I would like to run the simple shell command
echo 1 > /proc/sys/kernel/sysrq at each boot, to enable the sysrq keys. When in boot should this be done, and where should I put a script to do it?
Depends on distros.
If you are on Debian-derived distros, there are at least two proper places, /etc/rc.local and crontab. You may invoke crontab as root,
and then insert this line
my_command is an executable file (
chmod 755 my_command).
Alternatively, you may place a line like this
in /etc/rc.local, and this will be executed last. In any case, pls do remember you are using root environment, not yours. Also for this reason, it is best to use absolute paths.
If you are on a systemd distro (Arch Linux, Fedora 19,...) the first option (crontab) is still valid, while the second one (/etc/rc.local) does not exist any longer. In this case, you should learn how to start a service to be run by
systemctl, but this may be more than you bargained for with your simple question.
If your system is running a version of
cron that supports it (specifically Vixie cron), you can use
@reboot in a cron job.
This is one of 8 special strings that it supports.
crontab(5) man page (from my Ubuntu 12.04 system):
Instead of the first five fields, one of eight special strings may appear:
string meaning ------ ------- @reboot Run once, at startup. @yearly Run once a year, "0 0 1 1 *". @annually (same as @yearly) @monthly Run once a month, "0 0 1 * *". @weekly Run once a week, "0 0 * * 0". @daily Run once a day, "0 0 * * *". @midnight (same as @daily) @hourly Run once an hour, "0 * * * *".
Please note that startup, as far as
@rebootis concerned, is the time when the cron(8) daemon startup. In particular, it may be before some system daemons, or other facilities, were startup. This is due to the boot order sequence of the machine.
This is far from being the only way to run something at boot time, but it's an alternative.
Pretty much all variants of Linux (going back a long, long time) have a file /etc/rc.local which runs on startup - you can just add the command to it.
That said, you don't even need to do that. The "correct" way would be to modify / add the line kernel.sysrq = 1 into /etc/sysctl.conf