That looks again like the problem with the short-lived processes, that the message reaches to journal after the service is already dead. If you add a sleep after the echo, does it fix the issue?

Can't test now (leaving for vacations) but doesn't happen with "runuser" and User=root, so I doubt it's related to short-living processes.

Isn't this a duplicate of https://bugzilla.redhat.com/show_bug.cgi?id=1658115? I believe we tested it on RHEL-7.6 and it worked there, but I might be wrong.

Hi Jan, I don't know if it's BZ 1658115. The PR is for RHEL8 and code changed quite a lot.

Ok, we (I) need to investigate this a bit more thoroughly.

It's clearly not related to BZ #1658115.
After setting some GDB breakpoints, I can see the message goes through this (line numbers from latest RHEL7.6):

-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------
310 static int stdout_stream_line(StdoutStream *s, char *p, LineBreak line_break) {
...
338         case STDOUT_STREAM_UNIT_ID:
339                 if (s->ucred.uid == 0) {
340                         if (isempty(p))
341                                 s->unit_id = NULL;
342                         else  {
343                                 s->unit_id = strdup(p);
344                                 if (!s->unit_id)
345                                         return log_oom();
346                         }
347                 }
348 
349                 s->state = STDOUT_STREAM_PRIORITY;
350                 return 0;
-------- 8< ---------------- 8< ---------------- 8< ---------------- 8< --------

On line 339, when unit is executed by the user, ucred.uid != 0, so s->unit_id remains to NULL (initialized as such in caller), whereas when executed by root (or through "runuser"), ucred.uid == 0, so s->unit_id is set to "p" which is the unit name (e.g. "dummy_root.service").

It's unclear to me why there is that restriction on line 339.

RHEL8 code is similar.

Code introduced in commit 62bca2c657bf95fd1f69935eef09915afa5c69d9:

    journal: set the _SYSTEMD_UNIT field for messages from terminated processes
    
    As described in
    
      https://bugs.freedesktop.org/show_bug.cgi?id=50184
    
    the journal currently doesn't set fields such as _SYSTEMD_UNIT
    properly for messages coming from processes that have already
    terminated.  This means among other things that "systemctl status" may
    not show some of the output of services that wrote messages just
    before they exited.
    
    This patch fixes this by having processes that log to the journal
    write their unit identifier to journald when the connection to
    /run/systemd/journal/stdout is opened.  Journald stores the unit ID
    and uses it to fill in _SYSTEMD_UNIT when it cannot be obtained
    normally (i.e. from the cgroup).  To prevent impersonating another
    unit, this information is only used when the caller is root. 
    
    This doesn't fix the general problem of getting metadata about 
    messages from terminated processes (which requires some kernel
    support), but it allows "systemctl status" and similar queries to do 
    the Right Thing for units that log via stdout/stderr.


"To prevent impersonating another unit, this information is only used when the caller is root."

--> This is why only units running as root get their messages tagged with the unit name.

Again, this can be solved by implementing BZ #1117877

I'm going to move this bug to the RHEL 8 release to match the (somewhat) associated 1117877 tracker. We aren't really going to be able to target this effort in RHEL 7 based on the current point in the lifecycle.

*** Bug 1919275 has been marked as a duplicate of this bug. ***

*** Bug 2061689 has been marked as a duplicate of this bug. ***

*** Bug 1852845 has been marked as a duplicate of this bug. ***

This is still a factor for me in RHEL 9.1. It would be great to see this fixed, enabling cost savings through filtering unnecessary logspam.