CODEWITHSUNDEEP
linuxshell
user1296013
user1296013

Reputation: 71

Wait for arbitrary process and get its exit code in Linux

Is there a way to wait until a process finishes if I'm not the one who started it?

e.g. if I ran "ps -ef" and pick any PID (assuming I have rights to access process information) - is there a way I can wait until the PID completes and get its exit code?

Upvotes: 7

Views: 2716

Answers (4)

johnlevon
johnlevon

Reputation: 41

If you can live without the exit code:

tail --pid=$pid -f /dev/null

Upvotes: 4

andrew-e
andrew-e

Reputation: 732

You could use strace, which tracks signals and system calls. The following command waits until a program is done, then prints its exit code:

$ strace -e none -e exit_group -p $PID       # process calls exit(1)
Process 23541 attached - interrupt to quit
exit_group(1)                          = ?
Process 23541 detached

$ strace -e none -e exit_group -p $PID       # ^C at the keyboard
Process 22979 attached - interrupt to quit
--- SIGINT (Interrupt) @ 0 (0) ---
Process 22979 detached

$ strace -e none -e exit_group -p $PID       # kill -9 $PID
Process 22983 attached - interrupt to quit
+++ killed by SIGKILL +++

Signals from ^Z, fg and kill -USR1 get printed too. Either way, you'll need to use sed if you want to use the exit code in a shell script.

If that's too much shell code, you can use a program I hacked together in C a while back. It uses ptrace() to catch signals and exit codes of pids. (It has rough edges and may not work in all situations.)

I hope that helps!

Upvotes: 8

Employed Russian
Employed Russian

Reputation: 213386

is there a way I can wait until the PID completes and get its exit code

Yes, if the process is not being ptraced by somebody else, you can PTRACE_ATTACH to it, and get notified about various events (e.g. signals received), and about its exit.

Beware, this is quite complicated to handle properly.

Upvotes: 4

Lee Netherton
Lee Netherton

Reputation: 22482

If you know the process ID you can make use of the wait command which is a bash builtin:

wait PID

You can get the PID of the last command run in bash using $!. Or, you can grep for it with from the output of ps.

In fact, the wait command is a useful way to run parralel command in bash. Here's an example:

# Start the processes in parallel...
./script1.sh 1>/dev/null 2>&1 &
pid1=$!
./script2.sh 1>/dev/null 2>&1 &
pid2=$!
./script3.sh 1>/dev/null 2>&1 &
pid3=$!
./script4.sh 1>/dev/null 2>&1 &
pid4=$!

# Wait for processes to finish...
echo -ne "Commands sent... "
wait $pid1
err1=$?
wait $pid2
err2=$?
wait $pid3
err3=$?
wait $pid4
err4=$?

# Do something useful with the return codes...
if [ $err1 -eq 0 -a $err2 -eq 0 -a $err3 -eq 0 -a $err4 -eq 0 ]
then
    echo "pass"
else
    echo "fail"
fi

Upvotes: -1

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