How to run a command before the machine automatically shutdowns?

Question

How to run a command before the machine automatically shutdowns?

Answer 1

How about to put a script in the correct runlevel? I think runlevel 6 is shutdown, and then the dir to play in is /etc/rc6.d/

Answer 2

cron isn't the tool for this. You need to set up an upstart job which executes during shutdown, preferably declaring a dependency so that it runs before any services it requires shut down. man 5 init for the details on how to properly define a startup or shutdown task; I can't help beyond that without more information, as it depends on what you're trying to do and what other upstart jobs it depends on.

Answer 3

Try this one, replacing $HOME and $PROFILE with vapid values and save it to ~/.init with permission 644.

Before you do anything, make sure there is a line like

firefox /home/your_name/.mozilla/firefox/your_profile.default tmpfs size=128M,noauto,user,exec,uid=1000,gid=100 0 0

in /etc/fstab, where the mount option noauto prevents tmpfs from being auto-mounted, which could be changed to auto to your preference. I leave it there to keep the whole upstart job in integrity.

description     "automatic firefox profile ram caching"

start on started mountall
stop on stopping mountall
env HOME="/home/your_name"
env PROFILE="your_profile.default"

script
if test -z "$(mount | grep -F "${HOME}/.mozilla/firefox/${PROFILE}" )"
then
mount "${HOME}/.mozilla/firefox/${PROFILE}"
fi
end script


post-start script
cd "${HOME}/.mozilla/firefox"
if test -f packed.tar
then
    tar xpf packed.tar
    echo "$(date): firefox profile unpacked to ram" >> unpack.log
else
    tar xpf packed.tar.old
    echo "$(date): backup profile unpacked to ram" >> unpack.log
fi
touch "${PROFILE}/.unpacked"
end script 


pre-stop script
cd "${HOME}/.mozilla/firefox"
if test -f "${PROFILE}/.unpacked"
then
    tar --exclude '.unpacked' -cpf packed.tmp.tar "$PROFILE"
    mv packed.tar packed.tar.old
    mv packed.tmp.tar packed.tar
    rm "$PFORILE/.unpacked"
    echo "$(date) firefox profile packed from ram" >> pack.log
else
    echo ".unpacked is missing. pack current session data to newfile"
    tar -cpf packed-$(date +%Y%m%d%H%M).tar "$PROFILE"
fi
end script

Answer 4

As a simplified version of funicorn's answer.. an upstart job, either in /etc/init/foo.conf or as ~/.init/foo.conf :

start on starting rc RUNLEVEL=6
task
exec myscript

This will run, and block the entire shutdown until "myscript" exits.

That is all you need. Note that the user jobs (~/.init/foo.conf) are a very new feature and on my 12.04 system with ecryptfs /home do not work, so you may just have to put the job in /etc/init.