On Tue, 24 Apr 2012, Denys Vlasenko wrote:
On Tue, Apr 24, 2012 at 1:18 PM, Tomasz Czapiewski <[email protected]> wrote:
On Tue, 24 Apr 2012, Denys Vlasenko wrote:
On Tue, Apr 24, 2012 at 11:27 AM, Tomasz Czapiewski <[email protected]> wrote:
dmesg:
Mon Apr 23 23:16:57 2012: process '/sbin/getty -L ttyS0 115200 vt102'
(pid
909) exited. Scheduling for restart.
I'm also getting "getty: setsid: Operation not permitted" when trying to
run
above command from shell.
It means that setsid fails. We used to just assume it always succeeds.
Which was wrong. For one, successful setsid drops ctty,
but failing one does not.
setsid fails if getty is started in a way so that it is a process leader,
but not a session leader. For one, this is what happens
when you run a single command (not a pipe) from interactive shell:
it is made a process leader by the shell. That's why getty
from interactive shell doesn't work (and probably is not expected to).
How do you start your getty? From init? Which init - busybox's?
Yes, it's started from init, which is a symlink to the same busybox binary.
/etc/inittab:
::sysinit:/etc/init.d/rcS
ttyS0::respawn:/sbin/getty -L ttyS0 115200 vt102
::ctrlaltdel:/sbin/reboot
null::shutdown:/bin/umount -a -r
(changing order of ttyS0 and 115200 arguments doesn't seem to make any
difference)
This is strange. bbox init always puts its children in their own
sessions (meaning it makes them session leaders). See run()
function in init.c: it does setsid() in the child, immediately
after [v]fork.
Let's verify that.
Can you add a debugging printout in getty_main() here?
/* Create new session and pgrp, lose controlling tty */
bb_error_msg("pid:%d", getpid());
bb_error_msg("sid:%d", getsid(0));
pid = setsid(); /* this also gives us our pid :) */
if (pid < 0) {
...
run it and tell me what do you observe?
--
vda
starting pid 1, tty '/dev/ttyS0': '/sbin/getty -L ttyS0 115200 vt102'
getty: pid:1078
getty: sid:1078
process '/sbin/getty -L ttyS0 115200 vt102' (pid 1078) exited.
Scheduling for restart.
starting pid 1, tty '/dev/ttyS0': '/sbin/getty -L ttyS0 115200 vt102'
getty: pid:1079
getty: sid:1079
process '/sbin/getty -L ttyS0 115200 vt102' (pid 1079) exited.
Scheduling for restart.
starting pid 1, tty '/dev/ttyS0': '/sbin/getty -L ttyS0 115200 vt102'
getty: pid:1080
getty: sid:1080
process '/sbin/getty -L ttyS0 115200 vt102' (pid 1080) exited.
Scheduling for restart.
starting pid 1, tty '/dev/ttyS0': '/sbin/getty -L ttyS0 115200 vt102'
getty: pid:1081
getty: sid:1081
...
Besides those, init logs this at start:
init started: BusyBox v1.20.0 (2012-04-24 21:11:59 CEST)
starting pid 1, tty '': '/etc/init.d/rcS'
--
Tom
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