Timeout a command in bash without unnecessary delay

Question

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

proposes a 1-line method to timeout a long-running command from the bash command line:

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

But it's possible that a given "long-running" command may finish earlier than the timeout.
(Let's call it a "typically-long-running-but-sometimes-fast" command, or tlrbsf for fun.)

So this nifty 1-liner approach has a couple of problems.
First, the sleep isn't conditional, so that sets an undesirable lower bound on the time taken for the sequence to finish. Consider 30s or 2m or even 5m for the sleep, when the tlrbsf command finishes in 2 seconds — highly undesirable.
Second, the kill is unconditional, so this sequence will attempt to kill a non-running process and whine about it.

So...

Is there a way to timeout a typically-long-running-but-sometimes-fast ("tlrbsf") command that

• has a bash implementation (the other question already has Perl and C answers)
• will terminate at the earlier of the two: tlrbsf program termination, or timeout elapsed
• will not kill non-existing/non-running processes (or, optionally: will not complain about a bad kill)
• doesn't have to be a 1-liner
• can run under Cygwin or Linux

... and, for bonus points

• runs the tlrbsf command in the foreground
• any 'sleep' or extra process in the background

such that the stdin/stdout/stderr of the tlrbsf command can be redirected, same as if it had been run directly?

If so, please share your code. If not, please explain why.

I have spent awhile trying to hack the aforementioned example but I'm hitting the limit of my bash skills.

Answer 1

You are probably looking for the timeout command in coreutils. Since it's a part of coreutils, it is technically a C solution, but it's still coreutils. info timeout for more details. Here's an example:

timeout 5 /path/to/slow/command with options

Answer 2

I think this is precisely what you are asking for:

http://www.bashcookbook.com/bashinfo/source/bash-4.0/examples/scripts/timeout3

#!/bin/bash
#
# The Bash shell script executes a command with a time-out.
# Upon time-out expiration SIGTERM (15) is sent to the process. If the signal
# is blocked, then the subsequent SIGKILL (9) terminates it.
#
# Based on the Bash documentation example.

# Hello Chet,
# please find attached a "little easier"  :-)  to comprehend
# time-out example.  If you find it suitable, feel free to include
# anywhere: the very same logic as in the original examples/scripts, a
# little more transparent implementation to my taste.
#
# Dmitry V Golovashkin <Dmitry.Golovashkin@sas.com>

scriptName="${0##*/}"

declare -i DEFAULT_TIMEOUT=9
declare -i DEFAULT_INTERVAL=1
declare -i DEFAULT_DELAY=1

# Timeout.
declare -i timeout=DEFAULT_TIMEOUT
# Interval between checks if the process is still alive.
declare -i interval=DEFAULT_INTERVAL
# Delay between posting the SIGTERM signal and destroying the process by SIGKILL.
declare -i delay=DEFAULT_DELAY

function printUsage() {
    cat <<EOF

Synopsis
    $scriptName [-t timeout] [-i interval] [-d delay] command
    Execute a command with a time-out.
    Upon time-out expiration SIGTERM (15) is sent to the process. If SIGTERM
    signal is blocked, then the subsequent SIGKILL (9) terminates it.

    -t timeout
        Number of seconds to wait for command completion.
        Default value: $DEFAULT_TIMEOUT seconds.

    -i interval
        Interval between checks if the process is still alive.
        Positive integer, default value: $DEFAULT_INTERVAL seconds.

    -d delay
        Delay between posting the SIGTERM signal and destroying the
        process by SIGKILL. Default value: $DEFAULT_DELAY seconds.

As of today, Bash does not support floating point arithmetic (sleep does),
therefore all delay/time values must be integers.
EOF
}

# Options.
while getopts ":t:i:d:" option; do
    case "$option" in
        t) timeout=$OPTARG ;;
        i) interval=$OPTARG ;;
        d) delay=$OPTARG ;;
        *) printUsage; exit 1 ;;
    esac
done
shift $((OPTIND - 1))

# $# should be at least 1 (the command to execute), however it may be strictly
# greater than 1 if the command itself has options.
if (($# == 0 || interval <= 0)); then
    printUsage
    exit 1
fi

# kill -0 pid   Exit code indicates if a signal may be sent to $pid process.
(
    ((t = timeout))

    while ((t > 0)); do
        sleep $interval
        kill -0 $$ || exit 0
        ((t -= interval))
    done

    # Be nice, post SIGTERM first.
    # The 'exit 0' below will be executed if any preceeding command fails.
    kill -s SIGTERM $$ && kill -0 $$ || exit 0
    sleep $delay
    kill -s SIGKILL $$
) 2> /dev/null &

exec "$@"

Answer 3

This solution works regardless of bash monitor mode. You can use the proper signal to terminate your_command

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

The watcher kills your_command after given timeout; the script waits for the slow task and terminates the watcher. Note that wait does not work with processes which are children of a different shell.

