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Accepted
Jack O'Connor
Asked: 2016-04-08 12:48:40 +0800 CST

Is there a way to make journalctl show logs from "the last time foo.service ran"?

  • 772

I'm particularly interested in this for looking at the output of oneshot services that run on a timer. The --unit flag is close, but it concatenates all the runs of the service together. The most obvious way I can think of would be to filter on PID, but that makes me worry about PID reuse / services that fork, and getting the last PID is pretty inconvenient. Is there some other identifier that corresponds to a single run of a service, that I could use to filter the logs?

EDIT: I would happily accept an authoritative "no" if that's the real answer.

journalctl

6 Answers

  1. Best Answer

    Since systemd version 232, we have the concept of invocation ID. Each time a unit is ran, it has a unique 128 bit invocation ID. Unlike MainPID which can be recycled, or ActiveEnterTimestamp which can have resolution troubles, it is a failsafe way to get all the log of a particular systemd unit invocation.

    To obtain the latest invocation ID of a unit

    $ systemctl show --value -p InvocationID openipmi
bd3eb84c3aa74169a3dcad2af183885b

    To obtain the journal of the latest invocation of, say, openipmi, whether it failed or not, you can use the one liner

    $ journalctl _SYSTEMD_INVOCATION_ID=`systemctl show -p InvocationID --value openipmi.service`
-- Logs begin at Thu 2018-07-26 12:09:57 IDT, end at Mon 2019-07-08 01:32:50 IDT. --
Jun 21 13:03:13 build03.lbits openipmi[1552]:  * Starting ipmi drivers
Jun 21 13:03:13 build03.lbits openipmi[1552]:    ...fail!
Jun 21 13:03:13 build03.lbits openipmi[1552]:    ...done.

    (Note that the --value is available since systemd 230, older than InvocationID)

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  2. I'm not sure which timestamp makes the most sense but this works for me. Hopefully there is a better way of working with the timestamps from systemctl show than awk - could not figure out how to control the format of timestamps.

    unit=foo.service

ts=$(systemctl show -p ActiveEnterTimestamp $unit)

echo $ts
ActiveEnterTimestamp=Fri 2016-11-11 12:30:01 MST

journalctl -u $unit --since "$(echo $ts | awk '{print $2 $3}')"
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  3. You can use the boot flag to fetch only the logs from that boot. for instance 

    journalctl _SYSTEMD_UNIT=avahi-daemon.service -b 5
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  4. These might help you:

    • journalctl -u foo.service | tail -n 2

      or replace 2 with expected number of lines

    • journalctl -u foo.service --since='2016-04-11 13:00:00'

    You can as well combine them to get firstly the last run time timestamp, and then use that timestamp with the --since switch.

    • 4

  5. You can use field filters with Journalctl. E.g.

    journalctl _PID=1234

    Get a list of all the available fields using:

    journalctl --fields --unit kubelet

    One available field is _PID.

    You can get the PID of a running process using pidof or systemctl show --property MainPID <SERVICE_NAME>

    So here's how I get the logs from the current Kubernetes kubelet process:

    # journalctl --unit kubelet _PID=$(systemctl show --property MainPID kubelet 2>/dev/null | cut -d= -f2) | head

    Now tell me why I Kubernetes is so hard to install :-(

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  6. journalctl -r | grep -m1 foo.service

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