Do not launch a shell for each check

[Matthieu Kermagoret]

Hi list,

I'd like to propose a performance patch for Nagios that reduces the
number of Nagios' descendant processes.

The action of launching a single check involves multiple processes :

  - child 1 (not executed if child_processes_fork_twice is disabled)
    - launch child 2
    - waits for child 2 termination

  - child 2
    - reset signal handling
    - launch a shell (connected with a pipe via *popen*)
    - read plugin output from the pipe
    - write plugin output to a file

  - shell
    - executed as /sh -c command/
    - variable expansion
    - globbing
    - every shell stuff you have on the command line
    - launch the check itself

  - check itself
    - the obvious

In this event flow, we found that the shell execution wasn't required
in most cases. So, by avoiding /sh/ we could save fork/exec time and
reduce the number of concurrent processes at the same time. And indeed
shell's magic would still be available using /sh -c/ as the check
command with no performance penalty compared to the current situation.

What do you think about it ?

Best regards,

-- 
Matthieu KERMAGORET | Développeur

mkermagoret at merethis.com

MERETHIS est éditeur du logiciel Centreon.
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