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Possible bash bug?


From: John Lawlor
Subject: Possible bash bug?
Date: Wed, 22 Jun 2016 10:34:59 +0100

Hi,

 

I came across some unusual behaviour in bash using the ‘-c’ parameter.

 

If I do the following:

 

bash -c "ping 127.0.0.1 > $HOME/console.log"  &

 

This starts two processes bash and ping:

 

john     18038 17951  0 09:26 pts/14   00:00:00 bash -c ping 127.0.0.1 > /home/john/console.log

john     18039 18038  0 09:26 pts/14   00:00:00 ping 127.0.0.1

 

From the process hierarchy bash is the parent process of ping.

 

Now if I kill bash:

 

kill -15 18038

 

And check the process tree again:

 

UID        PID  PPID  C STIME TTY          TIME CMD

john     17951 30467  0 09:25 pts/14   00:00:00 /bin/bash

john     18039     1  0 09:26 pts/14   00:00:00 ping 127.0.0.1

john     18064 17951  0 09:30 pts/14   00:00:00 ps -f

[1]+  Terminated              bash -c "ping 127.0.0.1 > $HOME/console.log"

 

Bash is killed but not the child ping process. I was expecting that to be killed also.

 

If I repeat the exact same steps with ksh –c, it does kill the ping process.

 

It looks like bash does a double fork or something whereas ksh does only an execute without fork.

 

Regards,

John



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