CODEWITHSUNDEEP
linuxbashsignals
Mustafa
Mustafa

Reputation: 10413

SIGTERM signal not caught when the last process is tail

I have the following script, which has tail --pid=${somepid} -f ${mylogs}. I want to catch SIGTERM and do some graceful shutdown on that PID, because that process does not understand SIGTERM and dies painfully.

echo "pid: $$"

trap_with_arg() {
    func="$1" ; shift
    for sig ; do
        trap "$func $sig" "$sig"
    done
}

func_trap() {
    echo Trapped: $1
}

trap_with_arg func_trap INT TERM EXIT STOP
tail -f /dev/null

When I use kill -15 ${bashpid} from another terminal, the trapped signal is not printed until I use CTRL+C. When the last command is not a process, but rather a read which is a shell built-in, the trapped signals are printed immediately. Why is this the case? If I do the following it works:

tail -f /dev/null &
wait $!

Upvotes: 3

Views: 1342

Answers (1)

Maxim Egorushkin
Maxim Egorushkin

Reputation: 136208

If you have a look at man bash:

If bash is waiting for a command to complete and receives a signal for which a trap has been set, the trap will not be executed until the command completes. When bash is waiting for an asynchronous command via the wait builtin, the reception of a signal for which a trap has been set will cause the wait builtin to return immediately with an exit status greater than 128, immediately after which the trap is executed.

Upvotes: 8

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