Bash – Trap does not catch SIGTERM in child script

bashshellsignalstimeouttrap:

I have two scripts. First one is basically wrapper that calls subscript and sets timeout.

#!/bin/bash
# wrapper_script

timeout --signal=SIGTERM 50 main_script.sh

And if execution of main_script.sh takes longer than 50 s, I am trying to catch SIGTERM

#!/bin/bash
# main_script.sh

trap "echo 'Reached time limit'; rm $log_file; exit" SIGHUP SIGINT SIGTERM

I never get message "Reached time limit" printed, child script gets killed, but it does not catch SIGTERM. Do I miss something?

Best Answer

At least in the example you provided, your main_script.sh is going to exit immediately after the trap statement. If I add while :; do :; done to the end of your main_script.sh I get the "Reached time limit"

Related Solutions

Bash – How to Forward SIGTERM to Child in Bash

Try:

#!/bin/bash 

_term() { 
  echo "Caught SIGTERM signal!" 
  kill -TERM "$child" 2>/dev/null
}

trap _term SIGTERM

echo "Doing some initial work...";
/bin/start/main/server --nodaemon &

child=$! 
wait "$child"

Normally, bash will ignore any signals while a child process is executing. Starting the server with & will background it into the shell's job control system, with $! holding the server's PID (to be used with wait and kill). Calling wait will then wait for the job with the specified PID (the server) to finish, or for any signals to be fired.

When the shell receives SIGTERM (or the server exits independently), the wait call will return (exiting with the server's exit code, or with the signal number + 128 in case a signal was received). Afterward, if the shell received SIGTERM, it will call the _term function specified as the SIGTERM trap handler before exiting (in which we do any cleanup and manually propagate the signal to the server process using kill).

Bash – Why is the trap not printing any log message

Part of your problem is that you have the >> trap.log outside the (quoted) command arg, so all you’re getting in the trap.log file is the output from the trap command itself – which is nothing. I’m not sure what you mean by saying “TRAPPED & READY” when your script is terminating, but it looks like what you mean is

trap 'rm -f filename; echo "message" >> trap.log' sigspec …

And I agree with Karlo: if you are “just killing the servers which are being used by the script,” then the script is quite probably exiting (rather than being killed by a signal) and you should use the EXIT (or, equivalently, 0) sigspec (possibly in addition to 1, 2, and 15).

P.S. You don’t need a semicolon (;) at the end of the trap command arg.

Best Answer

Related Solutions

Bash – How to Forward SIGTERM to Child in Bash

Bash – Why is the trap not printing any log message

Related Question