ADB is working, fastboot is not (HTC Desire Z) The adb devices command is working for me, the fastboot devices command is not (Mac OS X Mavericks, SDK downloaded yesterday, phone is a HTC Desire Z):

$ sudo fastboot -i 0x0bb4 -p 0x0c91 devices
$ fastboot -i 0x0bb4 -p 0x0c91 devices
$ fastboot devices
$ adb devices
List of devices attached 
HT0C5RT00804    device
$ adb shell
#


So fastboot doesn't list devices, whatever I try (sudo, or specifying -i and -p options), while ADB works just fine. I found vendor and product IDs via Mac OS X system information. ADB working seems to indicate that communication between my laptop and the phone does work fine.

How can I get fastboot to work?

Background info:

I'm trying to install cyanogenmod on a HTC Desire Z. Part of the procedure I'm following is described here: http://wiki.cyanogenmod.org/w/HTC_Desire_Z:_Firmware_Downgrade_(Gingerbread)

I get stuck at the fastboot oem rebootRUU step:

 $ fastboot oem rebootRUU
 &lt; waiting for device &gt;


(hangs, I gave up after 20 minutes), and I think that is due to fastboot not working. Any other ideas on how to get past this appreciated?
From your first quoted block, I assume your phone is booted up normally (adb devices lists it as "device"). Fastboot cannot find it there. Try adb reboot fastboot, then check again when your device has booted up into fastboot mode.

See also:


How to Boot Android Devices in various modes (Fastboot/Recovery/Download)
fastboot intro (CyanogenMod Wiki)
FastBoot Mode (KingoApp)
Know Your Android Tools: What Is Fastboot &amp; How Do You Use It?
our fastboot tag-wiki