I have systemd service that runs a bash file. All the output of this script is logger in the systemd journal, and correctly attributed to the corresponding unit by systemd:

# myservice.sh
echo "PROGRESS 1/5"
echo "PROGRESS 2/5"
echo "PROGRESS 3/10"
echo "PROGRESS 9/10"
> journalctl -eu my-service
oct. 19 16:01:38 my-computer systemd[1]: Started My service.
oct. 19 16:01:40 my-computer my-service[137083]: PROGRESS: 1/5
oct. 19 16:01:42 my-computer my-service[137083]: PROGRESS: 2/5
oct. 19 16:01:44 my-computer my-service[137083]: PROGRESS: 3/10
oct. 19 16:01:46 my-computer my-service[137083]: PROGRESS: 9/10
oct. 19 16:01:46 my-computer systemd[1]: my-service.service: Succeeded.

However, I would like to add additional information in my log entries, by adding new fields. I tried to use logger for that without success: the fields are not stored correctly and the logged lines are not flagged as comming from my-service.service.

# myservice.sh
function log_progress() {
    logger --tag my-service --priority user.info \
           --sd-id lcupdater@1 \
           --sd-param "PROGRESS_VALUE=\"$2\"" \
           --sd-param "PROGRESS_TO=\"$3\"" \

log_progress "Doing stuff" 1 5
log_progress "Doing more stuff" 2 5
log_progress "Going on..." 3 10
log_progress "Almost done..." 9 10

> journalctl -e -o json
  "_UID": "0",
  "_GID": "0",
  "_PID": "147370",
  "_SOURCE_REALTIME_TIMESTAMP": "1603120378691356",
  "MESSAGE": "1 2020-10-19T17:12:58.691328+02:00 my-computer my-service - - [timeQuality tzKnown=\"1\" isSynced=\"1\" syncAccuracy=\"132000\"][lcupdater@1 PROGRESS_VALUE=\"9\" PROGRESS_TO=\"10\"] Almost d
  "__MONOTONIC_TIMESTAMP": "28976809066",
  "_TRANSPORT": "syslog",
  "SYSLOG_RAW": "<14>1 2020-10-19T17:12:58.691328+02:00 my-computer my-service - - [timeQuality tzKnown=\"1\" isSynced=\"1\" syncAccuracy=\"132000\"][lcupdater@1 PROGRESS_VALUE=\"9\" PROGRESS_TO=\"10\"] A
lmost done...",
  "PRIORITY": "6",
  "__REALTIME_TIMESTAMP": "1603120378691368"

The field _SYSLOG_UNIT is missing, and PROGRESS_VALUE and PROGRESS_TO are not stored correclty. Is there a way to achieve this?


A verbose but more correct way to achieve this is to use logger --journald:

function log_progress() {
    logger --journald <<EOF

However, the field _SYSTEMD_UNIT is stripped, as only systemd is allowed to manipulate it.

  • Perhaps you'll have better luck outputting data normally, but in your own field-delimited format? Do you really need journalctl to have more fields? What's consuming the journal data on the other end? That process could parse the journal data with its own understanding of fields.
    – Jeff Schaller
    Oct 19 '20 at 16:00
  • I don't really need it, but it would have been cleaner IMO. The receiving application is in C++, I can read fields easily. I'll stick with "PROGRESS: N/M" for now.
    – Hugal31
    Oct 20 '20 at 7:17

It is definitely possible to add additional fields according to the systemd.journal-fields documentation (“New fields may freely be defined by applications, […]” but the only solution I found is using native messaging via the journald-socket and a c-library. I haven't found anything which can easily used within shell-scripts, not even systemd-cat accepts json as input.

As of now, the easiest way is probably to rewrite your application in python and use the systemd.journal-module

  • I cannot add the _SYSTEMD_UNIT field by myself, only systemd is allowed to.
    – Hugal31
    Oct 20 '20 at 8:23
  • 1
    yes, the fields with underscore-prefix are reserved, but you can use OBJECT_SYSTEMD_UNIT (freedesktop.org/software/systemd/man/…)
    – blaimi
    Oct 21 '20 at 10:08

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