How to properly sigint a bash script that is run from another bash script?

Question

I have two scripts, in which one is calling the other, and needs to kill it after some time. A very basic, working example is given below.

main_script.sh:

#!/bin/bash
cd "${0%/*}" #make current working directory the folder of this script
./record.sh &
PID=$!
# perform some other commands
sleep 5
kill -s SIGINT $PID
#wait $PID
echo "Finished"

record.sh:

#!/bin/bash
cd "${0%/*}" #make current working directory the folder of this script
RECORD_PIDS=1
printf "WallTimeStart: %f\n\n" $(date +%s.%N) >> test.txt
top -b -p $RECORD_PIDS -d 1.00 >> test.txt
printf "WallTimeEnd: %f\n\n" $(date +%s.%N) >> test.txt

Now, if I run main_script.sh, it will not nicely close record.sh on finish: the top command will keep on running in the background (test.txt will grow until you manually kill the top process), even though the main_script is finished and the record script is killed using SIGINT.

If I ctrl+c the main_script.sh, everything shuts down properly. If I run record.sh on its own and ctrl+c it, everything shuts down properly as well.

If I uncomment wait, the script will hang and I will need to ctrl+z it.

I have already tried all kinds of things, including using 'trap' to launch some cleanup script when receiving a SIGINT, EXIT, and/or SIGTERM, but nothing worked. I also tried bring record.sh back to the foreground using fg, but that did not help too. I have been searching for nearly a day now already, with now luck unfortunately. I have made an ugly workaround which uses pidof to find the top process and kill it manually (from main_script.sh), and then I have to write the "WallTimeEnd" statement manually to it as well from the main_script.sh. Not very satisfactory to me...

Looking forward to any tips!

Cheers, Koen

score 4 · Accepted Answer · answered Aug 27 '14 at 15:59

Your issue is that the SIGINT is delivered to bash rather than to top. One option would be to use a new session and send the signal to the process group instead, like:

#!/bin/bash
cd "${0%/*}" #make current working directory the folder of this script
setsid ./record.sh &
PID=$!
# perform some other commands
sleep 5
kill -s SIGINT -$PID
wait $PID
echo "Finished"

This starts the sub-script in a new process group and the -pid tells kill to signal every process in that group, which will include top.

How to properly sigint a bash script that is run from another bash script?

1 Answers1