journalctl -u 'xxx' - add switch to show logs since unit restart

[zabbal]

When debugging misbehaving service which you've got to restart after changing configuration it's really handy to be able to see just the logs from latest run - I mean after running "systemctl restart xxx".

The unit is restarted by systemd so it "knows" when it happened precisely. Would be great if I could use this from within journalctl as well without manually copy-pasting time back and forth. Smth like:
journalctl -u xxx --since-unit-restart

It's in essence similar to journalctl -b but on per-unit, not per-system basis.

[keszybz]

For added points, it should be possible to generate a list of restarts, something analogous to --list-boots.

[towolf]

I had to make a really hacky bash script to achieve something similar.

Somehow the 'big race' in journal that remains a big problem, also plays into this.

Journal seems to have no good way of correlating service start and journal timestamps.

#!/bin/bash
#

[ "${FLOCKER}" != "$0" ] && exec env FLOCKER="$0" flock -en "$0" "$0" "$@" || :

# Timestamp when unit transitioned from inactive to active
since=$(systemctl show -p InactiveExitTimestamp "$1" | cut -f 2 -d '=' | cut -f 2-3 -d' ')
# or one minute if unset
since=${since:-1 min ago}

# Get prefix string that this units logs with: most robust
# https://github.com/systemd/systemd/issues/2913#issuecomment-219702148
id=$(systemctl show -p SyslogIdentifier "$1" | cut -f 2 -d '=')

# Get all raw output from unit since start, only from stdout&stderr
# Considering that backend only logs "bad" stack traces to stderr, this should
# always be relevant
service_trace=$(journalctl -o cat --since "$since" -t "$id")

[fsateler]

It should probably make use of _SYSTEMD_INVOCATION_ID as introduced by #4067

[towolf]

I don't have that field in my journal yet. Version is 229.

[dvaerum]

This feature would be very useful, just to draw some attention to this request 😅

[sedrubal]

It should probably make use of _SYSTEMD_INVOCATION_ID as introduced by #4067

Is there an easy way to get the invocation id of a unit? Something like --list-boots?

[laurivosandi]

Systemd never ceases to surprise how obscure overengineered features get prioritized over very basic usability features

journalctl -u foobar.service  _SYSTEMD_INVOCATION_ID="$(systemctl show -p InvocationID --value foobar.service)"

This should be the default for journalctl -u foobar

[SjonHortensius]

@laurivosandi you are free to send a PR to implement this, right? Also, what constitutes a basic feature versus an obscure feature seems pretty subjective to me.

Your oneliner is pretty nice by the way, I'll make an alias out of it