upstart loses track of process ID when /etc/default/ entry contains backticks

[Simon Fraser]

Initially noticed with our autofs5 configuration, which uses `uname ` to set some architecture specific options for a software distribution mount.

If /etc/default/testapp contains an entry like:
OPTION=`uname -m`

Then upstart gets the wrong PID for the daemon. This means we can't stop/restart the service, and shutting down the machine is impossible without resetting the power - upstart hangs looking for the wrong process ID.

# status testapp
testapp start/running, process 854
# ps -ef | grep testapp
root 855 1 0 15:04 ? 00:00:00 /root/testapp

Take the backticks out of /etc/default/testapp and things work as expected.

# cat testapp.c
#include <sys/types.h>

int main(void) {
 pid_t pid = fork();
 if ( pid == 0 ) {
  while(1) {
   sleep(10);
  }
 } else {
  return(0);
 }
}

# cat /etc/default/testapp
OPTION=`uname -m`
# cat /etc/init/testapp.conf
description "Test Application"
author "<email address hidden>"

start on runlevel [2345]
stop on runlevel [!2345]

expect fork # have also tried 'expect daemon'
respawn

script
    if [ -f /etc/default/testapp ] ; then
        . /etc/default/testapp
    fi
    exec /root/testapp
end script

lsb_release -rd
Description: Ubuntu 12.04 LTS
Release: 12.04

# apt-cache policy upstart
upstart:
  Installed: 1.5-0ubuntu5
  Candidate: 1.5-0ubuntu7
  Version table:
     1.5-0ubuntu7 0
        500 http://gb.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
 *** 1.5-0ubuntu5 0
        500 http://gb.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/status

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.