How do I kill background processes jobs when my shell script exits

Question

I am looking for a way to clean up the mess when my top-level script exits   Especially if I want to use set -e  I wish the background process would die when the script exits

User · Answer

Another option is it to have the script set itself as the process group leader  and trap a killpg on your process group on exit

User · Answer

I made an adaption of  tokland s answer combined with the knowledge from http   veithen github io 2014 11 16 sigterm-propagation html when I noticed that trap doesn t trigger if I m running a foreground process  not backgrounded with  amp        bin bash    killable-shell sh  Kills itself and all children  the whole process group  when killed    Adapted from http   stackoverflow com a 2173421 and http   veithen github io 2014 11 16 sigterm-propagation html   Note  Does not work  and cannot work  when the shell itself is killed with SIGKILL  for then the trap is not triggered  trap  trap - SIGTERM  amp  amp  echo  Caught SIGTERM  sending SIGTERM to process group   amp  amp  kill -- -    SIGINT SIGTERM EXIT  echo          amp  PID    wait  PID trap - SIGINT SIGTERM EXIT wait  PID   Example of it working     bash killable-shell sh sleep 100 sleep 100  Z  1     31568 suspended  bash killable-shell sh sleep 100    ps aux   grep  sleep  niklas   31568  0 0  0 0  19640  1440 pts 18   T    01 30   0 00 bash killable-shell sh sleep 100 niklas   31569  0 0  0 0  14404   616 pts 18   T    01 30   0 00 sleep 100 niklas   31605  0 0  0 0  18956   936 pts 18   S    01 30   0 00 grep --color auto sleep    bg  1     31568 continued  bash killable-shell sh sleep 100    kill 31568 Caught SIGTERM  sending SIGTERM to process group  1     31568 terminated  bash killable-shell sh sleep 100    ps aux   grep  sleep  niklas   31717  0 0  0 0  18956   936 pts 18   S    01 31   0 00 grep --color auto sleep

User · Answer

To clean up some mess  trap can be used  It can provide a list of stuff executed when a specific signal arrives   trap  echo hello  SIGINT   but can also be used to execute something if the shell exits   trap  killall background  EXIT   It s a builtin  so help trap will give you information  works with bash   If you only want to kill background jobs  you can do  trap  kill   jobs -p   EXIT   Watch out to use single    to prevent the shell from substituting the     immediately

User · Answer

To be on the safe side I find it better to define a cleanup function and call it from trap   cleanup             local pids   jobs -pr            -n   pids     amp  amp  kill  pids   trap  cleanup  INT QUIT TERM EXIT         or avoiding the function altogether   trap    -n    jobs -pr      amp  amp  kill   jobs -pr   INT QUIT TERM EXIT         Why  Because by simply using trap  kill   jobs -pr         one assumes that there will be background jobs running when the trap condition is signalled  When there are no jobs one will see the following  or similar  message   kill  usage  kill  -s sigspec   -n signum   -sigspec  pid   jobspec     or kill -l  sigspec    because jobs -pr is empty - I ended in that  trap   pun intended

User · Answer

So script the loading of the script  Run a killall  or whatever is available on your OS  command that executes as soon as the script is finished

User · Answer

To be on the safe side I find it better to define a cleanup function and call it from trap   cleanup             local pids   jobs -pr            -n   pids     amp  amp  kill  pids   trap  cleanup  INT QUIT TERM EXIT         or avoiding the function altogether   trap    -n    jobs -pr      amp  amp  kill   jobs -pr   INT QUIT TERM EXIT         Why  Because by simply using trap  kill   jobs -pr         one assumes that there will be background jobs running when the trap condition is signalled  When there are no jobs one will see the following  or similar  message   kill  usage  kill  -s sigspec   -n signum   -sigspec  pid   jobspec     or kill -l  sigspec    because jobs -pr is empty - I ended in that  trap   pun intended

User · Answer

trap  kill   jobs -p   EXIT   I would make only minor changes to Johannes  answer and use jobs -pr to limit the kill to running processes and add a few more signals to the list   trap  kill   jobs -pr   SIGINT SIGTERM EXIT

User · Answer

So script the loading of the script  Run a killall  or whatever is available on your OS  command that executes as soon as the script is finished

User · Answer

Update  https   stackoverflow com a 53714583 302079 improves this by adding exit status and a cleanup function   trap  exit  INT TERM trap  kill 0  EXIT   Why convert INT and TERM to exit  Because both should trigger the kill 0 without entering an infinite loop    Why trigger kill 0 on EXIT  Because normal script exits should trigger kill 0  too    Why kill 0  Because nested subshells need to be killed as well  This will take down the whole process tree

