line to
kern.timecounter.hardware=i8254 | |
5.10. | What does the error swap_pager: indefinite wait buffer: mean? |
This means that a process is trying to page memory to
disk, and the page attempt has hung trying to access the
disk for more than 20 seconds. It might be caused by bad
blocks on the disk drive, disk wiring, cables, or any other
disk I/O-related hardware. If the drive itself is actually
bad, you will also see disk errors in
| |
5.11. | What is a lock order reversal? |
The FreeBSD kernel uses a number of resource locks to arbitrate contention for certain resources. When multiple kernel threads try to obtain multiple resource locks, there's always the potential for a deadlock, where two threads have each obtained one of the locks and blocks forever waiting for the other thread to release one of the other locks. This sort of locking problem can be avoided if all threads obtain the locks in the same order. A run-time lock diagnostic system called witness(4), enabled in FreeBSD-CURRENT and disabled by default for stable branches and releases, detects the potential for deadlocks due to locking errors, including errors caused by obtaining multiple resource locks with a different order from different parts of the kernel. The witness(4) framework tries to detect this problem as it happens, and reports it by printing a message to the system console about a lock order reversal (often referred to also as LOR). It is possible to get false positives, as witness(4) is conservative. A true positive report does not mean that a system is dead-locked; instead it should be understood as a warning of the form "if you were unlucky, a deadlock would have happened here". Note:Problematic LORs tend to get fixed quickly, so check http://lists.FreeBSD.org/mailman/listinfo/freebsd-current before posting to the mailing lists. | |
5.12. | What does Called ... with the following non-sleepable locks held mean? |
This means that a function that may sleep was called while a mutex (or other unsleepable) lock was held. The reason this is an error is because mutexes are not intended to be held for long periods of time; they are supposed to only be held to maintain short periods of synchronization. This programming contract allows device drivers to use mutexes to synchronize with the rest of the kernel during interrupts. Interrupts (under FreeBSD) may not sleep. Hence it is imperative that no subsystem in the kernel block for an extended period while holding a mutex. To catch such errors, assertions may be added to the kernel that interact with the witness(4) subsystem to emit a warning or fatal error (depending on the system configuration) when a potentially blocking call is made while holding a mutex. In summary, such warnings are non-fatal, however with unfortunate timing they could cause undesirable effects ranging from a minor blip in the system's responsiveness to a complete system lockup. For additional information about locking in FreeBSD see locking(9). | |
5.13. | Why does
This error does not mean that the touch(1) utility
is missing. The error is instead probably due to the dates
of the files being set sometime in the future. If your
CMOS-clock is set to local time you need to run the command
6.1. | So, where are all the user applications? |
Please take a look at the ports page for info on software packages ported to FreeBSD. The list currently tops 24,000 and is growing daily, so come back to check often or subscribe to the FreeBSD announcements mailing list for periodic updates on new entries. Most ports should work on the
8. We also support the concept of a "package", essentially no more than a compressed binary distribution with a little extra intelligence embedded in it for doing whatever custom installation work is required. A package can be installed and uninstalled again easily without having to know the gory details of which files it includes. Use
pkg(7) on the specific package files
you are interested in installing. Package files can usually
be identified by their | |
6.2. | How do I download the Ports tree? Should I be using SVN? |
Any of the methods listed here work:
Any other method should be considered a legacy method. If you do not already use them, do not start. | |
6.3. | Does FreeBSD support Java™? |
Yes. Please see http://www.FreeBSD.org/java/. | |
6.4. | Why can I not build this port on my
9. |
If you are running a FreeBSD version that lags significantly behind -CURRENT or -STABLE, you may need to update your Ports Collection; see the Keeping Up section of the Porter's Handbook for further information on how to do this. If you are up to date, then someone might have committed a change to the port which works for -CURRENT but which broke the port for -STABLE. Please submit a bug report on this with the send-pr(1) command, since the Ports Collection is supposed to work for both the -CURRENT and -STABLE branches. | |
6.5. | I just tried to build |
First, always make sure that you have a complete
up-to-date Ports Collection. Errors that affect building
There are rare cases where | |
6.6. | I updated the sources, now how do I update my installed ports? |
FreeBSD does not include a port upgrading tool, but it does have some tools to make the upgrade process somewhat easier. You can also install additional tools to simplify port handling, see the Upgrading Ports section in the FreeBSD Handbook. | |
6.7. | Do I need to recompile every port each time I perform a major version update? |
By all means! While a recent system will run with software compiled under an older release, you will end up with things randomly crashing and failing to work once you start installing other ports or updating a portion of what you already have. When the system is upgraded, various shared libraries, loadable modules, and other parts of the system will be replaced with newer versions. Applications linked against the older versions may fail to start or, in other cases, fail to function properly. For more information, see the section on upgrades in the FreeBSD Handbook. | |
6.8. | Do I need to recompile every port each time I perform a minor version update? |
In general, no. FreeBSD developers do their utmost to guarantee binary compatibility across all releases with the same major version number. Any exceptions will be documented in the Release Notes, and advice given there should be followed. | |
6.9. | Why is |
Many people need to write shell scripts which will be portable across many systems. That is why POSIX® specifies the shell and utility commands in great detail. Most scripts are written in Bourne shell (sh(1)), and because several important programming interfaces (make(1), system(3), popen(3), and analogues in higher-level scripting languages like Perl and Tcl) are specified to use the Bourne shell to interpret commands. Because the Bourne shell is so often and widely used, it is important for it to be quick to start, be deterministic in its behavior, and have a small memory footprint. The existing implementation is our best effort at
meeting as many of these requirements simultaneously as we
can. To keep | |
6.10. | How do I create audio CDs from my MIDI files? |
To create audio CDs from MIDI files, first install
audio/timidity++ from
ports then install manually the GUS patches set by Eric A.
Welsh, available at % timidity -Ow -s 44100 -o /tmp/juke/01.wav 01.mid The WAV files can then be converted to other formats or burned onto audio CDs, as described in the FreeBSD Handbook. | |
6.11. | Where can I get an Office Suite for FreeBSD? |
The open-source Apache OpenOffice and LibreOffice office suites work natively on FreeBSD. FreeBSD also includes a variety of text editors, spreadsheets, and drawing programs in the Ports Collection. | |
6.12. | How can I convert from pkgng to the old package tools? |
Short answer: it is not possible. Longer answer: if you have made any changes using
7.1. | I would like to customize my kernel. Is it difficult? |
Not at all! Check out the kernel config section of the Handbook. Note:The new | |
7.2. | Why is my kernel so big? |
However, if you are running low on disk space, there
are different options to reduce the size of If you do not want the symbol files to be installed,
make sure you have the following line present in
WITHOUT_KERNEL_SYMBOLS=yes For more information see src.conf(5). If you do not want to build a debug kernel, make sure that both of the following are true:
Either of the above settings will cause your kernel to be built in debug mode. As long as you make sure you follow the steps above, you can build your kernel normally. If you want only the modules you use to be built
and installed, make sure you have a line like below in
MODULES_OVERRIDE= accf_http ipfw Replace accf_httpd ipfw with
a list of modules you need. Only these modules will be
built. This does not only reduce the size of the kernel
directory but also decreases the amount of time needed to
build your kernel. For more information see
You can also remove unneeded devices from your kernel to further reduce the size. See Q: 7.1 for more information. To put any of these options into effect you will have to build and install your new kernel. Most kernels ( | |
7.3. | Why does every kernel I try to build fail to compile,
even |
There are a number of possible causes for this problem. They are, in no particular order:
| |
7.4. | How can I verify which scheduler is in use on a running system? |
The name of the scheduler currently being used is
directly available as the value of the
% sysctl kern.sched.namekern.sched.name: ULE | |
7.5. | What is |
8.1. | How can I add my new hard disk to my FreeBSD system? |
See the Adding Disks section in the FreeBSD Handbook. | |
8.2. | How do I move my system over to my huge new disk? |
The best way is to reinstall the OS on the new disk, then move the user data over. This is highly recommended if you have been tracking -STABLE for more than one release, or have updated a release instead of installing a new one. You can install booteasy on both disks with boot0cfg(8), and dual boot them until you are happy with the new configuration. Skip the next paragraph to find out how to move the data after doing this. Alternatively, partition and label the new disk with either sade(8) or gpart(8). If the disks are MBR-formatted, you can also install booteasy on both disks with boot0cfg(8), so that you can dual boot to the old or new system after the copying is done. Now you have the new disk set up, and are ready to move
the data. Unfortunately, you cannot just blindly copy the
data. Things like device files (in
You should never use anything but dump(8) and
restore(8) to move the root file system. The
tar(1) command may work — then again, it may not.
You should also use dump(8) and restore(8) if you
are moving a single partition to another empty partition.