Examples:

• your_command runs more than 2 seconds and was terminated

your_command interrupted

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

• your_command finished before the timeout (20 seconds)

your_command finished

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

Answer 4

To timeout the slowcommand after 1 second:

timeout 1 slowcommand || echo "I failed, perhaps due to time out"

To determine whether the command timed out or failed for its own reasons, check whether the status code is 124:

# ping the address 8.8.8.8 for 3 seconds, but timeout after only 1 second
timeout 1 ping 8.8.8.8 -w3
EXIT_STATUS=$?
if [ $EXIT_STATUS -eq 124 ]
then
echo 'Process Timed Out!'
else
echo 'Process did not timeout. Something else went wrong.'
fi
exit $EXIT_STATUS

Note that when the exit status is 124, you don't know whether it timed out due to your timeout command, or whether the command itself terminated due to some internal timeout logic of its own and then returned 124. You can safely assume in either case, though, that a timeout of some kind happened.

Answer 5

There you go:

timeout --signal=SIGINT 10 /path/to/slow command with options

you may change the SIGINT and 10 as you desire ;)

Answer 6

You can do this entirely with bash 4.3 and above:

_timeout() { ( set +b; sleep "$1" & "${@:2}" & wait -n; r=$?; kill -9 `jobs -p`; exit $r; ) }

• Example: _timeout 5 longrunning_command args

• Example: { _timeout 5 producer || echo KABOOM $?; } | consumer

• Example: producer | { _timeout 5 consumer1; consumer2; }

• Example: { while date; do sleep .3; done; } | _timeout 5 cat | less

• Needs Bash 4.3 for wait -n

• Gives 137 if the command was killed, else the return value of the command.

• Works for pipes. (You do not need to go foreground here!)

• Works with internal shell commands or functions, too.

• Runs in a subshell, so no variable export into the current shell, sorry.

If you do not need the return code, this can be made even simpler:

_timeout() { ( set +b; sleep "$1" & "${@:2}" & wait -n; kill -9 `jobs -p`; ) }

Notes:

• Strictly speaking you do not need the ; in ; ), however it makes thing more consistent to the ; }-case. And the set +b probably can be left away, too, but better safe than sorry.

• Except for --forground (probably) you can implement all variants timeout supports. --preserve-status is a bit difficult, though. This is left as an exercise for the reader ;)

This recipe can be used "naturally" in the shell (as natural as for flock fd):

(
set +b
sleep 20 &
{
YOUR SHELL CODE HERE
} &
wait -n
kill `jobs -p`
)

However, as explained above, you cannot re-export environment variables into the enclosing shell this way naturally.

Edit:

Real world example: Time out __git_ps1 in case it takes too long (for things like slow SSHFS-Links):

eval "__orig$(declare -f __git_ps1)" && __git_ps1() { ( git() { _timeout 0.3 /usr/bin/git "$@"; }; _timeout 0.3 __orig__git_ps1 "$@"; ) }

Edit2: Bugfix. I noticed that exit 137 is not needed and makes _timeout unreliable at the same time.

Edit3: git is a die-hard, so it needs a double-trick to work satisfyingly.

Edit4: Forgot a _ in the first _timeout for the real world GIT example.

---

Update 2023-08-06: I found a better way to restrict the runtime of git, so the above is just an example.

The following is no more bash-only as it needs setsid. But I found no way to reliably create process group leaders with just bash idioms, sorry.

This recipe is a bit more difficult to use, but very effective, as it not only kills the child, it also kills everything the child places in the same process group.

I now use following:

__git_ps1() { setsid -w /bin/bash -c 'sleep 1 & . /usr/lib/git-core/git-sh-prompt && __git_ps1 "$@" & wait -n; p=$(/usr/bin/ps --no-headers -opgrp $$) && [ $$ = ${p:-x} ] && /usr/bin/kill -9 0; echo "PGRP mismatch $$ $p" >&2' bash "$@"; }

What it does:

• setsid -w /bin/bash -c 'SCRIPT' bash "$@" runs SCRIPT in a new process group
• sleep 1 & sets the timeout
• . /usr/lib/git-core/git-sh-prompt && __git_ps1 "$@" & runs the git prompt in parallel
  • /usr/lib/git-core/git-sh-prompt is for Ubuntu 22.04, change it if needed
• wait -n; waits for either the sleep or __git_ps1 to return
  • The first one wins
• p=$(/usr/bin/ps --no-headers -opgrp $$) && [ $$ = ${p:-x} ] && is just a safeguard to check setsid worked and we are really a process group leader
  • $$ works here correctly, as we are within single quotes
• kill -9 0 unconditionally kills the entire process group
  • all git that may still execute
  • including the /bin/bash
• echo "PGRP mismatch $$ $p" >&2' is never reached
  • This informs you that either setsid is a fake
  • or something else (kill?) did not work as expected

The safeguard protects against the case that setsid does not work as advertised. Without your current shell might get killed, which would make it impossible to spawn an interactive shell.

