omprog: Program integration Output module

Module Name:    omprog

Available since: 4.3.0

Author:Rainer Gerhards <rgerhards@adiscon.com>

Description:

This module permits to integrate arbitrary external programs into rsyslog’s logging. It is similar to the “execute program (^)” action, but offers better security and much higher performance. While “execute program (^)” can be a useful tool for executing programs if rare events occur, omprog can be used to provide massive amounts of log data to a program.

Executes the configured program and feeds log messages to that binary via stdin. The binary is free to do whatever it wants with the supplied data. If the program terminates, it is re-started. If rsyslog terminates, the program’s stdin will see EOF. The program must then terminate. The message format passed to the program can, as usual, be modified by defining rsyslog templates.

Note that each time an omprog action is defined, the corresponding program is invoked. A single instance is not being re-used. There are arguments pro and con for re-using existing binaries. For the time being, it simply is not done. In the future, we may add an option for such pooling, provided that some demand for that is voiced. You can also mimic the same effect by defining multiple rulesets and including them.

Note that in order to execute the given program, rsyslog needs to have sufficient permissions on the binary file. This is especially true if not running as root. Also, keep in mind that default SELinux policies most probably do not permit rsyslogd to execute arbitrary binaries. As such, permissions must be appropriately added. Note that SELinux restrictions also apply if rsyslogd runs under root. To check if a problem is SELinux-related, you can temporarily disable SELinux and retry. If it then works, you know for sure you have a SELinux issue.

Starting with 8.4.0, rsyslogd emits an error message via the syslog() API call when there is a problem executing the binary. This can be extremely valuable in troubleshooting. For those technically savy: when we execute a binary, we need to fork, and we do not have full access to rsyslog’s usual error-reporting capabilities after the fork. As the actual execution must happen after the fork, we cannot use the default error logger to emit the error message. As such, we use syslog(). In most cases, there is no real difference between both methods. However, if you run multiple rsyslog instances, the messae shows up in that instance that processes the default log socket, which may be different from the one where the error occured. Also, if you redirected the log destination, that redirection may not work as expected.

Module Parameters:

  • Template[templateName]

    sets a new default template for file actions.

Action Parameters:

  • binary Mostly equivalent to the “binary” action parameter, but must contain the binary name only. In legacy config, it is not possible to specify command line parameters.

  • hup.signal [v8.9.0+] Specifies which signal, if any, is to be forwarded to the executed program. Currently, HUP, USR1, USR2, INT, and TERM are supported. If unset, no signal is sent on HUP. This is the default and what pre 8.9.0 versions did.

  • signalOnClose [switch] [v8.23.0+] Default: off

    Signal the child process when worker-instance is stopped or Rsyslog is about to shutdown. To signal shutdown, SIGTERM is issued to child and Rsyslog reaps the process before proceeding.

    No signal is issued if this switch is set to ‘off’ (default). The child-process can still detect shutdown because ‘read’ from stdin would EOF. However its possible to have process-leak due to careless error-handling around read. Rsyslog won’t try to reap the child process in this case.

    Additionaly, this controls the following GNU/Linux specific behavior: If ‘on’, Rsyslog waits for upto 5 seconds for child process to terminate after issuing SIGTERM, after which a SIGKILL is issued ensuring child-death. This ensures even an unresponsive child is reaped before shutdown.

Caveats/Known Bugs:

  • None.

Sample:

The following command writes all syslog messages into a file.

module(load="omprog")
action(type="omprog"
       binary="/pathto/omprog.py --parm1=\"value 1\" --parm2=\"value2\""
       template="RSYSLOG_TraditionalFileFormat")

Legacy Configuration Directives:

  • $ActionOMProgBinary <binary> The binary program to be executed.

Caveats/Known Bugs:

Currently none known.

This documentation is part of the rsyslog project. Copyright © 2008-2014 by Rainer Gerhards and Adiscon. Released under the GNU GPL version 3 or higher.

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