The sequence of steps to use
For example, if you are going to move root to
# newfs /dev/ada1s1a# mount /dev/ada1s1a /mnt# cd /mnt# dump 0af - / | restore rf - Rearranging your partitions with # newfs /dev/ada1s1a# mount /dev/ada1s1a /mnt# cd /mnt# dump 0af - / | restore rf -# cd var# dump 0af - /var | restore rf - To split a directory from its parent, say putting
# newfs /dev/ada1s1a# newfs /dev/ada1s1d# mount /dev/ada1s1a /mnt# mkdir /mnt/var# mount /dev/ada1s1d /mnt/var# cd /mnt# dump 0af - / | restore rf - You might prefer cpio(1), pax(1), tar(1) to dump(8) for user data. At the time of this writing, these are known to lose file flag information, so use them with caution. | |
8.3. | Which partitions can safely use Soft Updates? I have
heard that Soft Updates on |
Short answer: you can usually use Soft Updates safely on all partitions. Long answer: Soft Updates has two characteristics that may be undesirable on certain partitions. First, a Soft Updates partition has a small chance of losing data during a system crash. (The partition will not be corrupted; the data will simply be lost.) Second, Soft Updates can cause temporary space shortages. When using Soft Updates, the kernel can take up to thirty seconds to write changes to the physical disk. When a large file is deleted the file still resides on disk until the kernel actually performs the deletion. This can cause a very simple race condition. Suppose you delete one large file and immediately create another large file. The first large file is not yet actually removed from the physical disk, so the disk might not have enough room for the second large file. You get an error that the partition does not have enough space, although you know perfectly well that you just released a large chunk of space! When you try again mere seconds later, the file creation works as you expect. This has left more than one user scratching his head and doubting his sanity, the FreeBSD file system, or both. If a system should crash after the kernel accepts a chunk of data for writing to disk, but before that data is actually written out, data could be lost. This risk is extremely small, but generally manageable. These issues affect all partitions using Soft Updates. So, what does this mean for the root partition? Vital information on the root partition changes very rarely. If the system crashed during the thirty-second window after such a change is made, it is possible that data could be lost. This risk is negligible for most applications, but you should be aware that it exists. If your system cannot tolerate this much risk, do not use Soft Updates on the root file system!
Finally, dump(8) does not work in live mode (-L) on a filesystem, with Journaled Soft Updates (SU+J). | |
8.4. | Can I mount other foreign file systems under FreeBSD? |
FreeBSD supports a variety of other file systems.
FreeBSD also supports network file systems such as NFS (see mount_nfs(8)), NetWare (see mount_nwfs(8)), and Microsoft-style SMB file systems (see mount_smbfs(8)). You can find ports based on FUSE (sysutils/fusefs-kmod) for many other file systems. | |
8.5. | How do I mount a secondary DOS partition? |
The secondary DOS partitions are found after
all the primary partitions. For
example, if you have an "E" partition as the
second DOS partition on the second SCSI drive, there will be
a device file for "slice 5" in
# mount -t msdosfs /dev/da1s5 /dos/e | |
8.6. | Is there a cryptographic file system for FreeBSD? |
Yes. You can use either gbde(8) or geli(8), see the Encrypting Disk Partitions section of the FreeBSD Handbook. | |
8.7. | How can I use the Windows NT® loader to boot FreeBSD? |
The general idea is that you copy the first sector of
your native root FreeBSD partition into a file in the
DOS/Windows NT® partition. Assuming you name that file
something like [boot loader]timeout=30default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS[operating systems]multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Windows NT"C:\BOOTSECT.BSD="FreeBSD"C:\="DOS" If FreeBSD is installed on the same disk as the Windows NT®
boot partition simply copy
Warning:Do not simply copy
When the FreeBSD boot manager runs it records the last OS
booted by setting the active flag on the partition table
entry for that OS and then writes the whole 512-bytes of
itself back to the MBR so if you just copy
| |
8.8. | How do I boot FreeBSD and Linux® from LILO? |
If you have FreeBSD and Linux® on the same disk, just follow LILO's installation instructions for booting a non-Linux® operating system. Very briefly, these are: Boot Linux®, and add the following lines to
other=/dev/hda2 table=/dev/hda label=FreeBSD (the above assumes that your FreeBSD slice is known to
Linux® as If FreeBSD resides on another disk, you need to add
other=/dev/dab4 table=/dev/dab loader=/boot/chain.b label=FreeBSD In some cases you may need to specify the BIOS drive number to the FreeBSD boot loader to successfully boot off the second disk. For example, if your FreeBSD SCSI disk is probed by BIOS as BIOS disk 1, at the FreeBSD boot loader prompt you need to specify: Boot: 1:da(0,a)/boot/kernel/kernel You can configure boot(8) to automatically do this for you at boot time. The Linux®+FreeBSD mini-HOWTO is a good reference for FreeBSD and Linux® interoperability issues. | |
8.9. | How do I boot FreeBSD and Linux® using GRUB? |
Booting FreeBSD using GRUB is very simple. Just add the
following to your configuration file
title FreeBSD 6.1 root (hd0,a) kernel /boot/loader Where | |
8.10. | How do I boot FreeBSD and Linux® using BootEasy? |
Install LILO at the start of your Linux® boot partition instead of in the Master Boot Record. You can then boot LILO from BootEasy. If you are running Windows® and Linux® this is recommended anyway, to make it simpler to get Linux® booting again if you should need to reinstall Windows® (which is a Jealous Operating System, and will bear no other Operating Systems in the Master Boot Record). | |
8.11. | How do I change the boot prompt from
You can not do that with the standard boot manager
without rewriting it. There are a number of other boot
managers in the | |
8.12. | I have a new removable drive, how do I use it? |
If the drive already has a file system on it, you can use a command like this: # mount -t msdosfs /dev/da0s1 /mnt If the drive will only be used with FreeBSD systems it is better idea to stick a BSD file system on it, like UFS or ZFS. You will get long filename support, at least a 2X improvement in performance, and a lot more stability. If the drive will be used by other operating systems a more portable choice, such as msdosfs, is better. # dd if=/dev/zero of=/dev/da0 count=2# gpart create -s GPT /dev/da0# gpart add -t freebsd-ufs /dev/da0 Finally, create a new file system: # newfs /dev/da0p1 and mount it: # mount /dev/da0s1 /mnt It is a good idea to add a line
to /dev/da0p1 /mnt ufs rw,noauto 0 0 | |
8.13. | Why do I get Incorrect super block when mounting a CD-ROM? |
You have to tell mount(8) the type of the device that you want to mount. This is described in the Handbook section on optical media, specifically the section Using Data CDs. | |
8.14. | Why do I get Device not configured when mounting a CD-ROM? |
This generally means that there is no CD-ROM in the CD-ROM drive, or the drive is not visible on the bus. Please see the Using Data CDs section of the Handbook for a detailed discussion of this issue. | |
8.15. | Why do all non-English characters in filenames show up as "?" on my CDs when mounted in FreeBSD? |
Your CD-ROM probably uses the "Joliet" extension for storing information about files and directories. This is discussed in the Handbook chapter on creating and using CD-ROMs, specifically the section on Using Data CD-ROMs. | |
8.16. | I burned a CD under FreeBSD and now I can not read it under any other operating system. Why? |
You most likely burned a raw file to your CD, rather than creating an ISO 9660 file system. Take a look at the Handbook chapter on creating CD-ROMs, particularly the section on burning raw data CDs. | |
8.17. | How can I create an image of a data CD? |
This is discussed in the Handbook section on duplicating data CDs. For more on working with CD-ROMs, see the Creating CDs Section in the Storage chapter in the Handbook. | |
8.18. | Why can I not |
If you try to mount an audio CD, you will get an error
like cd9660: /dev/acd0c: Invalid
argument. This is because
| |
8.19. | How do I |
By default, mount(8) will attempt to mount the last
data track (session) of a CD. If you would like to load an
earlier session, you must use the | |
8.20. | How do I let ordinary users mount CD-ROMs, DVDs, USB drives, and other removable media? |
As # sysctl vfs.usermount=1 To make this persist across reboots, add the line
Users can only mount devices they have read
permissions to. To allow users to mount a device
permissions must be set in
For example, to allow users to mount the first USB drive add: # Allow all users to mount a USB drive. own /dev/da0 root:operator perm /dev/da0 0666 All users can now mount devices they could read onto a directory that they own: % mkdir ~/my-mount-point% mount -t msdosfs /dev/da0 ~/my-mount-point Unmounting the device is simple: % umount ~/my-mount-point Enabling Note:The device name used in the previous examples must be changed according to your configuration. | |
8.21. | The |
You need to understand what When a program is using a file, and you delete the file,
the file is not really removed from the file system until
the program stops using it. The file is immediately deleted
from the directory listing, however. You can see this
easily enough with a program such as
This situation is common on web servers. Many people
set up a FreeBSD web server and forget to rotate the log files.
