Systemd Journal log from command line to specific namespace

Question

How to log from command line to a specific systemd log namespace?

When using Systemd to start a service, one can give LogNamespace=myNamespace in combination with StandardOutput=journal as part of the configuration in the unit file.

To see the output of this namespace, it is sufficient to call journalctl --namespace=myNamespace to see only output of this namespace.

With systemd-catit is possible to print directly from command line into the journal: echo "Hello Journal!" | systemd-cat

The print "Hello Journal!" does show up in the default (anonymous?) namespace, which is visible with journalctl. It is not within any namespace and not visible when using journalctl --namespace=myNamespace.

To be more specific on the initial question: When looking at journalct -f --namespace=myNamespace, how to make the output of a process started from command line (without systemd, just plain binary) visible in this view?

Something like echo "Hello Journal!" | systemd-cat --log-namespace=myNamespace

I use LogNamespaces to separate different application logs. If this is not the intended use, an answer which explains how to this in another (better) way is also accepted.

Answer 1

first find out the pid of your journald with your namespace.

ps aux|grep jou
root         243  0.0  0.6  56176 26212 ?        Ss   10:06   0:01 /lib/systemd/systemd-journald
root       10214  0.0  0.3  42308 14740 ?        Ss   11:34   0:00 /lib/systemd/systemd-journald DEBUG

our instance is DEBUG next find out what socket that instance uses:

lsof -p 10214 |grep dev-log
systemd-j 10214 root    5u     unix 0x0000000003787334      0t0   61560 /run/systemd/journal.DEBUG/dev-log type=DGRAM

now we are ready to log to the desired namespace:

logger -u /run/systemd/journal.DEBUG/dev-log HAHAHAHA

journalctl --namespace=DEBUG
Jan 22 11:35:46 myportal-deb root[10339]: HAHAHAHA
Jan 22 11:38:50 myportal-deb root[10559]: HAHAHAHA