The Janitor Process¶
The janitor process carries out periodic cleanup tasks. For example, it is used by omfile to close files after a timeout has expired.
The janitor runs periodically. As such, all tasks carried out via the janitor will be activated based on the interval at which it runs. This means that all janitor-related times set are approximate and should be considered as “no earlier than” (NET). If, for example, you set a timeout to 5 minutes and the janitor is run in 10-minute intervals, the timeout may actually happen after 5 minutes, but it may also take up to 20 minutes for it to be detected.
In general (see note about HUP below), janitor based activities scheduled to occur after n minutes will occur after n and (n + 2*janitorInterval) minutes.
To reduce the potential delay caused by janitor invocation, the interval at which the janitor runs can be be adjusted. If high precision is required, it should be set to one minute. Janitor-based activities will still be NET times, but the time frame will be much smaller. In the example with the file timeout, it would be between 5 and 6 minutes if the janitor is run at a one-minute interval.
Note that the more frequent the janitor is run, the more frequent the system needs to wakeup from potential low power state. This is no issue for data center machines (which usually always run at full speed), but it may be an issue for power-constrained environments like notebooks. For such systems, a higher janitor interval may make sense.
As a special case, sending a HUP signal to rsyslog also activate the janitor process. This can lead to too-frequent wakeups of janitor-related services. However, we don’t expect this to cause any issues. If it does, it could be solved by creating a separate thread for the janitor. But as this takes up some system resources and is not not considered useful, we have not implemented it that way. If the HUP/janitor interaction causes problems, let the rsyslog team know and we can change the implementation.