The access log fills up Note that Soft Updates can delay the freeing of disk space; you might need to wait up to 30 seconds for the change to be visible! | |
8.22. | How can I add more swap space? |
In the Configuration and Tuning section of the Handbook, you will find a section describing how to do this. | |
8.23. | Why does FreeBSD see my disk as smaller than the manufacturer says it is? |
Disk manufacturers calculate gigabytes as a billion bytes each, whereas FreeBSD calculates them as 1,073,741,824 bytes each. This explains why, for example, FreeBSD's boot messages will report a disk that supposedly has 80 GB as holding 76,319 MB. Also note that FreeBSD will (by default) reserve 8% of the disk space. | |
8.24. | How is it possible for a partition to be more than 100% full? |
A portion of each UFS partition (8%, by default) is
reserved for use by the operating system and the
For more details, look up | |
8.25. | Why does FreeBSD pause for a long time at boot when the system has large amounts of ram? |
FreeBSD does a short memory test early in the boot
process. This test usually only takes several seconds,
however if the system has many 10s or 100s of gigabytes
of memory it can take up to a few minutes. This test
can be disabled by setting
For more details, see loader.conf(5). |
8.1.1. | What is the minimum amount of RAM one should have to run ZFS? |
A minimum of 4GB of RAM is required for comfortable usage, but individual workloads can vary widely. | |
8.1.2. | What is the ZIL and when does it get used? |
The ZIL ((ZFS intent log) is a write log used to implement posix write commitment semantics across crashes. Normally writes are bundled up into transaction groups and written to disk when filled ("Transaction Group Commit"). However syscalls like fsync(2) require a commitment that the data is written to stable storage before returning. The ZIL is needed for writes that have been acknowledged as written but which are not yet on disk as part of a transaction. The transaction groups are timestamped. In the event of a crash the last valid timestamp is found and missing data is merged in from the ZIL. | |
8.1.3. | Do I need a SSD for ZIL? |
By default, ZFS stores the ZIL in the pool with all the data. If your application has a heavy write load, storing the ZIL in a separate device that has very fast synchronous, sequential write performance can improve overall system. For other workloads, a SSD is unlikely to make much of an improvement. | |
8.1.4. | What is the L2ARC? |
The L2ARC is a read cache stored on a fast device such as an SSD. This cache is not persistent across reboots. Note that RAM is used as the first layer of cache and the L2ARC is only needed if there is insufficient RAM. L2ARC needs space in the ARC to index it. So, perversely, a working set that fits perfectly in the ARC will not fit perfectly any more if a L2ARC is used because part of the ARC is holding the L2ARC index, pushing part of the working set into the L2ARC which is slower than RAM. | |
8.1.5. | Is enabling deduplication advisable? |
Generally speaking, no. Deduplication takes up a significant amount of RAM and may slow down read and write disk access times. Unless one is storing data that is very heavily duplicated (such as virtual machine images, or user backups) it is possible that deduplication will do more harm than good. Another consideration is the inability to revert deduplication status. If data is written when deduplication is enabled, disabling dedup will not cause those blocks which were deduplicated to be replicated until they are next modified. Deduplication can also lead to some unexpected situations. In particular deleting files may become much slower. | |
8.1.6. | I can not delete or create files on my ZFS pool. How can I fix this? |
This could happen because the pool is 100% full. ZFS requires space on the disk to write transaction metadata. To restore the pool to a usable state, truncate a file you want to delete. % truncate -s 0 unimportant-file File truncation works because a new transaction is not started, new spare blocks are created instead. Note:On systems with additional ZFS dataset tuning, such as deduplication, the space may not be immediately available | |
8.1.7. | Does ZFS support TRIM for Solid State Drives? |
ZFS TRIM support was added to FreeBSD 10-CURRENT with revision r240868. ZFS TRIM support is not yet available on the -STABLE branches. ZFS TRIM is enabled by default, and can be turned
off by adding this line to
vfs.zfs.trim_disable=1 Note:ZFS TRIM may not work with all configurations, such as a ZFS filesystem on a GELI-backed device. |
9.1. | Where are the system start-up configuration files? | ||||||||
The primary configuration file is
For example, if you wish to start named(8), the included DNS server, all you need to do is: # echo 'named_enable="YES"' >> /etc/rc.conf To start up local services, place shell scripts in the
| |||||||||
9.2. | How do I add a user easily? | ||||||||
Use the adduser(8) command, or the pw(8) command for more complicated situations. To remove the user, use the rmuser(8) command or, if necessary, pw(8). | |||||||||
9.3. | Why do I keep getting messages like root: not
found after editing
| ||||||||
This is normally caused by editing the system crontab
( # crontab /etc/crontab This is not the correct way to do things. The system crontab has a different format to the per-user crontabs which crontab(1) updates (the crontab(5) manual page explains the differences in more detail). If this is what you did, the extra crontab is simply a
copy of # crontab -r Next time, when you edit
If you want something to be run once per day, week, or
month, it is probably better to add shell scripts
The actual reason for the error is that the system
crontab has an extra field, specifying which user to run the
command as. In the default system crontab provided with
FreeBSD, this is | |||||||||
9.4. | Why do I get the error, you are not in the
correct group to su root when I try to
| ||||||||
This is a security feature. To
To allow someone to # pw groupmod wheel -m lisa The above example will add user
| |||||||||
9.5. | I made a mistake in | ||||||||
Restart the system using If you intend to use a full screen editor such as
vi(1) or emacs(1), you may also need to run
Once you have performed these steps, you can edit
| |||||||||
9.6. | Why am I having trouble setting up my printer? | ||||||||
See the Handbook entry on printing. It should cover most of your problem. Some printers require a host-based driver to do any kind of printing. These so-called "WinPrinters" are not natively supported by FreeBSD. If your printer does not work in DOS or Windows®, it is probably a WinPrinter. Your only hope of getting one of these to work is to check if the print/pnm2ppa port supports it. | |||||||||
9.7. | How can I correct the keyboard mappings for my system? | ||||||||
Please see the Handbook section on using localization, specifically the section on console setup. | |||||||||
9.8. | Why can I not get user quotas to work properly? | ||||||||
| |||||||||
9.9. | Does FreeBSD support System V IPC primitives? | ||||||||
Yes, FreeBSD supports System V-style IPC, including shared
memory, messages and semaphores, in the
options SYSVSHM # enable shared memoryoptions SYSVSEM # enable for semaphoresoptions SYSVMSG # enable for messaging Recompile and install your kernel. | |||||||||
9.10. | What other mail-server software can I use instead of sendmail? | ||||||||
The sendmail server is the default mail-server software for FreeBSD, but you can easily replace it with one of the other MTA (for instance, an MTA installed from the ports). There are various alternative MTAs in the ports tree already, with mail/exim, mail/postfix, mail/qmail, and mail/zmailer being some of the most popular choices. Diversity is nice, and the fact that you have many different mail-servers to chose from is considered a good thing; therefore try to avoid asking questions like "Is sendmail better than qmail?" in the mailing lists. If you do feel like asking, first check the mailing list archives. The advantages and disadvantages of each and every one of the available MTAs have already been discussed a few times. | |||||||||
9.11. | I have forgotten the | ||||||||
Do not panic! Restart the system, type
Note:If you are still prompted to give the
Note:If you cannot mount your root partition from Single User mode, it is possible that the partitions are encrypted and it is impossible to mount them without the access keys. Your chances depend on the chosen implementation. For more information see the section about encrypted disks in the FreeBSD Handbook. | |||||||||
9.12. | How do I keep Control+Alt+Delete from rebooting the system? | ||||||||
If you are using syscons(4) (the default console driver) build and install a new kernel with the line in the configuration file: options SC_DISABLE_REBOOT This can also be done by setting the following sysctl(8) which does not require a reboot or kernel recompile: # sysctl hw.syscons.kbd_reboot=0 Note:The above two methods are exclusive: The sysctl(8)
does not exist if you compile your kernel with the
| |||||||||
9.13. | How do I reformat DOS text files to UNIX® ones? | ||||||||
Use this perl(1) command: % perl -i.bak -npe 's/\r\n/\n/g' file(s) where Alternatively you can use the tr(1) command: % tr -d '\r' < dos-text-file > unix-file
Yet another way to reformat DOS text files is to use the converters/dosunix port from the Ports Collection. Consult its documentation about the details. | |||||||||
9.14. | How do I kill processes by name? | ||||||||
Use pkill(1). | |||||||||
9.15. | How do I re-read | ||||||||
Go into single user mode and then back to multi user mode. On the console do: # shutdown now(Note: without -r or -h)# return# exit | |||||||||
9.16. | I tried to update my system to the latest
-STABLE, but got
Short answer: it is just a name. RC stands for "Release Candidate". It signifies that a release is imminent. In FreeBSD, -PRERELEASE is typically synonymous with the code freeze before a release. (For some releases, the -BETA label was used in the same way as -PRERELEASE.) Long answer: FreeBSD derives its releases from one of two places. Major, dot-zero, releases, such as 9.0-RELEASE are branched from the head of the development stream, commonly referred to as -CURRENT. Minor releases, such as 6.3-RELEASE or 5.2-RELEASE, have been snapshots of the active -STABLE branch. Starting with 4.3-RELEASE, each release also now has its own branch which can be tracked by people requiring an extremely conservative rate of development (typically only security advisories). When a release is about to be made, the branch from which it will be derived from has to undergo a certain process. Part of this process is a code freeze. When a code freeze is initiated, the name of the branch is changed to reflect that it is about to become a release. For example, if the branch used to be called 6.2-STABLE, its name will be changed to 6.3-PRERELEASE to signify the code freeze and signify that extra pre-release testing should be happening. Bug fixes can still be committed to be part of the release. When the source code is in shape for the release the name will be changed to 6.3-RC to signify that a release is about to be made from it. Once in the RC stage, only the most critical bugs found can be fixed. Once the release (6.3-RELEASE in this example) and release branch have been made, the branch will be renamed to 6.3-STABLE. For more information on version numbers and the various Subversion branches, refer to the Release Engineering article. | |||||||||
