Linux Boot Configuration
In no way intended to be a complete list - but as I come up with boot-time config needs that I don't know already I'll try to add notes on them here.
IO Scheduler
The IO Scheduler can be set at run-time very easily through sysfs - for example:
example:~# cat /sys/block/sda/queue/scheduler noop anticipatory [deadline] cfq example:~# echo cfq > /sys/block/sda/queue/scheduler example:~# cat /sys/block/sda/queue/scheduler noop anticipatory deadline [cfq]
See also: http://www.kernel.org/doc/Documentation/block/switching-sched.txt
Details on the various schedulers can be read here: I/O_scheduling
Unfortunately I've not found a way to set a per-device IO scheduler at boot time - though it would be simple enough to script up pseudo-service or @reboot cron job to do this.
It's possible to set a kernel default sheduler by adding the "elevator=<scheduler>" option to the kernel parameter in your boot loader. For example - setting the deadline scheduler as default in grub2 (/boot/grub/menu.lst):
title Debian GNU/Linux, kernel 2.6.26-2-686 root (hd0,0) kernel /boot/vmlinuz-2.6.26-2-686 root=/dev/sda1 ro quiet elevator=deadline initrd /boot/initrd.img-2.6.26-2-686
/proc/sys/... settings
As per various comments in LinuxMemoryManagement it's sometimes desirable to change the default configuration of a value that appears under /proc/sys
/proc/sys/ replaces the deprecated sysctl system, but changes for boot time are still placed in the old-style in /etc/sysctl.conf.
For example - setting /proc/sys/vm/dirty_background_ratio at boot time is done by adding this to /etc/sysctl.conf:
vm.dirty_background_ratio = 2