Changing user in a script?

Question

I am trying to change user in order to execute a specific command during startup. It fails silently and apparently the userchange isn't carried out as I can tell that the command isn't executed.

What am I doing wrong in my below shown initscript?

respawn
console none

start on startup
stop on shutdown

script
  su -u anotheruser -c "myCommand" >> "myLogfile.log"
end script

Answer 1

I'm assuming you are running recent version of ubuntu or a distribution based on upstart. You can check /var/log/daemon.log for errors.

The standard su takes the syntax su [options] [username]. Checkout man 1 su. You might want to try :

su -c "myCommand" anotheruser >> "myLogfile.log"

Also, a couple of things would happen (mostly not desirable)

1. myLogfile.log would be owned by root.
2. myLogfile.log would be created on / (root directory) if you don't use an absolute path like /tmp/myLogfile.log (because upstart runs with pwd set to /).

If you want the file to be owned by anotheruser you might switch the command to.

su -c "myCommand >> /tmp/myLogfile.log" anotheruser

This might cause problems if you have leftover myLogfile.log owned by root from earlier runs or if have not changed myLogfile.log to something like /tmp/myLogfile.log (normally, regular users can't create files on root dir /).

Answer 2

It looks like you've mixed up the syntax of su and sudo.

su -c 'mycommand' anotheruser
sudo -u anotheruser 'mycommand'