How can I check the config?

We have often seen the case, that someone has rsyslog running and makes changes to the configuration. And usually, after making the changes, rsyslog gets restarted, but the changed config is invalid. rsyslog has a function to check the configuration for validity. This can be done very easily by invoking this command:

rsyslogd -N1

(Note that rsyslogd may not be in your search path – then it usually is found in /sbin/rsyslogd)

This tells rsyslog to do a config check. It does NOT run in regular mode, but just check configuration file correctness. This option is meant to verify a config file. To do so, run rsyslogd interactively in foreground, specifying -f <config-file> and -N level. The level argument modifies behaviour. Currently, 0 is the same as not specifying the -N option at all (so this makes limited sense) and 1 actually activates the code.

This configuration check will only check the configuration for integrity like syntax. Additionaly, the modules will be loaded to make sure that they work properly. On the downside, since the engine will not be loaded, errors with permissions or alike cannot be checked. These will occur only when running rsyslog normally.

The verdict for this option is, that it is quite useful for a first check if the changes were correct, without running the configuration in live mode. This might help to prevent that rsyslog gets restarted with a basically wrong configuration and thus rendering rsyslog useless, because it might not work or not work properly.