Command line command to auto-kill a command after a certain amount of time

MacosUnixCommand LineUtilitiesCpu Usage

Macos Problem Overview

I'd like to automatically kill a command after a certain amount of time. I have in mind an interface like this:

% constrain 300 ./foo args

Which would run "./foo" with "args" but automatically kill it if it's still running after 5 minutes.

It might be useful to generalize the idea to other constraints, such as autokilling a process if it uses too much memory.

Are there any existing tools that do that, or has anyone written such a thing?

ADDED: Jonathan's solution is precisely what I had in mind and it works like a charm on linux, but I can't get it to work on Mac OSX. I got rid of the SIGRTMIN which lets it compile fine, but the signal just doesn't get sent to the child process. Anyone know how to make this work on Mac?

[Added: Note that an update is available from Jonathan that works on Mac and elsewhere.]

Macos Solutions

Solution 1 - Macos

GNU Coreutils includes the timeout command, installed by default on many systems.

To watch free -m for one minute, then kill it by sending a TERM signal:

timeout 1m watch free -m

Solution 2 - Macos

Maybe I'm not understanding the question, but this sounds doable directly, at least in bash:

( /path/to/slow command with options ) & sleep 5 ; kill $!

This runs the first command, inside the parenthesis, for five seconds, and then kills it. The entire operation runs synchronously, i.e. you won't be able to use your shell while it is busy waiting for the slow command. If that is not what you wanted, it should be possible to add another &.

The $! variable is a Bash builtin that contains the process ID of the most recently started subshell. It is important to not have the & inside the parenthesis, doing it that way loses the process ID.

Solution 3 - Macos

I've arrived rather late to this party, but I don't see my favorite trick listed in the answers.

Under *NIX, an alarm(2) is inherited across an execve(2) and SIGALRM is fatal by default. So, you can often simply:

$ doalarm () { perl -e 'alarm shift; exec @ARGV' "$@"; } # define a helper function

$ doalarm 300 ./ args

or install a trivial C wrapper to do that for you.

Advantages Only one PID is involved, and the mechanism is simple. You won't kill the wrong process if, for example, ./ exited "too quickly" and its PID was re-used. You don't need several shell subprocesses working in concert, which can be done correctly but is rather race-prone.

Disadvantages The time-constrained process cannot manipulate its alarm clock (e.g., alarm(2), ualarm(2), setitimer(2)), since this would likely clear the inherited alarm. Obviously, neither can it block or ignore SIGALRM, though the same can be said of SIGINT, SIGTERM, etc. for some other approaches.

Some (very old, I think) systems implement sleep(2) in terms of alarm(2), and, even today, some programmers use alarm(2) as a crude internal timeout mechanism for I/O and other operations. In my experience, however, this technique is applicable to the vast majority of processes you want to time limit.

Solution 4 - Macos

I have a program called timeout that does that - written in C, originally in 1989 but updated periodically since then.

Update: this code fails to compile on MacOS X because SIGRTMIN is not defined, and fails to timeout when run on MacOS X because the signal() function there resumes the wait() after the alarm times out - which is not the required behaviour. I have a new version of timeout.c which deals with both these problems (using sigaction() instead of signal()). As before, contact me for a 10K gzipped tar file with the source code and a manual page (see my profile).

@(#)File:           $RCSfile: timeout.c,v $
@(#)Version:        $Revision: 4.6 $
@(#)Last changed:   $Date: 2007/03/01 22:23:02 $
@(#)Purpose:        Run command with timeout monitor
@(#)Author:         J Leffler
@(#)Copyright:      (C) JLSS 1989,1997,2003,2005-07

#define _POSIX_SOURCE       /* Enable kill() in <unistd.h> on Solaris 7 */
#define _XOPEN_SOURCE 500

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include "stderr.h"

#define CHILD       0
#define FORKFAIL    -1

static const char usestr[] = "[-vV] -t time [-s signal] cmd [arg ...]";