9.17. | I tried to install a new kernel, and the chflags(1) failed. How do I get around this? | ||||||||
Short answer: You are probably at security level greater than 0. Reboot directly to Single User mode to install the kernel. Long answer: FreeBSD disallows changing system flags at security levels greater than 0. You can check your security level with the command: # sysctl kern.securelevel You cannot lower the security level; you have to boot to
Single Mode to install the kernel, or change the security
level in | |||||||||
9.18. | I cannot change the time on my system by more than one second! How do I get around this? | ||||||||
Short answer: You are probably at security level greater than 1. Reboot directly to Single User mode to change the date. Long answer: FreeBSD disallows changing the time by more that one second at security levels greater than 1. You can check your security level with the command: # sysctl kern.securelevel You cannot lower the security level; you have to boot to
Single User mode to change the date, or change the security
level in | |||||||||
9.19. | Why is | ||||||||
No, there is no memory leak, and it is not using
256 MB of memory. For convenience,
rpc.statd(8) maps its status file (resident on
| |||||||||
9.20. | Why can I not unset the | ||||||||
You are running at an elevated (i.e., greater than 0) securelevel. Lower the securelevel and try again. For more information, see the FAQ entry on securelevel and the init(8) manual page. | |||||||||
9.21. | Why does SSH authentication
through | ||||||||
The reason why
| |||||||||
9.22. | What is | ||||||||
| |||||||||
9.23. | What do the various memory states displayed by
| ||||||||
Pages are most often written to disk (sort of a VM sync) when they are in the inactive state, but active pages can also be synced. This depends upon the CPU tracking of the modified bit being available, and in certain situations there can be an advantage for a block of VM pages to be synced, whether they are active or inactive. In most common cases, it is best to think of the inactive queue to be a queue of relatively unused pages that might or might not be in the process of being written to disk. Cached pages are already synced, not mapped, but available for immediate process use with their old association or with a new association. Free pages are available at interrupt level, but cached or free pages can be used at process state for reuse. Cache pages are not adequately locked to be available at interrupt level. There are some other flags (e.g., busy flag or busy count) that might modify some of the described rules. | |||||||||
9.24. | How much free memory is available? | ||||||||
There are a couple of kinds of "free memory". One kind is the amount of memory immediately available without paging anything else out. That is approximately the size of cache queue + size of free queue (with a derating factor, depending upon system tuning). Another kind of "free memory" is the total amount of VM space. That can be complex, but is dependent upon the amount of swap space and memory. Other kinds of "free memory" descriptions are also possible, but it is relatively useless to define these, but rather it is important to make sure that the paging rate is kept low, and to avoid running out of swap space. | |||||||||
9.25. | What is | ||||||||
Although it is not recommended to delete this directory, to
do so you will need to unset the | |||||||||
9.26. | I just changed
| ||||||||
To see what newsyslog(8) will do use the following: % newsyslog -nrvv | |||||||||
9.27. | My time is wrong, how can I change the timezone? | ||||||||
Use tzsetup(8). |
10.1. | What is the X Window System? |
The X Window System (commonly Many implementations are available for different
architectures and operating systems. An implementation of
the server-side code is properly known as an | |
10.2. | I want to run Xorg, how do I go about it? |
To install Xorg do one of the following: Use the x11/xorg meta-port, which builds and installs every Xorg component. Use x11/xorg-minimal, which builds and installs only the necessary Xorg components. Install Xorg from FreeBSD packages: # pkg_add -r xorg or on systems using pkg: # pkg install xorg After the installation of Xorg, follow the instructions from the X11 Configuration section of the FreeBSD Handbook. | |
10.3. | I tried to run X, but I get a
No devices detected. error when I
Your system is probably running at a raised
There are two solutions to the problem:
Set your
See Q: 10.10 for more information about running xdm(1) at boot time. | |
10.4. | Why does my mouse not work with X? |
If you are using syscons(4) (the default console
driver), you can configure FreeBSD to support a mouse pointer on
each virtual screen. To avoid conflicting with X,
syscons(4) supports a virtual device called
Then edit Section "InputDevice" Option "Protocol" "SysMouse" Option "Device" "/dev/sysmouse"..... Starting with Xorg version 7.4, the
Option "AutoAddDevices" "false" Some people prefer to use
link sysmouse mouse This link can be created by restarting devfs(5)
with the following command (as
# service devfs restart | |
10.5. | My mouse has a fancy wheel. Can I use it in X? |
Yes. You need to tell X that you have a 5 button mouse. To
do this, simply add the lines Example 10.1. "InputDevice" Section for Wheeled Mouse
in Xorg Configuration File Section "InputDevice" Identifier "Mouse1" Driver "mouse" Option "Protocol" "auto" Option "Device" "/dev/sysmouse" Option "Buttons" "5" Option "ZAxisMapping" "4 5"EndSection Example 10.2. ".emacs" Example for Naive Page
Scrolling with Wheeled Mouse (optional) ;; wheel mouse(global-set-key [mouse-4] 'scroll-down)(global-set-key [mouse-5] 'scroll-up) | |
10.6. | My laptop has a Synaptics touchpad. Can I use it in X? |
Yes, you will have to configure a few things to make it work. If you plan to use the Xorg synaptics driver you
must remove moused_enable from
To enable synaptics in the psm(4) driver you need
to add the following into
hw.psm.synaptics_support="1" You also need the following into
Section "InputDevice"Identifier "Touchpad0"Driver "synaptics"Option "Protocol" "psm"Option "Device" "/dev/psm0"EndSection And be sure to add the following into the "ServerLayout" section: InputDevice "Touchpad0" "SendCoreEvents" | |
10.7. | How do I use remote X displays? |
For security reasons, the default setting is to not allow a machine to remotely open a window. To enable this feature, simply start
X with the optional
% startx -listen_tcp | |
10.8. | What is a virtual console and how do I make more? |
Virtual consoles, put simply, enable you to have several simultaneous sessions on the same machine without doing anything complicated like setting up a network or running X. When the system starts, it will display a login prompt on the monitor after displaying all the boot messages. You can then type in your login name and password and start working (or playing!) on the first virtual console. At some point, you will probably wish to start another session, perhaps to look at documentation for a program you are running or to read your mail while waiting for an FTP transfer to finish. Just do Alt+F2 (hold down Alt and press F2), and you will find a login prompt waiting for you on the second "virtual console"! When you want to go back to the original session, do Alt+F1. The default FreeBSD installation has eight virtual consoles enabled. Alt+F1, Alt+F2, Alt+F3, and so on will switch between these virtual consoles. To enable more of them, edit
# Edit the existing entry for ttyv8 in /etc/ttys and change# "off" to "on".ttyv8 "/usr/libexec/getty Pc" xterm on securettyv9 "/usr/libexec/getty Pc" xterm on securettyva "/usr/libexec/getty Pc" xterm on securettyvb "/usr/libexec/getty Pc" xterm on secure Use as many or as few as you want. The more virtual
terminals you have, the more resources that are used; this
can be important if you have 8 MB RAM or less. You may
also want to change the Note:Versions of FreeBSD prior to 9.0 used the "
cons25" terminal type, and not "
xterm". Existing entries in
Important:If you want to run an X server you must leave at least one virtual terminal unused (or turned off) for it to use. That is to say that if you want to have a login prompt pop up for all twelve of your Alt-function keys, you are out of luck — you can only do this for eleven of them if you also want to run an X server on the same machine. The easiest way to disable a console is by turning it off. For example, if you had the full 12 terminal allocation mentioned above and you wanted to run X, you would change settings for virtual terminal 12 from: ttyvb "/usr/libexec/getty Pc" xterm on secure to: ttyvb "/usr/libexec/getty Pc" xterm off secure If your keyboard has only ten function keys, you would end up with: ttyv9 "/usr/libexec/getty Pc" xterm off securettyva "/usr/libexec/getty Pc" xterm off securettyvb "/usr/libexec/getty Pc" xterm off secure (You could also just delete these lines.) Next, the easiest (and cleanest) way to activate the
virtual consoles is to reboot. However, if you really do
not want to reboot, you can just shut down the X Window
system and execute (as # kill -HUP 1 It is imperative that you completely shut down X Window
if it is running, before running this command. If you do not,
your system will probably appear to hang or lock up after
executing | |
10.9. | How do I access the virtual consoles from X? |
Use Ctrl+Alt+F Once you are back to a text console, you can then use
Alt+F To return to the X session, you must switch to the
virtual console running X. If you invoked X from the
command line, (e.g., using | |
10.10. | How do I start XDM on boot? |
There are two schools of thought on how to start
xdm(1). One school starts The ttys(5) method has the advantage of documenting
which vty X will start on and passing the responsibility of
restarting the X server on logout to init(8). The
rc(8) method makes it easy to If loaded from rc(8), If you are to start :0 local /usr/local/bin/X vt4 The above example will direct the X server to run in
| |
10.11. | Why do I get Couldn't open
console when I run
If you start X with
This is because of the way console permissions are set by default. On a multi-user system, one does not necessarily want just any user to be able to write on the system console. For users who are logging directly onto a machine with a VTY, the fbtab(5) file exists to solve such problems. In a nutshell, make sure an uncommented line of the form
is in /dev/ttyv0 0600 /dev/console It will ensure that whomever logs in on
| |
10.12. | Why does my PS/2 mouse misbehave under X? |
Your mouse and the mouse driver may have somewhat become out of synchronization. In rare cases the driver may erroneously report synchronization problem and you may see the kernel message: psmintr: out of sync (xxxx != yyyy) and notice that your mouse does not work properly. If this happens, disable the synchronization check code
by setting the driver flags for the PS/2 mouse driver to
| |
10.13. | How do I reverse the mouse buttons? |
Run the command
You add the above command to
| |
10.14. | How do I install a splash screen and where do I find them? |
The detailed answer for this question can be found in the Boot Time Splash Screens section of the FreeBSD Handbook. | |
10.15. | Can I use the Windows keys on my keyboard in X? |
Yes. All you need to do is use xmodmap(1) to define what function you wish them to perform. Assuming all "Windows" keyboards are standard then the keycodes for these three keys are the following:
