Alarm clock: How To Set Timeout For A Shell Command

Q. How can I run a command called foo, and have it timeout / abort after 10 seconds under GNU/Linux running bash shell or script? How do I run command under an alarm clock?

A. You should able to use python / ruby / php or perl to set such timer. Shell do not have in built facility for timeout a command.

Perl program

Here is sample perl code:

perl -e 'alarm shift @ARGV; exec @ARGV' 5 foo arg1 arg2

You may define it as shell function:

alarm() { perl -e 'alarm shift; exec @ARGV' "$@"; }

And call it as follows (wait 20 seconds before alrming foo command:)

alarm 20 foo arg1

Sample shell script

You can use following shell script to set timeout for a command:

:
##########################################################################
# Shellscript:	timeout - set timeout for a command
# Author     :	Heiner Steven <heiner.steven@odn.de>
# Date       :	29.07.1999
# Category   :	File Utilities
# Requires   :
# SCCS-Id.   :	@(#) timeout	1.3 03/03/18
##########################################################################
# Description
#    o	Runs a command, and terminates it (by sending a signal) after
#	a specified time period
#    o	This command first starts itself as a "watchdog" process in the
#	background, and then runs the specified command.
#	If the command did not terminate after the specified
#	number of seconds, the "watchdog" process will terminate
#	the command by sending a signal.
#
# Notes
#    o	Uses the internal command line argument "-p" to specify the
#	PID of the process to terminate after the timeout to the
#	"watchdog" process.
#    o	The "watchdog" process is invoked by the name "$0", so
#	"$0" must be a valid path to the script.
#    o	If this script runs in the environment of the login shell
#	(i.e. it was invoked using ". timeout command...") it will
#	terminate the login session.
##########################################################################
 
PN=`basename "$0"`			# Program name
VER='1.3'
 
TIMEOUT=5				# Default [seconds]
 
Usage () {
    echo >&2 "$PN - set timeout for a command, $VER
usage: $PN [-t timeout] command [argument ...]
     -t: timeout (in seconds, default is $TIMEOUT)"
    exit 1
}
 
Msg () {
    for MsgLine
    do echo "$PN: $MsgLine" >&2
    done
}
 
Fatal () { Msg "$@"; exit 1; }
 
while [ $# -gt 0 ]
do
    case "$1" in
	-p)	ParentPID=$2; shift;;	# Used internally!
	-t)	Timeout="$2"; shift;;
	--)	shift; break;;
	-h)	Usage;;
	-*)	Usage;;
	*)	break;;			# First file name
    esac
    shift
done
 
: ${Timeout:=$TIMEOUT}			# Set default [seconds]
 
if [ -z "$ParentPID" ]
then
    # This is the first invokation of this script.
    # Start "watchdog" process, and then run the command.
    [ $# -lt 1 ] && Fatal "please specify a command to execute"
    "$0" -p $$ -t $Timeout &		# Start watchdog
    #echo >&2 "DEBUG: process id is $$"
    exec "$@"				# Run command
    exit 2				# NOT REACHED
else
    # We run in "watchdog" mode, $ParentPID contains the PID
    # of the process we should terminate after $Timeout seconds.
    [ $# -ne 0 ] && Fatal "please do not use -p option interactively"
 
    #echo >&2 "DEBUG: $$: parent PID to terminate is $ParentPID"
 
    exec >/dev/null 0<&1 2>&1	# Suppress error messages
    sleep $Timeout
    kill $ParentPID &&			# Give process time to terminate
    	(sleep 2; kill -1 $ParentPID) &&
	(sleep 2; kill -9 $ParentPID)
    exit 0
fi

(Credit: Heiner Steven)

doalarm c program

Download doalarm program:
$ wget http://pilcrow.madison.wi.us/sw/doalarm-0.1.7.tgz
Untar program:
$ tar -zxvf doalarm-0.1.7.tg
Compile doalarm:
$ cd doalarm-0.1.7
$ make
$ ./doalarm
Sample output:

Error: missing required parameter
Usage: doalarm [-hr] [-t type] sec command [arg...]
Run command under an alarm clock.

Options:
 -t          Type of timer: 'real' (SIGALRM), 'virtual' (SIGVTALRM),
    --timer= 'profile' (SIGPROF), 'cpu' (SIGXCPU).  Default 'real'.
 -r --recur        Recurring alarm, every sec seconds.
 -h --help         Show help text (this message).
    --version      Display version.

doalarm 0.1.7 (14 Dec 2001)

Run foo as follows:
$ doalarm 20 foo

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