02/02: announcements: Add GNOME post.

[Ludovic Court�s]

civodul pushed a commit to branch master
in repository maintenance.

commit 984166211e937fbc517bc9d7723f9b946bc50584
Author: Ludovic Courtès <address@hidden>
Date:   Tue Mar 29 15:30:40 2016 +0200

    announcements: Add GNOME post.
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+GNOME on GuixSD
+
+It’s a feature that many users were waiting for: proper 
[https://www.gnome.org/ GNOME] support in GuixSD.  Good news: the forthcoming 
Guix and GuixSD release will give you exactly that!  Don’t miss the obligatory 
[https://www.gnu.org/software/guix/screenshots/0.9.1/gnome-totem-epiphany.png 
screenshot]!
+
+You would think adding GNOME is routine distro work involving a lot of 
packaging and bits of plumbing that’s already been done a hundred times, which 
is probably true!  Yet, adding GNOME support turned out to be interesting in 
many ways: it’s a good test for GuixSD’s declarative operating system 
configuration framework, it’s a way to formalize how this whole software stack 
fits together, and it’s been an insightful journey into GNU/Linux desktop 
plumbing!
+
+Of course, a lot of software needs to be packaged to begin with.  This had 
been on-going for some time, culminating with the addition of a 
[https://www.gnu.org/software/guix/packages/#gnome gnome meta-package] thanks 
to the hard work of 宋文武 (Sou Bunnbu) and other hackers.  On the way, we added 
[https://lists.gnu.org/archive/html/guix-devel/2015-12/msg00173.html an 
auto-updater for GNOME packages], because all these package recipes need love.
+
+The more interesting parts were system integration.  Modern GNOME/Freedesktop 
environments rely on a number of daemons, most of which talk over 
[https://www.freedesktop.org/wiki/Software/dbus/ D-Bus], and extending each 
other’s functionality: udev, udisks, upower, colord, geoclue, and polkit, to 
name a few.  Being able to _compose_ all these system services was one of the 
driving use cases behind 
[https://savannah.gnu.org/forum/forum.php?forum_id=8412 the design of GuixSD’s 
new service c [...]
+
+Since GuixSD uses the [https://www.gnu.org/software/shepherd/ GNU Shepherd] 
and not systemd as its init system, we needed a way to provide the 
[https://freedesktop.org/wiki/Software/systemd/logind/ “logind”] functionality 
that systemd implements, and which allows GNOME to know about 
[https://www.freedesktop.org/wiki/Software/systemd/multiseat/ users, sessions, 
and seats].
+
+So Andy Wingo courageously started by 
[https://lists.gnu.org/archive/html/guix-devel/2015-04/msg00352.html 
extracting] logind from systemd, leading to [https://github.com/wingo/elogind 
“elogind”].  At this point, we had this daemon that could keep track of 
logged-in users and active sessions, and which GNOME could talk to over D-Bus… 
provided all the relevant [http://www.linux-pam.org/ PAM services] would use 
the pam_elogind module so that elogind knows when a user logs in and out, as An 
[...]
+
+This pam_elogind thing is a typical example of a cross-cutting concern: _if_ 
you use elogind, _then_ you want all the relevant login-related PAM services 
(mingetty, the X login manager, commands such as su, the SSH daemon, etc.) to 
use pam_elogind.  To achieve that, we 
[http://git.savannah.gnu.org/cgit/guix.git/commit/?id=12c00bca92e3eef2b86565924bbefc39397b5497
 updated] our PAM service such that it could be 
[https://lists.gnu.org/archive/html/guix-devel/2016-02/msg00163.html extended] 
w [...]
+
+At this point, the brave could start using GNOME on GuixSD but would soon 
realize that, for example, the “power off” button wouldn’t have the desired 
effect, or that changing a laptop’s backlight wouldn’t work because 
[https://www.freedesktop.org/wiki/Software/polkit/ polkit], the daemon that 
allows unprivileged users to perform privileged operations like that one, was 
[https://lists.gnu.org/archive/html/guix-devel/2016-02/msg01000.html missing 
essential policy files].
+
+You would think you can finally change the brightness of your screen, but no!  
Turns out that polkit would 
[https://lists.gnu.org/archive/html/guix-devel/2016-02/msg01170.html refuse to 
run gnome-setting-daemon’s backlight helper program] because 
[https://lists.gnu.org/archive/html/guix-devel/2016-03/msg00247.html elogind 
happened to fail to map PIDs to sessions].  Whatever.
+
+Of course there were still a bunch of embarrassing glitches such as 
[http://debbugs.gnu.org/cgi/bugreport.cgi?bug=22666 GNOME suspending right 
after it wakes up from suspend], failure to start in QEMU, or 
[https://lists.gnu.org/archive/html/guix-devel/2016-03/msg00690.html the lack 
of GNOME’s favorite font].  Well, it seems that all these are gone now!
+
+GuixSD users can now enable GNOME by adding 
[https://lists.gnu.org/archive/html/guix-devel/2016-03/msg00639.html one line] 
in their 
[https://www.gnu.org/software/guix/manual/html_node/Using-the-Configuration-System.html
 operating system configuration].  Overall, this has been a nice experience 
involving a variety of areas.
+
+== About GNU Guix ==
+
+[http://www.gnu.org/software/guix GNU Guix] is a functional package manager 
for the GNU system.  The Guix System Distribution or GuixSD is an advanced 
distribution of the GNU system that relies on GNU Guix and 
[http://www.gnu.org/distros/free-system-distribution-guidelines.html respects 
the user's freedom].
+
+In addition to standard package management features, Guix supports 
transactional upgrades and roll-backs, unprivileged package management, 
per-user profiles, and garbage collection.  Guix uses low-level mechanisms from 
the Nix package manager, except that packages are defined as native 
[http://www.gnu.org/software/guile Guile] modules, using extensions to the 
[http://schemers.org Scheme] language.  GuixSD offers a declarative approach to 
operating system configuration management, and is  [...]
+
+GuixSD can be used on an i686 or x86_64 machine.  It is also possible to use 
Guix on top of an already installed GNU/Linux system, including on mips64el and 
armv7.