To have the left Windows key print a comma, try this. # xmodmap -e "keycode 115 = comma" To have the Windows key-mappings
enabled automatically every time you start X either put the
xmodmap $HOME/.xmodmaprc For example, you could map the 3 keys to be F13, F14, and F15, respectively. This would make it easy to map them to useful functions within applications or your window manager, as demonstrated further down. To do this put the following in
keycode 115 = F13keycode 116 = F14keycode 117 = F15 If you use the x11-wm/fvwm2 port, for example, you could map the keys so that F13 iconifies (or de-iconifies) the window the cursor is in, F14 brings the window the cursor is in to the front or, if it is already at the front, pushes it to the back, and F15 pops up the main Workplace (application) menu even if the cursor is not on the desktop, which is useful if you do not have any part of the desktop visible (and the logo on the key matches its functionality). The following entries in Key F13 FTIWS A IconifyKey F14 FTIWS A RaiseLowerKey F15 A A Menu Workplace Nop | |
10.16. | How can I get 3D hardware acceleration for OpenGL®? |
The availability of 3D acceleration depends on the version of Xorg that you are using and the type of video chip you have. If you have an nVidia chip, you can use the binary drivers provided for FreeBSD by installing one of the following ports:
nVidia provides detailed information on which
card is supported by which driver
on their web site: For Matrox G200/G400, check the x11-servers/mga_hal port. For ATI Rage 128 and Radeon see ati(4), r128(4) and radeon(4). |
11.1. | Where can I get information on "diskless booting"? |
"Diskless booting" means that the FreeBSD box is booted over a network, and reads the necessary files from a server instead of its hard disk. For full details, please read the Handbook entry on diskless booting. | |
11.2. | Can a FreeBSD box be used as a dedicated network router? |
Yes. Please see the Handbook entry on advanced networking, specifically the section on routing and gateways. | |
11.3. | Can I connect my Windows® box to the Internet via FreeBSD? |
Typically, people who ask this question have two PCs at home, one with FreeBSD and one with some version of Windows® the idea is to use the FreeBSD box to connect to the Internet and then be able to access the Internet from the Windows® box through the FreeBSD box. This is really just a special case of the previous question and works perfectly well. Dialup users must use If you are using kernel-mode PPP or have an Ethernet connection to the Internet, you need to use natd(8). Please look at the natd section of the Handbook for a tutorial. | |
11.4. | Does FreeBSD support PPP? |
Yes. ppp(8) provides support for both incoming and outgoing connections. For more information on how to use this, please see the Handbook chapter on PPP. | |
11.5. | Does FreeBSD support NAT or Masquerading? |
Yes. If you want to use NAT over a user PPP connection, please see the Handbook entry on user PPP. If you want to use NAT over some other sort of network connection, please look at the natd section of the Handbook. | |
11.6. | How can I set up Ethernet aliases? |
If the alias is on the same subnet as an address already
configured on the interface, then add # ifconfig ed0 alias 192.0.2.2 netmask 0xffffffff Otherwise, just specify the network address and netmask as usual: # ifconfig ed0 alias 172.16.141.5 netmask 0xffffff00 You can read more about this in the FreeBSD Handbook. | |
11.7. | Why can I not NFS-mount from a Linux® box? |
Some versions of the Linux® NFS code only accept mount requests from a privileged port; try to issue the following command: # mount -o -P linuxbox:/blah /mnt | |
11.8. | Why does |
The most frequent problem is not understanding the
correct format of | |
11.9. | How do I enable IP multicast support? |
FreeBSD supports multicast host operations by default. If
you want your box to run as a multicast router, you need to
recompile your kernel with the Note:In recent FreeBSD releases, the mrouted(8) multicast routing daemon, the map-mbone(8) and mrinfo(8) utilities have been removed from the base system. These programs are now available in the FreeBSD Ports Collection as net/mrouted. | |
11.10. | Why do I have to use the FQDN for hosts on my site? |
See the answer in the FreeBSD Handbook. | |
11.11. | Why do I get an error, Permission denied, for all networking operations? |
If you have compiled your kernel with the
If you had unintentionally misconfigured your system for
firewalling, you can restore network operability by typing
the following while logged in as
# ipfw add 65534 allow all from any to any You can also set For further information on configuring a FreeBSD firewall, see the Handbook chapter. | |
11.12. | Why is my |
Possibly because you want to do network address translation (NAT) and not just forward packets. A "fwd" rule does exactly what it says; it forwards packets. It does not actually change the data inside the packet. Say we have a rule like: 01000 fwd 10.0.0.1 from any to foo 21 When a packet with a destination address of
See the FAQ about redirecting services, the natd(8) manual, or one of the several port redirecting utilities in the Ports Collection for a correct way to do this. | |
11.13. | How can I redirect service requests from one machine to another? |
You can redirect FTP (and other service) request with
the sysutils/socket
port. Simply replace the service's command line to call
ftp stream tcp nowait nobody /usr/local/bin/socket socket ftp.example.com ftp where | |
11.14. | Where can I get a bandwidth management tool? |
There are three bandwidth management tools available for FreeBSD. dummynet(4) is integrated into FreeBSD as part of ipfw(4). ALTQ has been integrated into FreeBSD as part of pf(4). Bandwidth Manager from Emerging Technologies is a commercial product. | |
11.15. | Why do I get /dev/bpf0: device not configured? |
You are running a program that requires the Berkeley Packet Filter (bpf(4)), but it is not in your kernel. Add this to your kernel config file and build a new kernel: device bpf # Berkeley Packet Filter | |
11.16. | How do I mount a disk from a Windows® machine that is on my network, like smbmount in Linux®? |
Use the SMBFS toolset. It includes a set of kernel modifications and a set of userland programs. The programs and information are available as mount_smbfs(8) in the base system. | |
11.17. | What are these messages about: Limiting icmp/open port/closed port response in my log files? |
This is the kernel telling you that some activity is provoking it to send more ICMP or TCP reset (RST) responses than it thinks it should. ICMP responses are often generated as a result of attempted connections to unused UDP ports. TCP resets are generated as a result of attempted connections to unopened TCP ports. Among others, these are the kinds of activities which may cause these messages:
The first number in the message tells you how many
packets the kernel would have sent if the limit was not in
place, and the second number tells you the limit. You can
control the limit using the
# sysctl net.inet.icmp.icmplim=300 If you do not want to see messages about this in your
log files, but you still want the kernel to do response
limiting, you can use the
# sysctl net.inet.icmp.icmplim_output=0 Finally, if you want to disable response limiting, you
can set the | |
11.18. | What are these arp: unknown hardware address format error messages? |
This means that some device on your local Ethernet is using a MAC address in a format that FreeBSD does not recognize. This is probably caused by someone experimenting with an Ethernet card somewhere else on the network. You will see this most commonly on cable modem networks. It is harmless, and should not affect the performance of your FreeBSD machine. | |
11.19. | Why do I keep seeing messages like: 192.168.0.10 is on fxp1 but got reply from 00:15:17:67:cf:82 on rl0, and how do I disable it? |
Because a packet is coming from outside the network
unexpectedly. To disable them, set
12.1. | What is a sandbox? |
"Sandbox" is a security term. It can mean two things:
UNIX® implements two core sandboxes. One is at the process level, and one is at the userid level. Every UNIX® process is completely firewalled off from every other UNIX® process. One process cannot modify the address space of another. A UNIX® process is owned by a particular userid. If
the user ID is not the | |
12.2. | What is securelevel? |
To check the status of the securelevel on a running system, simply execute the following command: # sysctl -n kern.securelevel The output contains the current value of the securelevel. If it is positive (i.e., greater than 0), at least some of the securelevel's protections are enabled. The securelevel of a running system can not be
lowered as this would defeat its purpose. If you need
to do a task that requires that the securelevel be
non-positive (e.g., an For more information on securelevel and the specific things all the levels do, please consult the init(8) manual page. Warning:Securelevel is not a silver bullet; it has many known deficiencies. More often than not, it provides a false sense of security. One of its biggest problems is that in order for it to be at all effective, all files used in the boot process up until the securelevel is set must be protected. If an attacker can get the system to execute their code prior to the securelevel being set (which happens quite late in the boot process since some things the system must do at start-up cannot be done at an elevated securelevel), its protections are invalidated. While this task of protecting all files used in the boot process is not technically impossible, if it is achieved, system maintenance will become a nightmare since one would have to take the system down, at least to single-user mode, to modify a configuration file. This point and others are often discussed on the mailing lists, particularly the FreeBSD security mailing list. Please search the archives here for an extensive discussion. A more fine-grained mechanism is preferred. | |
BIND uses a random high-numbered port for outgoing
queries. Recent versions of it choose a new, random UDP
port for each query. This may cause problems for some
network configurations, especially if a firewall blocks
incoming UDP packets on particular ports. If you want to
get past that firewall, you can try the
Warning:If a port number (like 53) is specified via the
Congratulations, by the way. It is good practice to read your sockstat(1) output and notice odd things! | |
12.4. | The sendmail daemon is listening on port 587 as well as the standard port 25! What is going on? |
Recent versions of sendmail support a mail submission feature that runs over port 587. This is not yet widely supported, but is growing in popularity. | |
12.5. | What is this UID 0 |
Do not worry. Some people use |
13.1. | I cannot make ppp(8) work. What am I doing wrong? |
You should first read the ppp(8) manual page and the PPP section of the handbook. Enable logging with the following command: set log Phase Chat Connect Carrier lcp ipcp ccp command This command may be typed at the ppp(8) command
prompt or it may be entered in the
!ppp*.* /var/log/ppp.log You can now find out a lot about what is going on from the log file. Do not worry if it does not all make sense. If you need to get help from someone, it may make sense to them. | |
13.2. | Why does ppp(8) hang when I run it? |
This is usually because your hostname will not resolve.
