Bash does not represent current pid and parent process-id correctly
in spawned processes.
The configuration information below is from a RedHat 9.0 system,
but I have confirmed the problem still exists using
bash version 3.1.17(1)-release on Fedora Core 6.
Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: linux-gnu
Compiler: i386-redhat-linux-gcc
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='i386'
-DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='i386-redhat-linux-gnu'
-DCONF_VENDOR='redhat' -DSHELL -DHAVE_CONFIG_H -I. -I. -I./include -I./lib
-D_GNU_SOURCE -O2 -march=i386 -mcpu=i686 -g
uname output: Linux skywalker.ca.boeing.com 2.4.20-8 #1 Thu Mar 13 17:54:28 EST
2003 i686 i686 i386 GNU/Linux
Machine Type: i386-redhat-linux-gnu
Bash Version: 2.05b
Patch Level: 0
Release Status: release
Description:
[Detailed description of the problem, suggestion, or complaint.]
The shell variables $$ and $PPID are not correct in child shell
processes spawned by a parent shell process.
Repeat-By:
[Describe the sequence of events that causes the problem
to occur.]
This script will demonstrate the problem:
-cut here--
#!/bin/sh
#
# 4/9/07 - Stan Tazuma
#
# demo of bash bugs in the use of:
# $$ $PPID
demo1() {
echo function in forked process shows pid='$$' of original process,
echo not the new child process
echo demo1: pid=$$, PPID=$PPID
}
demo2() {
echo pipe situation -- the processes in the pipe should be able to
echo determine their own pid, but they cannot
some_var='some'
(echo demo2/pipe-writer: pid = $$, PPID = $PPID) |
(
read line
echo $line
# neither $$ nor $PPID appear to be evaluated at run-time,
# but are just kept as they were from the parent shell;
# since neither are environment variables, that is strange
echo demo2/pipe-reader: pid = $$, PPID = $PPID
# the next few lines show that other variables
# are being evaluated at run time
echo some_var=$some_var
some_var=something
echo some_var=$some_var
)
}
echo ==
echo parent pid = $$, PPID = $PPID
echo ==
echo calling demo1 in a background process ...
demo1 &
wait
echo ''
echo ==
echo calling demo2 ...
demo2
echo ''
echo ==
echo A situation where you need an accurate listing of pids:
echo You have a tree of processes for a system service, and you
echo want a reliable way of killing off all the processes started
echo for that service. I would like to have each process write its
echo own pid to a pid file.
echo ''
-cut here--
Running the above script results in:
==
parent pid = 8291, PPID = 30730
==
calling demo1 in a background process ...
function in forked process shows pid=$$ of original process,
not the new child process
demo1: pid=8291, PPID=30730
==
calling demo2 ...
pipe situation -- the processes in the pipe should be able to
determine their own pid, but they cannot
demo2/pipe-writer: pid = 8291, PPID = 30730
demo2/pipe-reader: pid = 8291, PPID = 30730
some_var=some
some_var=something
==
A situation where you need an accurate listing of pids:
You have a tree of processes for a system service, and you
want a reliable way of killing off all the processes started
for that service. I would like to have each process write its
own pid to a pid file.
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