Chapter 5. Kernel Parameters
Chapter 5. Kernel Parameters You can modify the kernel behaviour with kernel parameters. Parameter Description BridgeNfCallArpTables Configures sysctl net.bridge.bridge-nf-call-arptables key. The default value is 1 . BridgeNfCallIp6Tables Configures sysctl net.bridge.bridge-nf-call-ip6tables key. The default value is 1 . BridgeNfCallIpTables Configures sysctl net.bridge.bridge-nf-call-iptables key. The default value is 1 . ExtraKernelModules Hash of extra kernel modules to load. ExtraKernelPackages List of extra kernel related packages to install. ExtraSysctlSettings Hash of extra sysctl settings to apply. FsAioMaxNumber The kernel allocates aio memory on demand, and this number limits the number of parallel aio requests; the only drawback of a larger limit is that a malicious guest could issue parallel requests to cause the kernel to set aside memory. Set this number at least as large as 128 * (number of virtual disks on the host) Libvirt uses a default of 1M requests to allow 8k disks, with at most 64M of kernel memory if all disks hit an aio request at the same time. The default value is 0 . InotifyInstancesMax Configures sysctl fs.inotify.max_user_instances key. The default value is 1024 . InotifyIntancesMax Configures sysctl fs.inotify.max_user_instances key. The default value is 1024 . KernelDisableIPv6 Configures sysctl net.ipv6.{default/all}.disable_ipv6 keys. The default value is 0 . KernelIpForward Configures net.ipv4.ip_forward key. The default value is 1 . KernelIpNonLocalBind Configures net.ipv{4,6}.ip_nonlocal_bind key. The default value is 1 . KernelIpv4ConfAllRpFilter Configures the net.ipv4.conf.all.rp_filter key. The default value is 1 . KernelIpv6ConfAllForwarding Configures the net.ipv6.conf.all.forwarding key. The default value is 0 . KernelPidMax Configures sysctl kernel.pid_max key. The default value is 1048576 . NeighbourGcThreshold1 Configures sysctl net.ipv4.neigh.default.gc_thresh1 value. This is the minimum number of entries to keep in the ARP cache. The garbage collector will not run if there are fewer than this number of entries in the cache. The default value is 1024 . NeighbourGcThreshold2 Configures sysctl net.ipv4.neigh.default.gc_thresh2 value. This is the soft maximum number of entries to keep in the ARP cache. The garbage collector will allow the number of entries to exceed this for 5 seconds before collection will be performed. The default value is 2048 . NeighbourGcThreshold3 Configures sysctl net.ipv4.neigh.default.gc_thresh3 value. This is the hard maximum number of entries to keep in the ARP cache. The garbage collector will always run if there are more than this number of entries in the cache. The default value is 4096 .