[systemd-devel] [PATCH weston] doc/systemd: system service example

Wed Nov 29 13:40:55 UTC 2017

On Wed, 29 Nov 2017 09:32:02 +0100
Jérémy Rosen <jeremy.rosen at smile.fr> wrote:

> I had a quick glance but didn't actually test...

> 2) you probably want to add Alias=display-manager.service, so it can 
> pull it other graphical services

Hi,

that sounds like a good idea.

Thanks,
pq

(adding back all the CCs)

> On 28/11/2017 11:14, Pekka Paalanen 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.
> > ---
> >   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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