On Mar 5, 2016 at 00:50 Ángel González wrote:
I was thinking about this and the problem is actually that runuser
returns (and control is returned to the privileged parent) while there's
an unprivileged descendant with a handle to the tty.
Thus, it seems that it could be solved by having runuser run the child
into a new cgroup and refusing to return while there's any remaining
process there.
In general, it is a good idea.
But from compatibility aspect, it is a bad idea to change it to the
default behavior. Imagine all those poorly written legacy helpers that
run daemons without proper disconnecting from the terminal. All those
will be stalled.
I can imagine new --term-wait option, eventually --term-kill. But I am
not sure, whether it is no over-complicated.
Although depending on the exact way that people is expecting to use job
control, that might still interefere despite not changing the session
leader. Do we know actual usages that should continue working?
There is not exact list what will will break.
But imagine that many users use daily things like simple example below.
(In a real life, you will not want to run sleep, but something more
sophisticated (e. g. build process inside chroot that needs sudo).)
# sudo -u nobody sleep 10 &
[1] 28327
~ # fg
sudo -u nobody sleep 10
^Z
[1]+ Stopped sudo -u nobody sleep 10
~ # bg
[1]+ sudo -u nobody sleep 10 &
~ #
~ #
[1]+ Done sudo -u nobody sleep 10
~ #
It will be not possible any more with setsid().
You will get:
# sudo -u nobody sleep 10 &
[1] 28390
~ # fg
sudo -u nobody sleep 10
^Z^Z^Z^Z^Z^Z^Z^Z
You are stuck, ^Z does not work, and you cannot switch the task back to
background. You can only press ^C.
Exactly the same will affect
runuser --command "sleep 10"
Additionally, both su and runuser already offer two variants. You can
test the difference yourself:
Without job control:
su nobody --command "sleep 10" &
vs.
With job control:
su nobody --session-command "sleep 10" &
After calling it, type:
fg
and then Control-Z.
--
Best Regards / S pozdravem,
Stanislav Brabec
software developer
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