Let's make sure logind is accessible by the time user@.service runs, and
that logind stays around as long as it does so.
Addresses an issue reported here:
https://lists.freedesktop.org/archives/systemd-devel/2024-June/050468.html
This addresses an issued introduced by
278e815bfa, which dropped the a dependency
from user@.service systemd-user-sessions.service without replacement.
While dropping that dependency does make sense, it should have been
replaced with the weaker dependency on systemd-logind.service, hence fix
that now.
user@.service is after all a logind concept, hence logind really should
be around for its lifetime.
systemd-user-sessions.service is a later milestone that only really
should apply to regular users (not root), hence it's too strong a
requirement.
Before #30884, the user state is tied to user@.service (user service
manager). However, #30884 introduced sessions that need no manager,
and we can no longer rely on that.
Consider the following situation:
1. A 'background-light' session '1' is created (i.e. no user service manager
is needed)
2. Session '1' scope unit pulls in user-runtime-dir@.service
3. Session '1' exits. A stop job is enqueued for user-runtime-dir@.service
due to StopWhenUnneeded=yes
4. At the same time, another session '2' which requires user manager is started.
However, session scope units have JobMode=fail, therefore the start job
for user-runtime-dir@.service that was pulled in by session '2' scope job
is deleted as it conflicts with the stop job.
We want session scope units to continue using JobMode=fail, but we still need
the dependencies to be started correctly, i.e. explicitly requested by logind
beforehand. Therefore, let's stop using StopWhenUnneeded=yes for
user-runtime-dir@.service, and track users' `started` and `stopping` state
based on that when user@.service is not needed. Then, for every invocation
of user_start(), we'll recheck if we need the service manager and start it
if so.
Also, the dependency type on user-runtime-dir@.service from user@.service
is upgraded to `BindsTo=`, in order to ensure that when logind stops the
former, the latter is stopped as well.
If for any reason something goes wrong during the boot process (most likely due
to a network issue), system admins should be allowed to log in to the system to
debug the problem. However due to the login session barrier enforced by
systemd-user-sessions.service for all users, logins for root will be delayed
until a (dbus) timeout expires. Beside being confusing, it's not a nice user
experience to wait for an indefinite period of time (no message is shown) this
and also suggests that something went wrong in the background.
The reason of this delay is due to the fact that all units involved in the
creation of a user session are ordered after systemd-user-sessions.service,
which is subject to network issues. If root needs to log in at that time,
logind is requested to create a new session (via pam_systemd), which ultimately
ends up waiting for systemd-user-session.service to be activated. This has the
bad side effect to block login for root until the dbus call done by pam_systemd
times out and the PAM stack proceeds anyways.
To solve this problem, this patch orders the session scope units and the user
instances only after systemd-user-sessions.service for unprivileged users only.
We don't need two (and half) templating systems anymore, yay!
I'm keeping the changes minimal, to make the diff manageable. Some enhancements
due to a better templating system might be possible in the future.
For handling of '## ' — see the next commit.
So far we always used "yes" instead of "true" in all our unit files,
except for one outlier. Let's do this here too. No change in behaviour
whatsoever, except that it looks prettier ;-)
I think this is a slightly cleaner approach than parsing the
configuration file at multiple places, as this way there's only a single
reload cycle for logind.conf, and that's systemd-logind.service's
runtime.
This means that logind and dbus become a requirement of
user-runtime-dir, but given that XDG_RUNTIME_DIR is not set anyway
without logind and dbus around this isn't really any limitation.
This also simplifies linking a bit as this means user-runtime-dir
doesn't have to link against any code of logind itself.
Let's not use the word "wrapper", as it's not clear what that is, and in
some way any unit file is a "wrapper"... let's simply say that it's
about the runtime directory.
Followup to commit 13cf422e04 ("user@.service: don't kill user manager at runlevel switch")
I think there's a general rule that units with `StopWhenUnneeded=yes` need
`IgnoreOnIsolate=yes`... But it doesn't apply to `suspend.target` and friends.
`printer.target` and friends break on isolate even if we apply the rule[1].
That just leaves `graphical-session.target`, which is a user service.
"isolate" is *mostly* a weird attempt to emulate runlevels, so I decided
not to worry about it for user services.
[1] https://github.com/systemd/systemd/issues/6505#issuecomment-320644819
This service won't use much resources, but it's certainly nicer to see
it attached th the user's slice along with user@.service, so that
everything we run for a specific user is properly bound into one unit.
We use systemd-user-sessions.service as barrier when to allow login
sessions. With this patch user@.service is ordered after that too, so
that any login related code (which user-runtime-dir@.service is) is
guaranteed to run after the barrier, and never before.
Unfortunately this needs a new binary to do the mount because there's just
too many special steps to outsource this to systemd-mount:
- EPERM needs to be treated specially
- UserRuntimeDir= setting must be obeyed
- SELinux label must be adjusted
This allows user@.service to be started independently of logind.
So 'systemctl start user@nnn' will start the user manager for user nnn.
Logind will start it too when the user logs in, and will stop it (unless
lingering is enabled) when the user logs out.
Fixes#7339.
