Bash reports error "-bash: child setpgid (12743 to 12739): Operation not permitted" when pipe is used in commands.
 SOLUTION VERIFIED - Updated August 27 2013 at 7:22 AM - English
Environment

Red Hat Enterprise Linux (RHEL) 5
bash-3.2-32.el5
Issue

When pipe character is used in between the commands, bash reports the errors/warnings like follows.
Raw
[root@localhost ~]# ls | less
-bash: child setpgid (12743 to 12739): Operation not permitted
-bash: child setpgid (12745 to 12739): Operation not permitted
-bash: child setpgid (12746 to 12739): Operation not permitted
anaconda-ks.cfg
install.log
install.log.syslog
Why its happening?
Is there any way to get it cleared?
Resolution

Remove definition of DEBUG trap from logging scripts.

Root Cause

There was a logging function:

Raw
log ()
{
    typeset -r WHOIAM=$(who -m);
    typeset -r WHOAMI=$(whoami);
    typeset -r x=$(history 1 |tail -1 );
    [[ $SECONDS -gt 2 ]] && /bin/logger -p local4.debug -t $WHOIAM $WHOAMI $PWD "${x#        }"
}
and DEBUG trap:

Raw
trap 'log' DEBUG
defined in customer's logging scripts.

A known bug causes intermittent errors when a command with pipeline is issued while the DEBUG trap is enabled. The bug was fixed in bash-4.1. The fix cannot be backported to RHEL 5 because of Production 2 Phase Bug Fix inclusion restrictions.

Diagnostic Steps

capture strace:
Raw
# ps
  PID TTY          TIME CMD
 1047 pts/2    00:00:00 bash
 1372 pts/2    00:00:00 ps
# strace -ttfFv -p 1047 -o /tmp/strace.pipe &
# ls | less
# fg
strace -ttfFv -p 1047 -o /tmp/strace.pipe
Process 1047 detached
^C
explore strace.pipe
from grep -E 'execve|clone|exit_group|setpgid' strace.pipe we could see

setpgid() is trying to set process group ID to already exited process - race condition bug?
there are more unexpected processes executed (who, whoami, tail, logger) before spawning ls and the same before spawning less - could be a DEBUG trap?
search bugzilla
Raw
Summary: debug trap
Classification: Red Hat
Component: bash
Product: Red Hat Enterprise Linux 2.1, Red Hat Enterprise Linux 3,
Red Hat Enterprise Linux 4, Red Hat Enterprise Linux 5,
Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7
gives https://bugzilla.redhat.com/show_bug.cgi?id=720464
* check the traps:

Raw
# trap -p
trap -- 'log' DEBUG
check the 'log' command:
Raw
# type log
log is a function
log ()
{
    typeset -r WHOIAM=$(who -m);
    typeset -r WHOAMI=$(whoami);
    typeset -r x=$(history 1 |tail -1 );
    [[ $SECONDS -gt 2 ]] && /bin/logger -p local4.debug -t $WHOIAM $WHOAMI $PWD "${x#        }"
}
explore logging scripts where 'log' is defined
Raw
# set -x
# . /etc/profile &>/tmp/etc_profile.xtrace
# . ~/.bash_profile &>/tmp/bash_profile.xtrace
# . ~/.bash_login &>/tmp/bash_login.xtrace
# . ~/.profile &>/tmp/dot_profile.xtrace
# . ~/.bashrc &>/tmp/dot_bashrc.xtrace
it was also needed to check manually some scripts, that were included with stderr redirection e.g. via line in /etc/profile:
Raw
. /etc/custom_profile 2>/dev/null
so the xtrace of their execution was lost

Product(s)  Red Hat Enterprise Linux Component  bash Category  Troubleshoot Tags  shells
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