#ifndef lint
/* Prevent over-aggressive optimizers from eliminating ID string */
const char jlss_id_timeout_c[] = "@(#)$Id: timeout.c,v 4.6 2007/03/01 22:23:02 jleffler Exp $";
#endif /* lint */

static void catcher(int signum)

int main(int argc, char **argv)
    pid_t   pid;
    int     tm_out;
    int     kill_signal;
    pid_t   corpse;
    int     status;
    int     opt;
    int     vflag = 0;


    opterr = 0;
    tm_out = 0;
    kill_signal = SIGTERM;
    while ((opt = getopt(argc, argv, "vVt:s:")) != -1)
        case 'V':
            err_version("TIMEOUT", &"@(#)$Revision: 4.6 $ ($Date: 2007/03/01 22:23:02 $)"[4]);
        case 's':
            kill_signal = atoi(optarg);
            if (kill_signal <= 0 || kill_signal >= SIGRTMIN)
                err_error("signal number must be between 1 and %d\n", SIGRTMIN - 1);
        case 't':
            tm_out = atoi(optarg);
            if (tm_out <= 0)
                err_error("time must be greater than zero (%s)\n", optarg);
        case 'v':
            vflag = 1;

    if (optind >= argc || tm_out == 0)

    if ((pid = fork()) == FORKFAIL)
        err_syserr("failed to fork\n");
    else if (pid == CHILD)
        execvp(argv[optind], &argv[optind]);
        err_syserr("failed to exec command %s\n", argv[optind]);

    /* Must be parent -- wait for child to die */
    if (vflag)
        err_remark("time %d, signal %d, child PID %u\n", tm_out, kill_signal, (unsigned)pid);
    signal(SIGALRM, catcher);
    alarm((unsigned int)tm_out);
    while ((corpse = wait(&status)) != pid && errno != ECHILD)
        if (errno == EINTR)
            /* Timed out -- kill child */
            if (vflag)
                err_remark("timed out - send signal %d to process %d\n", (int)kill_signal, (int)pid);
            if (kill(pid, kill_signal) != 0)
                err_syserr("sending signal %d to PID %d - ", kill_signal, pid);
            corpse = wait(&status);

    if (vflag)
        if (corpse == (pid_t) -1)
            err_syserr("no valid PID from waiting - ");
            err_remark("child PID %u status 0x%04X\n", (unsigned)corpse, (unsigned)status);

    if (corpse != pid)
        status = 2; /* I don't know what happened! */
    else if (WIFEXITED(status))
        status = WEXITSTATUS(status);
    else if (WIFSIGNALED(status))
        status = WTERMSIG(status);
        status = 2; /* I don't know what happened! */


If you want the 'official' code for 'stderr.h' and 'stderr.c', contact me (see my profile).

Solution 5 - Macos

There is also ulimit, which can be used to limit the execution time available to sub-processes.

ulimit -t 10

Limits the process to 10 seconds of CPU time.

To actually use it to limit a new process, rather than the current process, you may wish to use a wrapper script:

#! /usr/bin/env python

import os
os.system("ulimit -t 10; other-command-here")

other-command can be any tool. I was running a Java, Python, C and Scheme versions of different sorting algorithms, and logging how long they took, whilst limiting execution time to 30 seconds. A Cocoa-Python application generated the various command lines - including the arguments - and collated the times into a CSV file, but it was really just fluff on top of the command provided above.

Solution 6 - Macos

Perl one liner, just for kicks:

perl -e '$s = shift; $SIG{ALRM} = sub { print STDERR "Timeout!\n"; kill INT => $p }; exec(@ARGV) unless $p = fork; alarm $s; waitpid $p, 0' 10 yes foo

This prints 'foo' for ten seconds, then times out. Replace '10' with any number of seconds, and 'yes foo' with any command.

Solution 7 - Macos

The timeout command from Ubuntu/Debian when compiled from source to work on the Mac. Darwin


Solution 8 - Macos

My variation on the perl one-liner gives you the exit status without mucking with fork() and wait() and without the risk of killing the wrong process:

# Usage: secs cmd [ arg ... ]
exec perl -MPOSIX -e '$SIG{ALRM} = sub { print "timeout: @ARGV\n"; kill(SIGTERM, -$$); }; alarm shift; $exit = system @ARGV; exit(WIFEXITED($exit) ? WEXITSTATUS($exit) : WTERMSIG($exit));' "$@"

Basically the fork() and wait() are hidden inside system(). The SIGALRM is delivered to the parent process which then kills itself and its child by sending SIGTERM to the whole process group (-$$). In the unlikely event that the child exits and the child's pid gets reused before the kill() occurs, this will NOT kill the wrong process because the new process with the old child's pid will not be in the same process group of the parent perl process.

