bash script to kill a python script after starting another same python script

Question

I start a python script and then after some time i want to kill it. but before killing it I want to start another copy of this same script and then kill the previous one after starting new one. I want to do this in loop.

here is my code , i just need a clean way to kill scripts.I do not want to use timeouts.

#!/bin/bash 
while true
do
    echo "starting FIRST Consumer.py : $(date +"%T")"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &

    sleep 20
    echo "starting SECOND Consumer.py : $(date +"%T")"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    # Here I want to kill FIRST Consumer.py
    sleep 20
    # Here I want to kill SECOND Consumer.py

done

Any reason you don't want to use timeout 20 python3 ... ? man7.org/linux/man-pages/man1/timeout.1.html — Olf
– Olf, Commented Jan 29, 2019 at 13:19
yes i was using timeouts but sometimes it doesnt kill my scripts. but starts new ones. after some time i had 8 scripts running. — irum zahra
– irum zahra, Commented Jan 29, 2019 at 13:21
Are you sure about the comments in your code sample? (did you invert SECOND and FIRST ?) — Olf
– Olf, Commented Jan 29, 2019 at 13:24
Clean and kill are kind of conflicting requirements. Where kill means "stop at any cost", and clean meaning "exit gracefully" . If you're program isn't exiting after a SIGTERM signal then it is misbehaving. Fix your python script before resorting to using SIGKILL. Downsides to using SIGKILL include losing state if the process isn't able to save state about what has been consumed. — Dunes
– Dunes, Commented Jan 29, 2019 at 13:45

Poshi · Accepted Answer · 2019-01-29 13:36:48Z

2

You can get the PID of the first process to kill it afterwards:

#!/bin/bash 

while true
do
    echo "starting FIRST Consumer.py : $(date +"%T")"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    pid=$!
    sleep 20

    echo "starting SECOND Consumer.py : $(date +"%T")"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    new_pid=$!

    # Here I want to kill FIRST Consumer.py
    kill "$pid"
    sleep 20

    # Here I want to kill SECOND Consumer.py
    kill "$new_pid"
done

answered Jan 29, 2019 at 13:36

Poshi

5,8533 gold badges22 silver badges37 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

irum zahra Over a year ago

this answer worked for me but when i added -9 to kill command kill -9 "$pid"

Poshi Over a year ago

This detail depends on what are you trying to kill. By default, kill sends a SIGTERM signal (15), and this signal can be catched and processed. It is supposed to give the application a chance to write down it's status and exit grecefully. But if it does not exit, you can always use the SIGKILL (9), which cannot be trapped and forces the system to kill the application.

Socowi · Accepted Answer · 2019-01-29 13:45:14Z

In bash there are two special background jobs: + and -. You can see them in the output of the jobs command:

$ sleep 10 &
$ sleep 20 &
$ sleep 30 &
$ jobs
[1]   Running                 sleep 10 &
[2]-  Running                 sleep 20 &
[3]+  Running                 sleep 30 &

+ is the most recent running job. - is the most recent job before +. Both will update if you kill a job or start a new one. Therefore you could complete your script as follows:

#!/bin/bash 
while true; do
    echo "starting FIRST Consumer.py : $(date +%T)"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    sleep 20
    echo "starting SECOND Consumer.py : $(date +%T)"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    kill %- # kill FIRST Consumer.py
    sleep 20
    kill %+ # kill SECOND Consumer.py
done

This only works reliably if Consumer.py always runs longer than 20 seconds. If Consumer.py could terminate before the 20 second are over, then we may kill the wrong job. To work around this issue, you can use (python3 .../Consumer.py; sleep inf) & instead of python3 .../Consumer.py &. The sleep inf will stop the job from terminating on its own.

Jay jargot · Accepted Answer · 2019-01-30 08:20:07Z

2

Each time a background process is started, bash maintains a jobs list, with ids starting from 1.

The jobs builtin lists the background jobs.

in you situation, you would add the kill %1 to kill the first background job ever started, and then kill %2

== EDITED == Your script becomes:

#!/bin/bash 
while : ; do
   echo "starting FIRST Consumer.py : $(date +"%T")"
   python3 /home/irum/Desktop/Marketsyc/Consumer.py &

   sleep 20
   echo "starting SECOND Consumer.py : $(date +"%T")"
   python3 /home/irum/Desktop/Marketsyc/Consumer.py &

   kill %1

   sleep 20

   kill %2

   wait
 done

edited Jan 30, 2019 at 8:20

answered Jan 29, 2019 at 13:34

Jay jargot

2,8881 gold badge13 silver badges16 bronze badges

9 Comments

Socowi Over a year ago

The job ids always increase. %1 and %2 are only correct for the first iteration. In the second iteration you would have to use %3 and %4. You can access the PID (not job id) of the last job with $!.

Jay jargot Over a year ago

@Socowi: as the loop is ending without any background jobs, the ids are always 1 and 2. This is confirmed with my tests.

Socowi Over a year ago

Are you sure? I tested my claim in bash 4.4.19(1) and 5.0.0(1) on two different systems. For me, the following script quickly prints numbers > 2. while :; do sleep 10 & sleep 20 & kill %1; kill %2; jobs | wc -l; done.

Socowi Over a year ago

Maybe you are right nevertheless. sleep 1 & kill %1; sleep 2 & jobs creates the job ids %1 and %2, but sleep 1 & kill %1; sleep 0.5; sleep 2 & jobs uses the job id %1 twice. Seems like kill is asynchronous and we need a small pause between killing an old job and starting a new one such that the old job id is freed before the new job is started.

Poshi Over a year ago

This small quirks are the reason I prefer to work with PIDs in scripts. Interactive job management is another beast.

|

Gioachino Bartolotta · Accepted Answer · 2019-01-30 13:26:20Z

0

I would do this

    #!/bin/bash 
function check_pid() {
    if /bin/ps -p $1 > /dev/null
    then
        kill $1
    else
        echo "not running"
    fi
}

while true
do
    echo "starting FIRST Consumer.py : $(date +"%T")"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    pid1=$!
    sleep 20
    echo "starting SECOND Consumer.py : $(date +"%T")"
    python3 /home/irum/Desktop/Marketsyc/Consumer.py &
    pid2=$!
    # Here I want to kill FIRST Consumer.py
    check_pid $pid1
    sleep 20
    # Here I want to kill SECOND Consumer.py
    check_pid $pid2
done

In this way, the process will be killed only if it is still running.

answered Jan 30, 2019 at 13:26

Gioachino Bartolotta

1231 silver badge10 bronze badges

Collectives™ on Stack Overflow

bash script to kill a python script after starting another same python script

4 Answers 4

2 Comments

Comments

9 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

9 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related