Dear Maintainers,

Thanks for adding a native systemd service!

I noticed that in an autopkgtest-build-qemu VM the service fails:

root@host:~# systemctl status --no-pager -l rng-tools-debian
× rng-tools-debian.service - Hardware RNG entropy gatherer daemon
(Debian variant)
     Loaded: loaded (/usr/lib/systemd/system/rng-tools-debian.service;
enabled; preset: enabled)
     Active: failed (Result: exit-code) since Tue 2025-01-14 12:58:55
UTC; 31s ago
 Invocation: 50bf1d4b6ec64387a27ea1a42c0be118
       Docs: man:rngd(8)
    Process: 441 ExecStart=/usr/share/rng-tools-debian/systemd-helper
start (code=exited, status=1/FAILURE)
   Mem peak: 1.7M
        CPU: 8ms

Jan 14 12:58:55 host systemd[1]: Starting rng-tools-debian.service -
Hardware RNG entropy gatherer daemon (Debian variant)...
Jan 14 12:58:55 host rng-tools-debian[450]: not starting: /dev/hwrng
is used by the kernel automatically
Jan 14 12:58:55 host systemd[1]: rng-tools-debian.service: Control
process exited, code=exited, status=1/FAILURE
Jan 14 12:58:55 host systemd[1]: rng-tools-debian.service: Failed with
result 'exit-code'.
Jan 14 12:58:55 host systemd[1]: Failed to start
rng-tools-debian.service - Hardware RNG entropy gatherer daemon
(Debian variant).

It looks like this is doing some checks, and intends to skip. But just
exiting means the service is recorded as failed, and this will likely
trip other tests, hence the severity to stop migrating to testing for
now.

There are several ways to do such checks natively _and_ resulting in a
service that is skipped, rather than failed.
You could run the script that does the check in an ExecCondition=
statement - if that fails, the service is marked as skipped.

https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#ExecCondition=

Or, you could have a special exit status that means the service is
marked as successful:

https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html#SuccessExitStatus=

There might be other options as well, these are just the first that
came to mind.

Ah, ouch. Agreed.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=504044#162

RestartPreventExitStatus was the one I found and wondered about.

That’s also an option.

Would you mind looking at the aforementioned mail again, as it
also has other questions, and suggest how we best deal with this?

Additionally… what should we do if no random device is found,
as opposed to quietly not starting if one is found that doesn’t
need rngd to run? The sysvinit script will also just exit 0 in
that case, but it doesn’t have service tracking, and a subsequent
status query will show the dæmon as not running, obviously. I’ve
got no idea how this maps best into the systemd ecosystem, though
I’m currently leaning towards making all the “expected not to start”
conditions the same.

Thanks in advance,
//mirabilos

Looking into it now.

Wasn't aware of this. Thanks for the pointers.

Applying ExecCondition to me seems the most reasonable solution to this
bug.

I believe the service should get skipped per ExecCondition also in this
case (no random device found/available).

Sven

Can the script behind ExecCondition pass variables to the script
behind ExecStart or, even better, the unit itself so we can then
use $HRNGDEVICE and $RNGDOPTIONS there?

If not, I’d lean towards one (which?) of the errorlevel-using ones,
because otherwise we’d have to run the detection code twice.

OK.

bye,
//mirabilos

Found no suitable way to achieve this. One can write a file to hold the
variables and their values when checking the conditions, and read it
back when actually starting the service, but this seems a clunky
approach to me.

Not sure what you mean by 'one of the errorlevel-using ones'. Please
explain your idea in more details.

My current solution indeed needs to run the detection code twice.

Sven

SuccessExitStatus or RestartPreventExitStatus, see further above
in the thread.

(I’d also s̲t̲i̲l̲l̲ like input from the systemd maintainers whether
we should exec the binary from the wrapper script or call it in
the background as is currently done.)

Thanks,
//mirabilos


Michael Schmitz on nntp://news.gmane.org/gmane.linux.debian.ports.68k
a.k.a. {news.gmane.org/nntp}#news.gmane.linux.debian.ports.68k in pine

This is an anti-pattern, and best avoided. What's the problem if the
script runs twice? If it just detects things it should be just fine,
no?

Extra effort, though. And, in general, TOCTOU, but probably not
applicable here.

bye,
//mirabilos

Hi Thorsten,

see https://salsa.debian.org/sven-geuer/rng-tools-debian for what,
according to my tests, fixes the issue.

Cheers,
Sven

We believe that the bug you reported is fixed in the latest version of
rng-tools-debian, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1093002@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Thorsten Glaser <tg@mirbsd.de> (supplier of updated rng-tools-debian package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Fri, 17 Jan 2025 01:04:37 +0100
Source: rng-tools-debian
Architecture: source
Version: 2.6
Distribution: unstable
Urgency: low
Maintainer: Thorsten Glaser <tg@mirbsd.de>
Changed-By: Thorsten Glaser <tg@mirbsd.de>
Closes: 1093002
Changes:
 rng-tools-debian (2.6) unstable; urgency=low
 .
   [ Sven Geuer ]
   * Rework d/rng-tools-debian.service and d/systemd-helper:
     - Switch service from Type=forking to Type=exec
     - Terminate the service cleanly in case it decides it cannot run
       (Closes: #1093002)
   * Rename systemd-helper to rngd-systemd-helper
     - Update d/rng-tools-debian.install and d/rng-tools-debian.service for
       referencing the renamed file
   * d/t/*: Adapt autopkgtests to the changes listed above
   * configure.ac: Bump version to 2.6
 .
   [ Thorsten Glaser ]
   * Update autopkgtests restrictions
   * Tell lintian
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