The best way to fix this is to make sure that
127.0.0.1 foo.example.com foo localhost Otherwise, simply add another entry for your host. Consult the relevant manual pages for more details. You should be able to successfully
| |
13.3. | Why will ppp(8) not dial in
First, check that you have got a default route. By
running Destination Gateway Flags Refs Use Netif Expiredefault 10.0.0.2 UGSc 0 0 tun010.0.0.2 10.0.0.1 UH 0 0 tun0 This is assuming that you have used the addresses from
the handbook, the manual page, or from
Another reason for the default route line being missing
is that you have mistakenly set up a default router in your
delete ALL If this is the case, go back to the Final System Configuration section of the handbook. | |
13.4. | What does No route to host mean? |
This error is usually due that the following section is
missing in your MYADDR: delete ALL add 0 0 HISADDR This is only necessary if you have a dynamic IP address
or do not know the address of your gateway. If you are
using interactive mode, you can type the following after
entering delete ALLadd 0 0 HISADDR Refer to the PPP and Dynamic IP addresses section of the handbook for further details. | |
13.5. | Why does my connection drop after about 3 minutes? |
The default PPP timeout is 3 minutes. This can be adjusted with the following line: set timeout NNN where | |
13.6. | Why does my connection drop under heavy load? |
If you have Link Quality Reporting (LQR) configured, it is possible that too many LQR packets are lost between your machine and the peer. ppp(8) deduces that the line must therefore be bad, and disconnects. LQR is disabled by default and can be enabled with the following line: enable lqr | |
13.7. | Why does my connection drop after a random amount of time? |
Sometimes, on a noisy phone line or even on a line with call waiting enabled, your modem may hang up because it thinks (incorrectly) that it lost carrier. There is a setting on most modems for determining how tolerant it should be to temporary losses of carrier. Refer to the modem manual for details. | |
13.8. | Why does my connection hang after a random amount of time? |
Many people experience hung connections with no apparent explanation. The first thing to establish is which side of the link is hung. If you are using an external modem, you can simply try
using ping(8) to see if the TD light
is flashing when you transmit data. If it flashes (and the
RD light does not), the problem is with
the remote end. If TD does not flash,
the problem is local. With an internal modem, you will need
to use the Having established whether the problem is local or remote, you now have two possibilities: | |
13.9. | The remote end is not responding. What can I do? |
There is very little you can do about this. Most ISPs
will refuse to help if you are not running a Microsoft® OS.
You can First, try disabling all local compression by adding the following to your configuration: disable pred1 deflate deflate24 protocomp acfcomp shortseq vjdeny pred1 deflate deflate24 protocomp acfcomp shortseq vj Then reconnect to ensure that this makes no difference. If things improve or if the problem is solved completely, determine which setting makes the difference through trial and error. This will provide good ammunition when you contact your ISP (although it may make it apparent that you are not running a Microsoft® product). Before contacting your ISP, enable async logging locally and wait until the connection hangs again. This may use up quite a bit of disk space. The last data read from the port may be of interest. It is usually ASCII data, and may even describe the problem (Memory fault, Core dumped). If your ISP is helpful, they should be able to enable logging on their end, then when the next link drop occurs, they may be able to tell you why their side is having a problem. | |
13.10. | ppp(8) has hung. What can I do? |
Your best bet here is to rebuild ppp(8) with debugging information, and then use gdb(1) to grab a stack trace from the ppp process that is stuck. To rebuild the ppp utility with debugging information, you can type: # cd /usr/src/usr.sbin/ppp# env DEBUG_FLAGS='-g' make clean# env DEBUG_FLAGS='-g' make install Then you should restart ppp and wait until it hangs again. When the debug build of ppp hangs, start gdb on the stuck process by typing: # gdb ppp `pgrep ppp` At the gdb prompt, you can
use the | |
13.11. | I keep seeing errors about magic being the same. What does it mean? |
Occasionally, just after connecting, you may see messages in the log that say Magic is same. Sometimes, these messages are harmless, and sometimes one side or the other exits. Most PPP implementations cannot survive this problem, and even if the link seems to come up, you will see repeated configure requests and configure acknowledgments in the log file until ppp(8) eventually gives up and closes the connection. This normally happens on server machines with slow disks that are spawning a getty(8) on the port, and executing ppp(8) from a login script or program after login. There were reports of it happening consistently when using slirp. The reason is that in the time taken between getty(8) exiting and ppp(8) starting, the client-side ppp(8) starts sending Line Control Protocol (LCP) packets. Because ECHO is still switched on for the port on the server, the client ppp(8) sees these packets "reflect" back. One part of the LCP negotiation is to establish a magic number for each side of the link so that "reflections" can be detected. The protocol says that when the peer tries to negotiate the same magic number, a NAK should be sent and a new magic number should be chosen. During the period that the server port has ECHO turned on, the client ppp(8) sends LCP packets, sees the same magic in the reflected packet and NAKs it. It also sees the NAK reflect (which also means ppp(8) must change its magic). This produces a potentially enormous number of magic number changes, all of which are happily piling into the server's tty buffer. As soon as ppp(8) starts on the server, it is flooded with magic number changes and almost immediately decides it has tried enough to negotiate LCP and gives up. Meanwhile, the client, who no longer sees the reflections, becomes happy just in time to see a hangup from the server. This can be avoided by allowing the peer to start
negotiating with the following line in
set openmode passive This tells ppp(8) to wait for the server to initiate LCP negotiations. Some servers however may never initiate negotiations. If this is the case, you can do something like: set openmode active 3 This tells ppp(8) to be passive for 3 seconds, and then to start sending LCP requests. If the peer starts sending requests during this period, ppp(8) will immediately respond rather than waiting for the full 3 second period. | |
13.12. | LCP negotiations continue until the connection is closed. What is wrong? |
There is currently an implementation mis-feature in ppp(8) where it does not associate LCP, CCP & IPCP responses with their original requests. As a result, if one PPP implementation is more than 6 seconds slower than the other side, the other side will send two additional LCP configuration requests. This is fatal. Consider two implementations, This goes on until one side figures out that they are getting nowhere and gives up. The best way to avoid this is to configure one side to
be set openmode passive Care should be taken with this option. You should also use this command to limit the amount of time that ppp(8) waits for the peer to begin negotiations: set stopped N Alternatively, the following command (where
set openmode active N Check the manual page for details. | |
13.13. | Why does ppp(8) lock up when I shell out to test it? |
When you execute the To execute commands like this, use
| |
13.14. | Why does ppp(8) over a null-modem cable never exit? |
There is no way for ppp(8) to automatically determine that a direct connection has been dropped. This is due to the lines that are used in a null-modem serial cable. When using this sort of connection, LQR should always be enabled with the following line: enable lqr LQR is accepted by default if negotiated by the peer. | |
13.15. | Why does ppp(8) dial for no reason in
If ppp(8) is dialing unexpectedly, you must determine the cause, and set up Dial filters (dfilters) to prevent such dialing. To determine the cause, use the following line: set log +tcp/ip This will log all traffic through the connection. The next time the line comes up unexpectedly, you will see the reason logged with a convenient timestamp next to it. You can now disable dialing under these circumstances. Usually, this sort of problem arises due to DNS lookups. To prevent DNS lookups from establishing a connection (this will not prevent ppp(8) from passing the packets through an established connection), use the following: set dfilter 1 deny udp src eq 53set dfilter 2 deny udp dst eq 53set dfilter 3 permit 0/0 0/0 This is not always suitable, as it will effectively break your demand-dial capabilities — most programs will need a DNS lookup before doing any other network related things. In the DNS case, you should try to determine what is
actually trying to resolve a host name. A lot of the time,
sendmail(8) is the culprit. You should make sure that
you tell sendmail not to do any
DNS lookups in its configuration file. See the section on
using email with a dialup connection
in the FreeBSD Handbook for details on how to create your own
configuration file and what should go into it. You may also
want to add the following line to
define(`confDELIVERY_MODE', `d')dnl This will make sendmail queue
everything until the queue is run (usually, sendmail is
run with | |
13.16. | What do these CCP errors mean? |
I keep seeing the following errors in my log file: CCP: CcpSendConfigReqCCP: Received Terminate Ack (1) state = Req-Sent (6) This is because ppp(8) is trying to negotiate Predictor1 compression, and the peer does not want to negotiate any compression at all. The messages are harmless, but if you wish to remove them, you can disable Predictor1 compression locally too: disable pred1 | |
13.17. | Why does ppp(8) not log my connection speed? |
To log all lines of your modem "conversation", you must enable the following: set log +connect This will make ppp(8) log everything up until the last requested "expect" string. If you wish to see your connect speed and are using PAP
or CHAP (and therefore do not have anything to
"chat" after the CONNECT in the dial script
— no set dial "ABORT BUSY ABORT NO\\sCARRIER TIMEOUT 4 \ \"\" ATZ OK-ATZ-OK ATDT\\T TIMEOUT 60 CONNECT \\c \\n" Here, we get our CONNECT, send nothing, then expect a line-feed, forcing ppp(8) to read the whole CONNECT response. | |
13.18. | Why does ppp(8) ignore the |
The ppp utility parses each
line in your config files so that it can interpret strings
such as When the chat interpreter parses each argument, it
re-interprets the argument to find any special
escape sequences such as If you wish to actually send a set dial "\"\" ATZ OK-ATZ-OK AT\\\\X OK" It will result in the following sequence: ATZOKAT\XOK Or: set phone 1234567set dial "\"\" ATZ OK ATDT\\T" It will result in the following sequence: ATZOKATDT1234567 | |
13.19. | Why does ppp(8) get a Segmentation
fault, but I see no
The ppp utility (or any other
program for that matter) should never dump core. Because
ppp(8) runs setuid (with an effective user ID of
# cd /usr/src/usr.sbin/ppp# echo STRIP= >> /etc/make.conf# echo CFLAGS+=-g >> /etc/make.conf# make install clean You will now have a debuggable version of ppp(8)
installed. You will have to be Now, if and when ppp(8) receives the segmentation
