`daemon: failed to set user environment` when using daemon(8) with -u and rc script with a user set

[mariachi]

The forgejo-runner port is broken since a recent update. I am waiting for a bugzilla account to submit a bug report and a patch. However, before that I need to understand why this is happening:

• Starting act_runner directly as root (i.e., without daemon(8)) works correctly. -> no surprises here
• Running daemon(8) inside act_runner_prestart also (as done up to version 9.1.0_4 of the port) also works (act_runner would start but in some situations would terminate and remain stopped — this is the original reason for the patch linked above).

Since the patch, the daemon is started with $command outside of act_runner_prestart (I omitted some parts of the patch to focus on the relevant bits):

-command="${procname} ${act_runner_flags}"
+command="/usr/sbin/daemon"
 
-start_cmd="${name}_start"

-act_runner_start() {

+act_runner_prestart() {
   #  ensure the log directories are owned by the unprivileged user
   for d in "${act_runner_log_dir}"; do
     if [ ! -e "$d" ]; then
@@ -42,11 +44,12 @@
       chown "${act_runner_user}" "$d"
     fi
   done
-  /usr/sbin/daemon -S -l "${act_runner_facility}" -s "${act_runner_priority}" \
-    -T "${name}" \
-    -u "${act_runner_user}" -p "${pidfile}" \
-    -o "${act_runner_log_file}" \
-    $command
}
+
+command_args=" -r -S -l ${act_runner_facility} -s ${act_runner_priority} \
+    -T ${name} \
+    -u ${act_runner_user} -P ${pidfile} \
+    -o ${act_runner_log_file} \
+    ${exec_path} ${act_runner_args}"

Running the script like this results in "daemon: failed to set user environment" in the logs.

To fix this, the only change needed was to remove -u ${act_runner_user} from the daemon incantation — why, and is it even fixing the "right thing"?

Some more context:

• the act_runner user exists and its home is owned by act_runner

pw user show act_runner
act_runner:*:806:806::0:0:Act Runner User:/var/db/act_runner:/usr/sbin/nologin