How to kill a child process after a given timeout in Bash

Question

I have a bash script that launches a child process that crashes  actually  hangs  from time to time and with no apparent reason  closed source  so there isn t much I can do about it   As a result  I would like to be able to launch this process for a given amount of time  and kill it if it did not return successfully after a given amount of time   Is there a simple and robust way to achieve that using bash    P S   tell me if this question is better suited to serverfault or superuser

User · Answer

One way is to run the program in a subshell, and communicate with the subshell through a named pipe with the read command. This way you can check the exit status of the process being run and communicate this back through the pipe.

Here's an example of timing out the yes command after 3 seconds. It gets the PID of the process using pgrep (possibly only works on Linux). There is also some problem with using a pipe in that a process opening a pipe for read will hang until it is also opened for write, and vice versa. So to prevent the read command hanging, I've "wedged" open the pipe for read with a background subshell. (Another way to prevent a freeze to open the pipe read-write, i.e. read -t 5 <>finished.pipe - however, that also may not work except with Linux.)

rm -f finished.pipe
mkfifo finished.pipe

{ yes >/dev/null; echo finished >finished.pipe ; } &
SUBSHELL=$!

# Get command PID
while : ; do
    PID=$( pgrep -P $SUBSHELL yes )
    test "$PID" = "" || break
    sleep 1
done

# Open pipe for writing
{ exec 4>finished.pipe ; while : ; do sleep 1000; done } &  

read -t 3 FINISHED <finished.pipe

if [ "$FINISHED" = finished ] ; then
  echo 'Subprocess finished'
else
  echo 'Subprocess timed out'
  kill $PID
fi

rm finished.pipe

User · Answer

Assuming you have  or can easily make  a pid file for tracking the child s pid  you could then create a script that checks the modtime of the pid file and kills respawns the process as needed  Then just put the script in crontab to run at approximately the period you need   Let me know if you need more details  If that doesn t sound like it d suit your needs  what about upstart

User · Answer

sleep 999 amp  t    sleep 10 kill  t

User · Answer

Kill command after 10 seconds timeout 10 command   If you don t have timeout installed  this is almost the same  sh -c   sleep 10  kill  quot    quot    amp  command    The same as above  with muted duplicate messages  sh -c   sleep 10  kill  quot    quot  2 gt  dev null   amp  command

User · Answer

Here s an attempt which tries to avoid killing a process after it has already exited  which reduces the chance of killing another process with the same process ID  although it s probably impossible to avoid this kind of error completely    run with timeout        t  1   shift    echo  running        with timeout  t           first  run process in background    exec sh -c        amp    pid      echo  pid      the timeout shell    sleep  t   echo timeout   amp    waiter      echo  waiter      finally  allow process to end naturally   wait  pid   echo               read pid      read waiter       if test  waiter    timeout   then        read status      else        status timeout      fi         if we timed out  kill the process      if test  status   timeout   then        kill  pid        exit 99      else          if the program exited normally  kill the waiting shell        kill  waiter        exit  status      fi         Use like run with timeout 3 sleep 10000  which runs sleep 10000 but ends it after 3 seconds   This is like other answers which use a background timeout process to kill the child process after a delay  I think this is almost the same as Dan s extended answer  https   stackoverflow com a 5161274 1351983   except the timeout shell will not be killed if it has already ended   After this program has ended  there will still be a few lingering  sleep  processes running  but they should be harmless   This may be a better solution than my other answer because it does not use the non-portable shell feature read -t and does not use pgrep

User · Answer

I also had this question and found two more things very useful    The SECONDS variable in bash  The command  pgrep     So I use something like this on the command line  OSX 10 9    ping www goooooogle com  amp  PING PID   pgrep  ping    SECONDS 0  while pgrep -q  ping   do sleep 0 2  if    SECONDS   10    then kill  PING PID  fi  done   As this is a loop I included a  sleep 0 2  to keep the CPU cool   -    BTW  ping is a bad example anyway  you just would use the built-in  -t   timeout  option

User · Answer

As seen in  BASH FAQ entry  68   How do I run a command  and have it abort  timeout  after N seconds     If you don t mind downloading something  use timeout  sudo apt-get install timeout  and use it like   most Systems have it already installed otherwise use sudo apt-get install coreutils   timeout 10 ping www goooooogle com   If you don t want to download something  do what timeout does internally     cmdpid  BASHPID   sleep 10  kill  cmdpid   amp  exec ping www goooooogle com     In case that you want to do a timeout for longer bash code  use the second option as such     cmdpid  BASHPID        sleep 10  kill  cmdpid        amp  while   ping -w 1 www goooooogle com       do           echo crap        done

User · Answer

Here s the third answer I ve submitted here   This one handles signal interrupts and cleans up background processes when SIGINT is received  It uses the  BASHPID and exec trick used in the top answer to get the PID of a process  in this case    in a sh invocation   It uses a FIFO to communicate with a subshell that is responsible for killing and cleanup    This is like the pipe in my second answer  but having a named pipe means that the signal handler can write into it too    run with timeout        t  1   shift    trap cleanup 2    F    fifo   rm -f  F   mkfifo  F      first  run main process in background         amp  pid         sleeper process to time out     sh -c  echo       gt  F   exec sleep  t    echo timeout  gt  F    amp    read sleeper  lt  F      control shell  read from fifo      final input is  finished    after that     we clean up   we can get a timeout or a     signal first      exec 0 lt  F     while     do       read input       case  input in         finished            test  sleeper    0  amp  amp  kill  sleeper           rm -f  F           exit 0                      timeout            test  pid    0  amp  amp  kill  pid           sleeper 0                      signal            test  pid    0  amp  amp  kill  pid                    esac     done      amp       wait for process to end   wait  pid   status      echo finished  gt  F   return  status    cleanup        echo signal  gt    fifo     I ve tried to avoid race conditions as far as I can  However  one source of error I couldn t remove is when the process ends near the same time as the timeout  For example  run with timeout 2 sleep 2 or run with timeout 0 sleep 0   For me  the latter gives an error   timeout sh  line 250  kill   23248  - No such process   as it is trying to kill a process that has already exited by itself

User · Answer

Spawn a child process   dosmth   amp  pid      in the background  sleep for 10 secs then kill that process  sleep 10  amp  amp  kill -9  pid   amp    or to get the exit codes as well     Spawn a child process   dosmth   amp  pid      in the background  sleep for 10 secs then kill that process  sleep 10  amp  amp  kill -9  pid   amp  waiter      wait on our worker process and return the exitcode exitcode   wait  pid  amp  amp  echo       kill the waiter subshell  if it still runs kill -9  waiter 2 gt  dev null   0 if we killed the waiter  cause that means the process finished before the waiter finished gracefully

[linux] How to kill a child process after a given timeout in Bash?

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