If you are storing to disk you can increase the amount of space used by changing
SystemKeepFree. Having more space would allow more entries to be stored.
By default the maximum use limit (
SystemMaxUse) is 10% of the filesystem, and the minimum free space (
SystemKeepFree) value is 15% - though they are both capped at 4G.
The journals should be rotated automatically when they reach the
SystemMaxFileSize value, and the number of journals is controlled by
SystemMaxFiles. If you prefer time based rotation you can set a
MaxFileSec to set the maximum time entries are stored in a single journal.
Note on Storage Location/Type
With journald you can choose to store the journal entries either in memory (
Storage=volatile) or on disk (
Storage=persistent). The above assumes you are storing journals on disk - if this is not the case "System" will need to be replaced by "Runtime" in the above variables.
Further details are available in
Alternative - Passing on the journal entries
If you are already familiar with the traditional SYSLOG daemon you can pass the journal events on by setting the
ForwardToSyslog option (which forwards the messages immediately) or have the syslog daemon bahave like a journal client and fetch the logs itself.