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

Solution 1:

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}')"

Solution 2:

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)

Solution 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

Solution 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.

Solution 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 :-(

Tags:

Journalctl

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