journald: provide a journal distinction per unit file / service for vacuum / disk-size

Submission type

• Bug report
• [X ] Request for enhancement (RFE)

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systemd version the issue has been seen with

231

NOTE: Do not submit bug reports about anything but the two most recently released systemd versions upstream!

Used distribution

Fedora 25

The idea is that user might be able to run journalctl --disk-size -u some.service and also journalctl --vacuum-size=100M -u some.service.

The expected behavior would be in the first case showing size of journal that was taken by specified service. In the latter one expected behavior would be vacuuming size of choosen service up to 100Mb

Case is that when having multiple services running on same host, sometimes we'd like to enable more rich logging for one service (e.g. for live debugging session). After debugging session is done we'd like to clean-up journal to free disk - space; but we're interested only in recovering disk - space taken by those very logs from debugging session to make sure that other's services logs are not affected by vacuum in the nearest future.

Start with the journalctl --disk-size -u and --vacuum-size=100M -u behaviors described in the issue, and inspect how unit filtering and journal size or vacuum operations are currently handled. Done means reporting journal size for the selected service and limiting cleanup to that service without affecting other services.