If you use the recipe and trust setsid, you probably do not need the safeguard, so setsid is the only non-bash-idiom this needs.

Answer 7

I prefer "timelimit", which has a package at least in debian.

http://devel.ringlet.net/sysutils/timelimit/

It is a bit nicer than the coreutils "timeout" because it prints something when killing the process, and it also sends SIGKILL after some time by default.

Answer 8

See also the http://www.pixelbeat.org/scripts/timeout script the functionality of which has been integrated into newer coreutils

Answer 9

timeout is probably the first approach to try. You may need notification or another command to execute if it times out. After quite a bit of searching and experimenting, I came up with this bash script:

if 
    timeout 20s COMMAND_YOU_WANT_TO_EXECUTE;
    timeout 20s AS_MANY_COMMANDS_AS_YOU_WANT;
then
    echo 'OK'; #if you want a positive response
else
    echo 'Not OK';
    AND_ALTERNATIVE_COMMANDS
fi

Answer 10

Kinda hacky, but it works. Doesn't work if you have other foreground processes (please help me fix this!)

sleep TIMEOUT & SPID=${!}; (YOUR COMMAND HERE; kill ${SPID}) & CPID=${!}; fg 1; kill ${CPID}

Actually, I think you can reverse it, meeting your 'bonus' criteria:

(YOUR COMMAND HERE & SPID=${!}; (sleep TIMEOUT; kill ${SPID}) & CPID=${!}; fg 1; kill ${CPID}) < asdf > fdsa

Answer 11

Simple script with code clarity. Save to /usr/local/bin/run:

#!/bin/bash

# run
# Run command with timeout $1 seconds.

# Timeout seconds
timeout_seconds="$1"
shift

# PID
pid=$$

# Start timeout
(
  sleep "$timeout_seconds"
  echo "Timed out after $timeout_seconds seconds"
  kill -- -$pid &>/dev/null
) &
timeout_pid=$!

# Run
"$@"

# Stop timeout
kill $timeout_pid &>/dev/null

Times out a command that runs too long:

$ run 2 sleep 10
Timed out after 2 seconds
Terminated
$

Ends immediately for a command that completes:

$ run 10 sleep 2
$

Answer 12

If you already know the name of the program (let's assume program) to terminate after the timeout (as an example 3 seconds), I can contribute a simple and somewhat dirty alternative solution:

(sleep 3 && killall program) & ./program

This works perfectly if I call benchmark processes with system calls.

Answer 13

There's also cratimeout by Martin Cracauer (written in C for Unix and Linux systems).

# cf. http://www.cons.org/cracauer/software.html
# usage: cratimeout timeout_in_msec cmd args
cratimeout 5000 sleep 1
cratimeout 5000 sleep 600
cratimeout 5000 tail -f /dev/null
cratimeout 5000 sh -c 'while sleep 1; do date; done'

Answer 14

OS X doesn't use bash 4 yet, nor does it have /usr/bin/timeout, so here's a function that works on OS X without home-brew or macports that is similar to /usr/bin/timeout (based on Tino's answer). Parameter validation, help, usage, and support for other signals are an exercise for reader.

# implement /usr/bin/timeout only if it doesn't exist
[ -n "$(type -p timeout 2>&1)" ] || function timeout { (
    set -m +b
    sleep "$1" &
    SPID=${!}
    ("${@:2}"; RETVAL=$?; kill ${SPID}; exit $RETVAL) &
    CPID=${!}
    wait %1
    SLEEPRETVAL=$?
    if [ $SLEEPRETVAL -eq 0 ] && kill ${CPID} >/dev/null 2>&1 ; then
      RETVAL=124
      # When you need to make sure it dies
      #(sleep 1; kill -9 ${CPID} >/dev/null 2>&1)&
      wait %2
    else
      wait %2
      RETVAL=$?
    fi
    return $RETVAL
) }

Answer 15

Here is a version that does not rely on spawning a child process - I needed a standalone script which embedded this functionality. It also does a fractional poll interval, so you can poll quicker. timeout would have been preferred - but I'm stuck on an old server

# wait_on_command <timeout> <poll interval> command
wait_on_command()
{
    local timeout=$1; shift
    local interval=$1; shift
    $* &
    local child=$!

