[PATCH weston] doc/systemd: system service example

Mon Mar 11 08:28:44 UTC 2019

On Tue, 28 Nov 2017 12:14:29 +0200
Pekka Paalanen <ppaalanen at gmail.com> wrote:

> From: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> 
> There are many bad and even worse attempts to make Weston run as a
> systemd service, and very few good ones. Let's add a good one as an
> example in upstream: does not use weston-launch, does not run weston as
> root, does not need wrapper scripts, and relies on logind and PAM.
> 
> This example has been composed from a couple of real-world Weston unit
> files used in production. It has not been used verbatim, but it has been
> briefly tested on one Yocto-based system.
> 
> The service file is not installed by the build. It would likely need
> small adjustments for each distribution or system to be deplyed on.
> 
> The session-c1.scope workaround refers to a systemd bug that has been
> said to be hard to reproduce, but the details have been lost in time.
> 
> Fixes: https://phabricator.freedesktop.org/T63
> 
> Cc: martyn.welch at collabora.co.uk
> Cc: fabien.lahoudere at collabora.co.uk
> Cc: matt.hoosier at gmail.com
> Cc: sjoerd.simons at collabora.co.uk
> Signed-off-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
> 
> ---
> 
> Hi all,
> 
> I have cross-posted this patch to systemd-devel with the hope that
> someone would recall details about the systemd or PAM plugin race that
> prompted the session-c1.scope workaround. I belive Martyn spoke about it
> in person with Lennart, but as far as Martyn recalls, there is no record
> of the issue. Enabling session lingering was mentioned as another
> workaround.

Hi all,

I was recently contacted asking about what happened to this patch. It
still hasn't landed in Weston in any form, because this good discussion
around November 2017 - January 2018 had suggestions I have not had the
time to integrate. I did do a few changes, and the latest is currently
tracked at:

https://gitlab.freedesktop.org/wayland/weston/merge_requests/39

The lacking bits are those particularly around PAM and the old system
specific workaround that is still present.

I would be happy if someone wants to take over this, as it is unlikely
I can push it forward or test meaningfully myself.

Thanks,
pq

> ---
>  doc/systemd/README         | 45 +++++++++++++++++++++++++++++++
>  doc/systemd/weston.service | 66 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 111 insertions(+)
>  create mode 100644 doc/systemd/README
>  create mode 100644 doc/systemd/weston.service
> 
> diff --git a/doc/systemd/README b/doc/systemd/README
> new file mode 100644
> index 00000000..2aa3aa9a
> --- /dev/null
> +++ b/doc/systemd/README
> @@ -0,0 +1,45 @@
> +		Systemd integration examples
> +
> +These examples rely on Weston's logind and systemd support. Weston needs to be
> +built with options: --enable-dbus --enable-systemd-login --enable-systemd-notify
> +
> +Furthermore, Weston needs to be configured to load systemd-notify.so plugin.
> +This can be done on the Weston command line:
> +
> +$ weston --modules=systemd-notify.so
> +
> +or in weston.ini:
> +
> +[core]
> +modules=systemd-notify.so
> +
> +The plugin implements the systemd service notification protocol, watchdog
> +protocol, and also allows socket activation and configuring listening sockets
> +via systemd.
> +
> +
> +	weston.service
> +
> +An example on how to run Weston as a system service. It starts a full user
> +session of the named user on the given virtual terminal.
> +
> +This is useful for running a login manager or for dedicated systems that do not
> +have personal user accounts and do not need the user to log in.
> +
> +You should very least customize the user, but likely also the tty and
> +and the weston command line. See 'systemctl edit' command for an easy way to
> +do that per-system if you don't edit the service file before installing it.
> +
> +This approach has an issue that in one system was worked around with the
> +"After=session-c1.scope" directive. The details have been forgotten, but
> +enabling session lingering was mentioned as another workaround. It might
> +perhaps have something to do with multiple system units triggering the setup
> +of a user session. It would be much better to start Weston as a systemd user
> +service instead to avoid the issue completely.
> +
> +
> +TODO: add an example of socket activation and defining sockets with systemd
> +
> +TODO: talk about starting Weston as a systemd user service, as that would
> +often be more appropriate than as a system service. The user can still be
> +automatically logged in. Presumably the auto-login service can allocate the VT.
> diff --git a/doc/systemd/weston.service b/doc/systemd/weston.service
> new file mode 100644
> index 00000000..80d242a6
> --- /dev/null
> +++ b/doc/systemd/weston.service
> @@ -0,0 +1,66 @@
> +# This is a system unit for launching Weston with auto-login as the
> +# user configured here.
> +#
> +# Weston must be built with systemd support, and your weston.ini must load
> +# the plugin systemd-notify.so.
> +
> +[Unit]
> +Description=Weston, a Wayland compositor, as a system service
> +Documentation=man:weston(1) man:weston.ini(5)
> +Documentation=http://wayland.freedesktop.org/
> +
> +# Make sure we are started after logins are permitted.
> +After=systemd-user-sessions.service
> +
> +# If Plymouth is used, we want to start when it is on its way out.
> +After=plymouth-quit-wait.service
> +
> +# D-Bus is necessary for contacting logind. Logind is required.
> +Wants=dbus.socket
> +After=dbus.socket
> +
> +# This scope is created by pam_systemd when logging in as the user.
> +# This directive is a workaround to a systemd bug, where the setup of the
> +# user session by PAM has some race condition, possibly leading to a failure.
> +# See README for more details.
> +After=session-c1.scope
> +
> +# Since we are part of the graphical session, make sure we are started before
> +# it is complete.
> +Before=graphical.target
> +
> +# Prevent starting on systems without virtual consoles, Weston requires one
> +# for now.
> +ConditionPathExists=/dev/tty0
> +
> +[Service]
> +
> +# Requires systemd-notify.so Weston plugin.
> +Type=notify
> +ExecStart=/usr/bin/weston
> +
> +# Optional watchdog setup
> +TimeoutStartSec=60
> +WatchdogSec=20
> +
> +# The user to run Weston as.
> +User=westonuser
> +
> +# Set up a full user session for the user, required by Weston.
> +PAMName=login
> +
> +# A virtual terminal is needed.
> +TTYPath=/dev/tty7
> +TTYReset=yes
> +TTYVHangup=yes
> +TTYVTDisallocate=yes
> +
> +# Fail to start if not controlling the tty.
> +StandardInput=tty-fail
> +
> +# Log this user with utmp, letting it show up with commands 'w' and 'who'.
> +UtmpIdentifier=tty7
> +UtmpMode=user
> +
> +[install]
> +WantedBy=graphical.target

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