How to run nohup and write its pid file in a single bash statement
I want to run my script in background and then write its pid file. I am using nohup to do this.
This is what i came up with,
nohup ./myprogram.sh > /dev/null 2>&1 & && echo $! > run.pid
But this gives a syntax error.
The following doesn't give syntax error but the problem is echo $! doesn't write the correct pid since nohup is run in a sub shell
(nohup ./myprogram.sh > /dev/null 2>&1 &) && echo $! > run.pid
Any solutions for this, given i want a single line statement for achieving this?
You already have one ampersand after the redirect which puts your script in background. Therefore you only need to type the desired command after that ampersand, not prefixed by anything else:
nohup ./myprogram.sh > /dev/null 2>&1 & echo $! > run.pid
This should work:
nohup ./myprogram.sh > /dev/null 2>&1 &
echo $! > run.pid
Grigor's answer is correct, but not complete. Getting the pid directly from the nohup command is not the same as getting the pid of your own process.
running ps -ef
:
root 31885 27974 0 12:36 pts/2 00:00:00 sudo nohup ./myprogram.sh
root 31886 31885 25 12:36 pts/2 00:01:39 /path/to/myprogram.sh
To get the pid of your own process, you can use:
nohup ./myprogram.sh > /dev/null 2>&1 & echo $! > run.pid
# allow for a moment to pass
cat run.pid | pgrep -P $!
Note that if you try to run the second command immediately after nohup, the child process will not exist yet.