Pfthb

I would like to get the PID of a process I start through ssh.

I have a bash script and here is what I wrote:

SSH_COMMAND='ssh'
cmd=`eval $my_cmd`
PROG_CMD="$program $cmd"
$SSH_COMMAND root@server "(nohup $PROG_CMD) & echo "'$!'" > prog.pid"

Note that variables "program" and "my_cmd" are defined in a JSON file (and contain, respectively, my program and the command to start my program).

My program is started on the server exactly the way it is supposed to start but I do not have the correct PID (i.e : the PID of program) in the prog.pid file.

EDIT : I did an echo of the SSH_COMMAND and I got :

 ssh root@server (my_program args > output.log 2>&1 & ) & echo $! > prog.pid

args : arguments of my_program

output.log : log file of my program

Don't use (command &) &. Just use (command) & (or just command &). With (command &) &, Bash needs to fork another sub-shell to run the command so $! would be the PID of the sub-shell other than the command.

See following example:

[STEP 124] # (nohup sleep 1234 > /dev/null 2>&1 &) &
[1] 44420 <=== this is the PID of the sub-shell which died immediately
[STEP 125] #
[1]+ Done ( nohup sleep 1234 > /dev/null 2>&1 & )
[STEP 126] # ps p 44420 <=== as you can see this PID does not exist any more
 PID TTY STAT TIME COMMAND
[STEP 127] # ps -C sleep u
USER PID TTY STAT START TIME COMMAND
root 44421 pts/13 S 17:48 0:00 sleep 1234
[STEP 128] # kill 44421
[STEP 129] #

This would work fine:

[STEP 131] # (nohup sleep 1234 > /dev/null 2>&1) &
[1] 44424 <=== this is the PID of the sleep command
[STEP 132] # ps p 44424 u
USER PID TTY STAT START TIME COMMAND
root 44424 pts/13 S 17:49 0:00 sleep 1234
[STEP 133] #

To write the file prog.pid (with remote pid) on the local machine just put out the redirection from inside quotes

$SSH_COMMAND root@server "(nohup $PROG_CMD) & echo "'$!' > prog.pid

If the pid wanted is ssh local process echo $! must be taken out ssh command

$SSH_COMMAND root@server "(nohup $PROG_CMD)" & echo $! > prog.pid