violation, it will dump a core file called
% su# gdb /usr/sbin/ppp ppp.core(gdb) bt.....(gdb) f 0....(gdb) i args....(gdb) l..... All of this information should be given alongside your question, making it possible to diagnose the problem. If you are familiar with gdb(1), you may wish to find out some other bits and pieces such as what actually caused the dump or the addresses and values of the relevant variables. | |
13.20. | Why does the process that forces a dial in
This was a known problem with ppp(8) set up to
negotiate a dynamic local IP number with the peer in
The problem was that when that initial program calls connect(2), the IP number of the tun(4) interface is assigned to the socket endpoint. The kernel creates the first outgoing packet and writes it to the tun(4) device. ppp(8) then reads the packet and establishes a connection. If, as a result of ppp(8)'s dynamic IP assignment, the interface address is changed, the original socket endpoint will be invalid. Any subsequent packets sent to the peer will usually be dropped. Even if they are not, any responses will not route back to the originating machine as the IP number is no longer owned by that machine. There are several theoretical ways to approach this problem. It would be nicest if the peer would re-assign the same IP number if possible. The current version of ppp(8) does this, but most other implementations do not. The easiest method from our side would be to never
change the tun(4) interface IP number, but instead to
change all outgoing packets so that the source IP number is
changed from the interface IP to the negotiated IP on the
fly. This is essentially what the
Another alternative (and probably the most reliable)
would be to implement a system call that changes all bound
sockets from one IP to another. ppp(8) would use this
call to modify the sockets of all existing programs when a
new IP number is negotiated. The same system call could be
used by DHCP clients when they are forced
to call the Yet another possibility is to allow an interface to be
brought up without an IP number. Outgoing packets would be
given an IP number of | |
13.21. | Why do most games not work with the
The reason games and the like do not work when libalias(3) is in use is that the machine on the outside will try to open a connection or send (unsolicited) UDP packets to the machine on the inside. The NAT software does not know that it should send these packets to the interior machine. To make things work, make sure that the only thing
running is the software that you are having problems with,
then either run tcpdump(1) on the tun(4) interface
of the gateway or enable ppp(8) TCP/IP logging
( When you start the offending software, you should see
packets passing through the gateway machine. When something
comes back from the outside, it will be dropped (that is the
problem). Note the port number of these packets then shut
down the offending software. Do this a few times to see if
the port numbers are consistent. If they are, then the
following line in the relevant section of
nat port proto internalmachine:port port where You will not be able to use the software on other machines without changing the above command, and running the software on two internal machines at the same time is out of the question — after all, the outside world is seeing your entire internal network as being just a single machine. If the port numbers are not consistent, there are three more options:
| |
13.22. | What are FCS errors? |
FCS stands for Frame Check Sequence. Each
PPP packet has a checksum attached to ensure that the data
being received is the data being sent. If the FCS of an
incoming packet is incorrect, the packet is dropped and the
HDLC FCS count is increased. The HDLC error values can be
displayed using the If your link is bad (or if your serial driver is dropping packets), you will see the occasional FCS error. This is not usually worth worrying about although it does slow down the compression protocols substantially. If you have an external modem, make sure your cable is properly shielded from interference — this may eradicate the problem. If your link freezes as soon as you have connected and
you see a large number of FCS errors, this may be because your
link is not 8-bit clean. Make sure your modem is not using
software flow control (XON/XOFF). If your datalink
must use software flow control, use the
command Another reason for seeing too many FCS errors may be
that the remote end has stopped talking
PPP. You may want to enable
If nothing in your log file indicates why the link might have been terminated, you should ask the remote administrator (your ISP?) why the session was terminated. | |
13.23. | None of this helps — I am desperate! What can I do? |
If all else fails, send as much information as you can,
including your config files, how you are starting
ppp(8), the relevant parts of your log file and the
output of |
This section answers common questions about serial communications with FreeBSD. PPP is covered in the Networking section.
14.1. | Which multi-port serial cards are supported by FreeBSD? |
There is a list of these in the Serial Communications chapter of the handbook. Most multi-port PCI cards that are based on 16550 or clones are supported with no extra effort. Some unnamed clone cards have also been known to work, especially those that claim to be AST compatible. Check uart(4) and sio(4) to get more information on configuring such cards. | |
14.2. | How do I get the boot: prompt to show on the serial console? |
14.3. | How do I tell if FreeBSD found my serial ports or modem cards? |
As the FreeBSD kernel boots, it will probe for the serial ports in your system for which the kernel was configured. You can either watch your system closely for the messages it prints or run this command after your system is up and running: % dmesg | grep -E "^sio[0-9]" Here is some example output from the above command: sio0: <16550A-compatible COM port> port 0x3f8-0x3ff irq 4 flags 0x10 on acpi0sio0: type 16550Asio1: <16550A-compatible COM port> port 0x2f8-0x2ff irq 3 on acpi0sio1: type 16550A This shows two serial ports. The first is on
IRQ 4, is using port address The | |
14.4. | How do I access the serial ports on FreeBSD? |
The third serial port, You use
| |
14.5. | How do I enable support for a multiport serial card? |
Again, the section on kernel configuration provides information about configuring your kernel. For a multiport serial card, place an sio(4) line for each serial port on the card in the device.hints(5) file. But place the IRQ specifiers on only one of the entries. All of the ports on the card should share one IRQ. For consistency, use the last serial port to specify the IRQ. Also, specify the following option in the kernel configuration file: options COM_MULTIPORT The following hint.sio.4.at="isa"hint.sio.4.port="0x2a0"hint.sio.4.flags="0x701"hint.sio.5.at="isa"hint.sio.5.port="0x2a8"hint.sio.5.flags="0x701"hint.sio.6.at="isa"hint.sio.6.port="0x2b0"hint.sio.6.flags="0x701"hint.sio.7.at="isa"hint.sio.7.port="0x2b8"hint.sio.7.flags="0x701"hint.sio.7.irq="12" The flags indicate that the master port has minor number
| |
14.6. | Can I set the default serial parameters for a port? |
See the Serial Communications section in the FreeBSD Handbook. | |
14.7. | How can I enable dialup logins on my modem? |
Please read the section about Dial-in Services in the FreeBSD Handbook. | |
14.8. | How can I connect a dumb terminal to my FreeBSD box? |
You can find this information in the Terminals section of the FreeBSD Handbook. | |
14.9. | Why can I not run |
On your system, the programs tip(1) and cu(1)
can only access the Alternatively, you can let everyone on your system run tip(1) and cu(1) by typing: # chmod 4511 /usr/bin/cu# chmod 4511 /usr/bin/tip |
15.1. | FreeBSD uses a lot of swap space even when the computer has free memory left. Why? | ||||||
FreeBSD will proactively move entirely idle, unused pages of main memory into swap in order to make more main memory available for active use. This heavy use of swap is balanced by using the extra free memory for cacheing. Note that while FreeBSD is proactive in this regard, it does not arbitrarily decide to swap pages when the system is truly idle. Thus you will not find your system all paged out when you get up in the morning after leaving it idle overnight. | |||||||
15.2. | Why does | ||||||
The simple answer is that free memory is wasted memory.
Any memory that your programs do not actively allocate is
used within the FreeBSD kernel as disk cache. The values shown
by top(1) labeled as | |||||||
15.3. | Why will | ||||||
Symlinks do not have permissions, and by default,
chmod(1) will follow symlinks to change the
permissions on the source file, if possible. So if you have a file,
% chmod g-w bar However, the permissions on When changing modes of the file hierarchies rooted in the
files instead of the files themselves,
you have to use either Warning:
% chmod 555 foo/ With the trailing slash, chmod(1) will follow the
symlink, | |||||||
15.4. | Can I run DOS binaries under FreeBSD? | ||||||
Yes, you can use emulators/doscmd, a DOS emulation program, available in the FreeBSD Ports Collection. If doscmd will not suffice, the add-on utility emulators/pcemu emulates an 8088 and enough BIOS services to run many DOS text mode applications. It requires the X Window System. You may also try emulators/dosbox from the FreeBSD Ports Collection. The main focus of this application is emulating old DOS games using the local file system for files. | |||||||
15.5. | What do I need to do to translate a FreeBSD document into my native language? | ||||||
See the Translation FAQ in the FreeBSD Documentation Project Primer. | |||||||
15.6. | Why does my email to any address at | ||||||
Other advice to help your mail reach its destination include:
If you still have trouble with email infrastructure at
| |||||||
15.7. | Where can I find a free FreeBSD account? | ||||||
While FreeBSD does not provide open access to any of their servers, others do provide open access UNIX® systems. The charge varies and limited services may be available. Arbornet, Inc, also known as M-Net, has been providing open access to UNIX® systems since 1983. Starting on an Altos running System III, the site switched to BSD/OS in 1991. In June of 2000, the site switched again to FreeBSD. M-Net can be accessed via telnet and SSH and provides basic access to the entire FreeBSD software suite. However, network access is limited to members and patrons who donate to the system, which is run as a non-profit organization. M-Net also provides an bulletin board system and interactive chat. | |||||||
15.8. | What is the cute little red guy's name? | ||||||
He does not have one, and is just called "the BSD daemon". If you insist upon using a name, call him "beastie". Note that "beastie" is pronounced "BSD". You can learn more about the BSD daemon on his home page. | |||||||
15.9. | Can I use the BSD daemon image? | ||||||
Perhaps. The BSD daemon is copyrighted by Marshall Kirk McKusick. You will want to check his Statement on the Use of the BSD Daemon Figure for detailed usage terms. In summary, you are free to use the image in a tasteful
manner, for personal use, so long as appropriate credit is
given. If you want to use him commercially, you must
contact Kirk McKusick | |||||||
15.10. | Do you have any BSD daemon images I could use? | ||||||
You will find eps and Xfig drawings under
| |||||||
15.11. | I have seen an acronym or other term on the mailing lists and I do not understand what it means. Where should I look? | ||||||
Please see the FreeBSD Glossary. | |||||||
15.12. | Why should I care what color the bikeshed is? | ||||||