User · Answer

The trap  kill 0  SIGINT SIGTERM EXIT solution described in  tokland s answer is really nice  but latest Bash crashes with a segmentation fault when using it  That s because Bash  starting from v   4 3  allows trap recursion  which becomes infinite in this case   shell process receives SIGINT or SIGTERM or EXIT  the signal gets trapped  executing kill 0  which sends SIGTERM to all processes in the group  including the shell itself  go to 1     This can be worked around by manually de-registering the trap   trap  trap - SIGTERM  amp  amp  kill 0  SIGINT SIGTERM EXIT  The more fancy way that allows printing the received signal and avoids  quot Terminated  quot  messages     usr bin env bash  trap with arg       from https   stackoverflow com a 2183063 804678   local func  quot  1 quot   shift   for sig in  quot    quot   do     trap  quot  func  sig quot   quot  sig quot    done    stop       trap - SIGINT EXIT   printf   n s n   quot received  1  killing child processes quot    kill -s SIGINT 0    trap with arg  stop  EXIT SIGINT SIGTERM SIGHUP    i 0  while      i     do sleep 0 5  amp  amp  echo  quot a   i quot   done    amp    i 0  while      i     do sleep 0 6  amp  amp  echo  quot b   i quot   done    amp   while true  do read  done  UPD  added a minimal example  improved stop function to avoid de-trapping unnecessary signals and to hide  quot Terminated  quot  messages from the output  Thanks Trevor Boyd Smith for the suggestions

User · Answer

To clean up some mess  trap can be used  It can provide a list of stuff executed when a specific signal arrives   trap  echo hello  SIGINT   but can also be used to execute something if the shell exits   trap  killall background  EXIT   It s a builtin  so help trap will give you information  works with bash   If you only want to kill background jobs  you can do  trap  kill   jobs -p   EXIT   Watch out to use single    to prevent the shell from substituting the     immediately

User · Answer

This works for me  improved thanks to the commenters    trap  trap - SIGTERM  amp  amp  kill -- -    SIGINT SIGTERM EXIT    kill -- -   sends a SIGTERM to the whole process group  thus killing also descendants  Specifying signal EXIT is useful when using set -e  more details here

User · Answer

A nice version that works under Linux  BSD and MacOS X  First tries to send SIGTERM  and if it doesn t succeed  kills the process after 10 seconds   KillJobs         for job in   jobs -p   do             kill -s SIGTERM  job  gt   dev null 2 gt  amp 1     sleep 10  amp  amp  kill -9  job  gt   dev null 2 gt  amp 1  amp        done    TrapQuit           Whatever you need to clean here     KillJobs    trap TrapQuit EXIT   Please note that jobs does not include grand children processes

User · Answer

trap  kill   jobs -p   EXIT   I would make only minor changes to Johannes  answer and use jobs -pr to limit the kill to running processes and add a few more signals to the list   trap  kill   jobs -pr   SIGINT SIGTERM EXIT

User · Answer

Another option is it to have the script set itself as the process group leader  and trap a killpg on your process group on exit

User · Answer

So script the loading of the script  Run a killall  or whatever is available on your OS  command that executes as soon as the script is finished

User · Answer

I made an adaption of  tokland s answer combined with the knowledge from http   veithen github io 2014 11 16 sigterm-propagation html when I noticed that trap doesn t trigger if I m running a foreground process  not backgrounded with  amp        bin bash    killable-shell sh  Kills itself and all children  the whole process group  when killed    Adapted from http   stackoverflow com a 2173421 and http   veithen github io 2014 11 16 sigterm-propagation html   Note  Does not work  and cannot work  when the shell itself is killed with SIGKILL  for then the trap is not triggered  trap  trap - SIGTERM  amp  amp  echo  Caught SIGTERM  sending SIGTERM to process group   amp  amp  kill -- -    SIGINT SIGTERM EXIT  echo          amp  PID    wait  PID trap - SIGINT SIGTERM EXIT wait  PID   Example of it working     bash killable-shell sh sleep 100 sleep 100  Z  1     31568 suspended  bash killable-shell sh sleep 100    ps aux   grep  sleep  niklas   31568  0 0  0 0  19640  1440 pts 18   T    01 30   0 00 bash killable-shell sh sleep 100 niklas   31569  0 0  0 0  14404   616 pts 18   T    01 30   0 00 sleep 100 niklas   31605  0 0  0 0  18956   936 pts 18   S    01 30   0 00 grep --color auto sleep    bg  1     31568 continued  bash killable-shell sh sleep 100    kill 31568 Caught SIGTERM  sending SIGTERM to process group  1     31568 terminated  bash killable-shell sh sleep 100    ps aux   grep  sleep  niklas   31717  0 0  0 0  18956   936 pts 18   S    01 31   0 00 grep --color auto sleep

User · Answer

To clean up some mess  trap can be used  It can provide a list of stuff executed when a specific signal arrives   trap  echo hello  SIGINT   but can also be used to execute something if the shell exits   trap  killall background  EXIT   It s a builtin  so help trap will give you information  works with bash   If you only want to kill background jobs  you can do  trap  kill   jobs -p   EXIT   Watch out to use single    to prevent the shell from substituting the     immediately

