Re: zsh mysteriously suspending job with sudo

[Ronan Pigott <rpigott314@gmail.com>]

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Brilliant! Thank you Peter for the patch.

I have applied it to my zsh and pacman is working again.

On Sun, Feb 23, 2020 at 11:53 AM Ronan Pigott <rpigott314@gmail.com> wrote:

> Wow! Thank you Stephane for your analysis.
>
> So you think that a patch checking for ESRCH is not suitable?
>
> I tried poking around in Src/jobs.c in update_job where
> it sounds like this issue originates, but I'm not quite sure
> how the logic should be revised.
>
> Is there somewhere else where this bug should be reported?
>
> Thanks again for your help!
>
>
> On Sun, Feb 23, 2020 at 7:03 AM Stephane Chazelas <stephane@chazelas.org>
> wrote:
>
>> 2020-02-22 18:09:13 -0700, Ronan Pigott:
>> [...]
>> > $ sudo true
>> > [sudo] password for ronan:
>> > $ pacman -Qttdq | sudo pacman -Rns -
>> > [...]
>> > :: Do you want to remove these packages? [Y/n] zsh: done
>> >  pacman -Qttdq |
>> > zsh: suspended (tty output)  sudo pacman -Rns -
>> [...]
>>
>> Can be reproduced with:
>>
>> $ sleep 1 | sudo sh -c 'sleep 2; ps -jfHt "$(tty<&2)"; awk "{print \$8}"
>> /proc/self/stat /dev/tty'
>> UID        PID  PPID  PGID   SID  C STIME TTY          TIME CMD
>> chazelas 25430  8308 25430 25430  0 13:44 pts/1    00:00:00 /bin/zsh
>> root     26867 25430 26866 25430  0 13:46 pts/1    00:00:00   sudo sh -c
>> sleep 2; ps -jfHt "$(tty<&2)"; awk "{print \$8}" /proc/self/stat /dev/tty
>> root     26868 26867 26866 25430  0 13:46 pts/1    00:00:00     sh -c
>> sleep 2; ps -jfHt "$(tty<&2)"; awk "{print \$8}" /proc/self/stat /dev/tty
>> root     26871 26868 26866 25430  0 13:46 pts/1    00:00:00       ps
>> -jfHt /dev/pts/1
>> 25430
>> zsh: done                   sleep 1 |
>> zsh: suspended (tty input)  sudo sh -c
>>
>> As seen above, at the time "ps" is run (and awk later), the
>> foreground process group of the terminal is 25430 which is the
>> pgid of the main shell, not the pgid of the foreground job
>> (26866), which is why that job gets a SIGTTIN when awk tries to
>> read from the terminal (or SIGTTOU when pacman does an ioctl to
>> the terminal).
>>
>> From "strace", it seems it's because when "sleep 1" (the process
>> group leader) finishes, zsh does a kill(-26866,0), presumably to
>> check that the process group is still alive, but that fails with
>> EPERM as there are processes running as root in that group, and
>> then zsh changes the foreground process group back to the main
>> shell's.
>>
>> So it seems indeed to be a bug in zsh.
>>
>> I suppose an easy fix would be to check for an errno of ESRCH
>> when kill(-pgid,0) fails to make sure it's because the process
>> group is gone. But, here the shell should be able to know that
>> the job is not gone as sudo, a direct children of the shell has
>> not returned yet, so there's probably something wrong with the
>> logic in the first place.
>>
>> --
>> Stephane
>>
>