    loops=$(bc <<< "($timeout * (1 / $interval)) + 0.5" | sed 's/\..*//g')
    ((t = loops))
    while ((t > 0)); do
        sleep $interval
        kill -0 $child &>/dev/null || return
        ((t -= 1))
    done

    kill $child &>/dev/null || kill -0 $child &>/dev/null || return
    sleep $interval
    kill -9 $child &>/dev/null
    echo Timed out
}

slow_command()
{
    sleep 2
    echo Completed normally
}

# wait 1 sec in 0.1 sec increments
wait_on_command 1 0.1 slow_command

# or call an external command
wait_on_command 1 0.1 sleep 10

Answer 16

The timeout command itself has a --foreground option. This lets the command interact with the user "when not running timeout directly from a shell prompt".

timeout --foreground the_command its_options

I think the questioner must have been aware of the very obvious solution of the timeout command, but asked for an alternate solution for this reason. timeout did not work for me when I called it using popen, i.e. 'not directly from the shell'. However, let me not assume that this may have been the reason in the questioner's case. Take a look at its man page.

Answer 17

If you want to do it in your script, put this in there:

parent=$$
( sleep 5 && kill -HUP $parent ) 2>/dev/null &

Answer 18

#! /bin/bash
timeout=10
interval=1
delay=3
(
    ((t = timeout)) || :

    while ((t > 0)); do
        echo "$t"
        sleep $interval
        # Check if the process still exists.
        kill -0 $$ 2> /dev/null || exit 0
        ((t -= interval)) || :
    done

    # Be nice, post SIGTERM first.
    { echo SIGTERM to $$ ; kill -s TERM $$ ; sleep $delay ; kill -0 $$ 2> /dev/null && { echo SIGKILL to $$ ; kill -s KILL $$ ; } ; }
) &

exec "$@"

Answer 19

I was presented with a problem to preserve the shell context and allow timeouts, the only problem with it is it will stop script execution on the timeout - but it's fine with the needs I was presented:

#!/usr/bin/env bash

safe_kill()
{
  ps aux | grep -v grep | grep $1 >/dev/null && kill ${2:-} $1
}

my_timeout()
{
  typeset _my_timeout _waiter_pid _return
  _my_timeout=$1
  echo "Timeout($_my_timeout) running: $*"
  shift
  (
    trap "return 0" USR1
    sleep $_my_timeout
    echo "Timeout($_my_timeout) reached for: $*"
    safe_kill $$
  ) &
  _waiter_pid=$!
  "$@" || _return=$?
  safe_kill $_waiter_pid -USR1
  echo "Timeout($_my_timeout) ran: $*"
  return ${_return:-0}
}

my_timeout 3 cd scripts
my_timeout 3 pwd
my_timeout 3 true  && echo true || echo false
my_timeout 3 false && echo true || echo false
my_timeout 3 sleep 10
my_timeout 3 pwd

with the outputs:

Timeout(3) running: 3 cd scripts
Timeout(3) ran: cd scripts
Timeout(3) running: 3 pwd
/home/mpapis/projects/rvm/rvm/scripts
Timeout(3) ran: pwd
Timeout(3) running: 3 true
Timeout(3) ran: true
true
Timeout(3) running: 3 false
Timeout(3) ran: false
false
Timeout(3) running: 3 sleep 10
Timeout(3) reached for: sleep 10
Terminated

of course I assume there was a dir called scripts

Answer 20

My problem was maybe a bit different : I start a command via ssh on a remote machine and want to kill the shell and childs if the command hangs.

I now use the following :

ssh server '( sleep 60 && kill -9 0 ) 2>/dev/null & my_command; RC=$? ; sleep 1 ; pkill -P $! ; exit $RC'

This way the command returns 255 when there was a timeout or the returncode of the command in case of success

Please note that killing processes from a ssh session is handled different from an interactive shell. But you can also use the -t option to ssh to allocate a pseudo terminal, so it acts like an interactive shell

Answer 21

Building on @loup's answer...

If you want to timeout a process and silence the kill job/pid output, run:

( (sleep 1 && killall program 2>/dev/null) &) && program --version 

This puts the backgrounded process into a subshell so you don't see the job output.

Answer 22

A very simplistic way:

# command & sleep 5; pkill -9 -x -f "command"

with pkill (option -f) you can kill your specific command with arguments or specify -n to avoid kill old process.

Answer 23

In 99% of the cases the answer is NOT to implement any timeout logic. Timeout logic is in nearly any situation a red warning sign that something else is wrong and should be fixed instead.

Is your process hanging or breaking after n seconds sometimes? Then find out why and fix that instead.

As an aside, to do strager's solution right, you need to use wait "$SPID" instead of fg 1, since in scripts you don't have job control (and trying to turn it on is stupid). Moreover, fg 1 relies on the fact that you didn't start any other jobs previously in the script which is a bad assumption to make.

Answer 24

I have a cron job that calls a php script and, some times, it get stuck on php script. This solution was perfect to me.

I use:

scripttimeout -t 60 /script.php