As an added benefit, the script also exits with what is probably the correct exit status.

Solution 9 - Macos

( some_slow_task ) & pid=$!
( sleep $TIMEOUT && kill -HUP $pid ) 2>/dev/null & watcher=$!
wait $pid 2>/dev/null && pkill -HUP -P $watcher

The watcher kills the slow task after given timeout; the script waits for the slow task and terminates the watcher.


  • The slow task run more than 2 sec and was terminated

>Slow task interrupted

( sleep 20 ) & pid=$!
( sleep 2 && kill -HUP $pid ) 2>/dev/null & watcher=$!
if wait $pid 2>/dev/null; then
    echo "Slow task finished"
    pkill -HUP -P $watcher
    wait $watcher
    echo "Slow task interrupted"
  • This slow task finished before the given timeout

>Slow task finished

( sleep 2 ) & pid=$!
( sleep 20 && kill -HUP $pid ) 2>/dev/null & watcher=$!
if wait $pid 2>/dev/null; then
    echo "Slow task finished"
    pkill -HUP -P $watcher
    wait $watcher
    echo "Slow task interrupted"

Solution 10 - Macos

Try something like:

# This function is called with a timeout (in seconds) and a pid.
# After the timeout expires, if the process still exists, it attempts
# to kill it.
function timeout() {
    sleep $1
    # kill -0 tests whether the process exists
    if kill -0 $2 > /dev/null 2>&1 ; then
        echo "killing process $2"
        kill $2 > /dev/null 2>&1
        echo "process $2 already completed"

<your command> &
timeout 3 $cpid
wait $cpid > /dev/null 2>&
exit $?

It has the downside that if your process' pid is reused within the timeout, it may kill the wrong process. This is highly unlikely, but you may be starting 20000+ processes per second. This could be fixed.

Solution 11 - Macos

How about using the expect tool?

## run a command, aborting if timeout exceeded, e.g. timed-run 20 CMD ARGS ...
timed-run() {
  # timeout in seconds
  local tmout="$1"
  env CMD_TIMEOUT="$tmout" expect -f - "$@" <<"EOF"
# expect script follows
eval spawn -noecho $argv
set timeout $env(CMD_TIMEOUT)
expect {
   timeout {
      send_error "error: operation timed out\n"
      exit 1

Solution 12 - Macos

pure bash:


if [[ $# < 2 ]]; then
echo "Usage: $0 timeout cmd [options]"
exit 1



sleep $TIMEOUT
kill -9 -$BOSSPID

trap "kill -9 $TIMERPID" EXIT

eval "$@"

eval "$@"

Solution 13 - Macos

I use "timelimit", which is a package available in the debian repository.

Solution 14 - Macos

A slight modification of the perl one-liner will get the exit status right.

perl -e '$s = shift; $SIG{ALRM} = sub { print STDERR "Timeout!\n"; kill INT => $p; exit 77 }; exec(@ARGV) unless $p = fork; alarm $s; waitpid $p, 0; exit ($? >> 8)' 10 yes foo

Basically, exit ($? >> 8) will forward the exit status of the subprocess. I just chose 77 at the exit status for timeout.

Solution 15 - Macos

Isn't there a way to set a specific time with "at" to do this?

$ at 05:00 PM kill -9 $pid

Seems a lot simpler.

If you don't know what the pid number is going to be, I assume there's a way to script reading it with ps aux and grep, but not sure how to implement that.

$   | grep someprogram
tony     11585  0.0  0.0   3116   720 pts/1    S+   11:39   0:00 grep someprogram
tony     22532  0.0  0.9  27344 14136 ?        S    Aug25   1:23 someprogram

Your script would have to read the pid and assign it a variable. I'm not overly skilled, but assume this is doable.


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