Wolfgang Resch - Notes

Running a command with a timeout

July 24, 2013

I needed to run a command with a timeout (basically to check non-interactively whether passwordless access to a machine was set up) and found the answer in this answer on StackOverflow:

perl -e '$s = shift; $SIG{ALRM} = sub { print STDERR "Timeout!\n"; kill INT => $p }; \
         exec(@ARGV) unless $p = fork; alarm $s; waitpid $p, 0' 1 yes foo

Another great PERL one liner. Basically it sets an alarm, forks a process, and then complains about Timeout if the process does not finish in time. The alarm will be inherited by the forked process.

I used this to check if password less login was working in a makefile with the following script:

#! /bin/bash
perl -e '$s = 2; $SIG{ALRM} = sub { kill INT => $p; exit 1 };
         exec("ssh -q cluster_head_node \"hostname\"") unless $p = fork;
         alarm $s;
         waitpid $p, 0' &> /dev/null
if [[ $? -eq 0 ]];
    echo "OK"
    exit 0
    echo "FAIL"
    exit 1

Update: I realized you can also do this in bash:

possibly_hanging_job & { sleep ${TIMEOUT}; eval 'kill -9 $!' &> /dev/null; }