The really, really short answer is that you should not. The somewhat longer answer is that just because you are capable of building a bikeshed does not mean you should stop others from building one just because you do not like the color they plan to paint it. This is a metaphor indicating that you need not argue about every little feature just because you know enough to do so. Some people have commented that the amount of noise generated by a change is inversely proportional to the complexity of the change. The longer and more complete answer is that after a very
long argument about whether sleep(1) should take
fractional second arguments, Poul-Henning Kamp
16.1. | How cool is FreeBSD? |
Q. Has anyone done any temperature testing while running FreeBSD? I know Linux® runs cooler than DOS, but have never seen a mention of FreeBSD. It seems to run really hot. A. No, but we have done numerous taste tests on blindfolded volunteers who have also had 250 micrograms of LSD-25 administered beforehand. 35% of the volunteers said that FreeBSD tasted sort of orange, whereas Linux® tasted like purple haze. Neither group mentioned any significant variances in temperature. We eventually had to throw the results of this survey out entirely anyway when we found that too many volunteers were wandering out of the room during the tests, thus skewing the results. We think most of the volunteers are at Apple now, working on their new "scratch and sniff" GUI. It is a funny old business we are in! Seriously, FreeBSD uses the HLT (halt) instruction when the system is idle thus lowering its energy consumption and therefore the heat it generates. Also if you have ACPI (Advanced Configuration and Power Interface) configured, then FreeBSD can also put the CPU into a low power mode. | |
16.2. | Who is scratching in my memory banks?? |
Q. Is there anything "odd" that FreeBSD does when compiling the kernel which would cause the memory to make a scratchy sound? When compiling (and for a brief moment after recognizing the floppy drive upon startup, as well), a strange scratchy sound emanates from what appears to be the memory banks. A. Yes! You will see frequent references to "daemons" in the BSD documentation, and what most people do not know is that this refers to genuine, non-corporeal entities that now possess your computer. The scratchy sound coming from your memory is actually high-pitched whispering exchanged among the daemons as they best decide how to deal with various system administration tasks. If the noise gets to you, a good
| |
16.3. | How many FreeBSD hackers does it take to change a lightbulb? |
One thousand, one hundred and sixty-nine: Twenty-three to complain to -CURRENT about the lights being out; Four to claim that it is a configuration problem, and that such matters really belong on -questions; Three to submit PRs about it, one of which is misfiled under doc and consists only of "it's dark"; One to commit an untested lightbulb which breaks buildworld, then back it out five minutes later; Eight to flame the PR originators for not including patches in their PRs; Five to complain about buildworld being broken; Thirty-one to answer that it works for them, and they must have updated at a bad time; One to post a patch for a new lightbulb to -hackers; One to complain that he had patches for this three years ago, but when he sent them to -CURRENT they were just ignored, and he has had bad experiences with the PR system; besides, the proposed new lightbulb is non-reflexive; Thirty-seven to scream that lightbulbs do not belong in the base system, that committers have no right to do things like this without consulting the Community, and WHAT IS -CORE DOING ABOUT IT!? Two hundred to complain about the color of the bicycle shed; Three to point out that the patch breaks style(9); Seventeen to complain that the proposed new lightbulb is under GPL; Five hundred and eighty-six to engage in a flame war about the comparative advantages of the GPL, the BSD license, the MIT license, the NPL, and the personal hygiene of unnamed FSF founders; Seven to move various portions of the thread to -chat and -advocacy; One to commit the suggested lightbulb, even though it shines dimmer than the old one; Two to back it out with a furious flame of a commit message, arguing that FreeBSD is better off in the dark than with a dim lightbulb; Forty-six to argue vociferously about the backing out of the dim lightbulb and demanding a statement from -core; Eleven to request a smaller lightbulb so it will fit their Tamagotchi if we ever decide to port FreeBSD to that platform; Seventy-three to complain about the SNR on -hackers and -chat and unsubscribe in protest; Thirteen to post "unsubscribe", "How do I unsubscribe?", or "Please remove me from the list", followed by the usual footer; One to commit a working lightbulb while everybody is too busy flaming everybody else to notice; Thirty-one to point out that the new lightbulb would shine 0.364% brighter if compiled with TenDRA (although it will have to be reshaped into a cube), and that FreeBSD should therefore switch to TenDRA instead of GCC; One to complain that the new lightbulb lacks fairings; Nine (including the PR originators) to ask "what is MFC?"; Fifty-seven to complain about the lights being out two weeks after the bulb has been changed. Nik Clayton I was laughing quite hard at this. And then I thought, "Hang on, shouldn't there be '1 to document it.' in that list somewhere?" And then I was enlightened :-) Thomas Abthorpe | |
16.4. | Where does data written to
It goes into a special data sink in the CPU where it is
converted to heat which is vented through the heatsink / fan
assembly. This is why CPU cooling is increasingly
important; as people get used to faster processors, they
become careless with their data and more and more of it ends
up in Paul Robinson adds: There are other methods. As every good sysadmin knows, it is part of standard practice to send data to the screen of interesting variety to keep all the pixies that make up your picture happy. Screen pixies (commonly mis-typed or re-named as "pixels") are categorized by the type of hat they wear (red, green or blue) and will hide or appear (thereby showing the color of their hat) whenever they receive a little piece of food. Video cards turn data into pixie-food, and then send them to the pixies — the more expensive the card, the better the food, so the better behaved the pixies are. They also need constant stimulation — this is why screen savers exist. To take your suggestions further, you could just throw the random data to console, thereby letting the pixies consume it. This causes no heat to be produced at all, keeps the pixies happy and gets rid of your data quite quickly, even if it does make things look a bit messy on your screen. Incidentally, as an ex-admin of a large ISP who experienced many problems attempting to maintain a stable temperature in a server room, I would strongly discourage people sending the data they do not want out to the network. The fairies who do the packet switching and routing get annoyed by it as well. | |
16.5. | My colleague sits at the computer too much, how can I prank her? |
Install games/sl and wait
for her to mistype |
17.1. | How can I learn more about FreeBSD's internals? |
See the FreeBSD Architecture Handbook. Additionally, much general UNIX® knowledge is directly applicable to FreeBSD. | |
17.2. | How can I contribute to FreeBSD? |
Please see the article on Contributing to FreeBSD for specific advice on how to do this. Assistance is more than welcome! | |
17.3. | What are snapshots and releases? |
There are currently 4 active/semi-active branches in the FreeBSD Subversion Repository. (Earlier branches are only changed very rarely, which is why there are only 4 active branches of development):
Right now, -CURRENT is the
11. | |
17.4. | Can I follow -CURRENT with limited Internet access? |
Yes, you can do this without downloading the whole source tree by using the CTM facility. | |
17.5. | I have written a kernel extension, who do I send it to? |
Please take a look at the article on Contributing to FreeBSD to learn how to submit code. And thanks for the thought! | |
17.6. | How can I make the most of the data I see when my kernel panics? |
Here is typical kernel panic: Fatal trap 12: page fault while in kernel modefault virtual address = 0x40fault code = supervisor read, page not presentinstruction pointer = 0x8:0xf014a7e5stack pointer = 0x10:0xf4ed6f24frame pointer = 0x10:0xf4ed6f28code segment = base 0x0, limit 0xfffff, type 0x1b = DPL 0, pres 1, def32 1, gran 1processor eflags = interrupt enabled, resume, IOPL = 0current process = 80 (mount)interrupt mask =trap number = 12panic: page fault When you see a message like this, it is not enough to
just reproduce it and send it in. The instruction pointer
value is important;
unfortunately, it is also configuration dependent. In other
words, the value varies depending on the exact kernel image
that you are using. If you are using a
What you should do is this:
However, the best way to track down the cause of a panic is by capturing a crash dump, then using kgdb(1) to generate a stack trace on the crash dump. In any case, the method is this:
Note:If you do not use the The make(1) process will have built two kernels.
To make sure you capture a crash dump, you need edit
Note:FreeBSD crash dumps are usually the same size as the
physical RAM size of your machine. That is, if you have
512 MB of RAM, you will get a 512 MB crash dump.
Therefore you must make sure there is enough space in
Once you have recovered the crash dump, you can get a stack trace with kgdb(1) as follows: % kgdb /usr/obj/usr/src/sys/MYKERNEL/kernel.debug /var/crash/vmcore.0(kgdb) backtrace Note that there may be several screens worth of information; ideally you should use script(1) to capture all of them. Using the unstripped kernel image with all the debug symbols should show the exact line of kernel source code where the panic occurred. Usually you have to read the stack trace from the bottom up to trace the exact sequence of events that lead to the crash. You can also use kgdb(1) to print out the contents of various variables or structures to examine the system state at the time of the crash. Tip:Now, if you are really insane and have a second computer, you can also configure kgdb(1) to do remote debugging such that you can use kgdb(1) on one system to debug the kernel on another system, including setting breakpoints, single-stepping through the kernel code, just like you can do with a normal user-mode program. Note:If you have | |
17.7. | Why has |
The ELF toolchain does not, by default, make the symbols
defined in an executable visible to the dynamic linker.
Consequently If you want to search, using
| |
17.8. | How can I increase or reduce the kernel address space on i386? |
By default, the kernel address space is 1 GB (2 GB for PAE) for i386. If you run a network-intensive server (e.g., a FTP or HTTP server), or you want to use ZFS, you might find that is not enough. Add the following line to your kernel configuration file to increase available space and rebuild your kernel: options KVA_PAGES=N To find the correct value of
This innocent little Frequently Asked Questions document has been written, rewritten, edited, folded, spindled, mutilated, eviscerated, contemplated, discombobulated, cogitated, regurgitated, rebuilt, castigated, and reinvigorated over the last decade, by a cast of hundreds if not thousands. Repeatedly.
We wish to thank every one of the people responsible, and we encourage you to join them in making this FAQ even better.
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