User · Answer

The trap  kill 0  SIGINT SIGTERM EXIT solution described in  tokland s answer is really nice  but latest Bash crashes with a segmentation fault when using it  That s because Bash  starting from v   4 3  allows trap recursion  which becomes infinite in this case   shell process receives SIGINT or SIGTERM or EXIT  the signal gets trapped  executing kill 0  which sends SIGTERM to all processes in the group  including the shell itself  go to 1     This can be worked around by manually de-registering the trap   trap  trap - SIGTERM  amp  amp  kill 0  SIGINT SIGTERM EXIT  The more fancy way that allows printing the received signal and avoids  quot Terminated  quot  messages     usr bin env bash  trap with arg       from https   stackoverflow com a 2183063 804678   local func  quot  1 quot   shift   for sig in  quot    quot   do     trap  quot  func  sig quot   quot  sig quot    done    stop       trap - SIGINT EXIT   printf   n s n   quot received  1  killing child processes quot    kill -s SIGINT 0    trap with arg  stop  EXIT SIGINT SIGTERM SIGHUP    i 0  while      i     do sleep 0 5  amp  amp  echo  quot a   i quot   done    amp    i 0  while      i     do sleep 0 6  amp  amp  echo  quot b   i quot   done    amp   while true  do read  done  UPD  added a minimal example  improved stop function to avoid de-trapping unnecessary signals and to hide  quot Terminated  quot  messages from the output  Thanks Trevor Boyd Smith for the suggestions

User · Answer

Another option is it to have the script set itself as the process group leader  and trap a killpg on your process group on exit

User · Answer

Just for diversity I will post variation of https   stackoverflow com a 2173421 102484   because that solution leads to message  Terminated  in my environment   trap  test -z   intrap   amp  amp  export intrap 1  amp  amp  kill -- -    SIGINT SIGTERM EXIT

User · Answer

So script the loading of the script  Run a killall  or whatever is available on your OS  command that executes as soon as the script is finished

User · Answer

Update  https   stackoverflow com a 53714583 302079 improves this by adding exit status and a cleanup function   trap  exit  INT TERM trap  kill 0  EXIT   Why convert INT and TERM to exit  Because both should trigger the kill 0 without entering an infinite loop    Why trigger kill 0 on EXIT  Because normal script exits should trigger kill 0  too    Why kill 0  Because nested subshells need to be killed as well  This will take down the whole process tree

User · Answer

Another option is it to have the script set itself as the process group leader  and trap a killpg on your process group on exit

User · Answer

This works for me  improved thanks to the commenters    trap  trap - SIGTERM  amp  amp  kill -- -    SIGINT SIGTERM EXIT    kill -- -   sends a SIGTERM to the whole process group  thus killing also descendants  Specifying signal EXIT is useful when using set -e  more details here

User · Answer

A nice version that works under Linux  BSD and MacOS X  First tries to send SIGTERM  and if it doesn t succeed  kills the process after 10 seconds   KillJobs         for job in   jobs -p   do             kill -s SIGTERM  job  gt   dev null 2 gt  amp 1     sleep 10  amp  amp  kill -9  job  gt   dev null 2 gt  amp 1  amp        done    TrapQuit           Whatever you need to clean here     KillJobs    trap TrapQuit EXIT   Please note that jobs does not include grand children processes

User · Answer

function cleanup func       sleep 0 5     echo cleanup    trap  exit   exit code  INT TERM trap  exit code      cleanup func  kill 0  EXIT    exit 1   exit 0   Like https   stackoverflow com a 22644006 10082476  but with added exit-code

User · Answer

Just for diversity I will post variation of https   stackoverflow com a 2173421 102484   because that solution leads to message  Terminated  in my environment   trap  test -z   intrap   amp  amp  export intrap 1  amp  amp  kill -- -    SIGINT SIGTERM EXIT

User · Answer

jobs -p does not work in all shells if called in a sub-shell  possibly unless its output is redirected into a file but not a pipe    I assume it was originally intended for interactive use only    What about the following   trap  while kill    2 gt  dev null  do jobs  gt   dev null  done  INT TERM EXIT         The call to  jobs  is needed with Debian s dash shell  which fails to update the current job        if it is missing

User · Answer

To clean up some mess  trap can be used  It can provide a list of stuff executed when a specific signal arrives   trap  echo hello  SIGINT   but can also be used to execute something if the shell exits   trap  killall background  EXIT   It s a builtin  so help trap will give you information  works with bash   If you only want to kill background jobs  you can do  trap  kill   jobs -p   EXIT   Watch out to use single    to prevent the shell from substituting the     immediately

User · Answer

function cleanup func       sleep 0 5     echo cleanup    trap  exit   exit code  INT TERM trap  exit code      cleanup func  kill 0  EXIT    exit 1   exit 0   Like https   stackoverflow com a 22644006 10082476  but with added exit-code

User · Answer

jobs -p does not work in all shells if called in a sub-shell  possibly unless its output is redirected into a file but not a pipe    I assume it was originally intended for interactive use only    What about the following   trap  while kill    2 gt  dev null  do jobs  gt   dev null  done  INT TERM EXIT         The call to  jobs  is needed with Debian s dash shell  which fails to update the current job        if it is missing

[shell] How do I kill background processes / jobs when my shell script exits?

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