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Re: Possible bash bug?


From: Reuti
Subject: Re: Possible bash bug?
Date: Wed, 22 Jun 2016 15:48:01 +0200

> Am 22.06.2016 um 11:34 schrieb John Lawlor <address@hidden>:
> 
> Hi,
>  
> I came across some unusual behaviour in bash using the ā€˜-cā€™ 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

This kills just the specified process.

What does happen when you issue:

$ kill %1

(resp. the the number output when issuing the above command) instead?

-- Reuti


>  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 ā€“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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