While systemd suggests using the pre-defined graphical-session user
target, I found that this interface is difficult to use. Additionally,
no other major distribution, even in their unstable versions, currently
use this mechanism.
The window or desktop manager is supposed to run in a systemd user service
which activates graphical-session.target and the user services that are
binding to this target. The issue is that we can't elegantly pass the
xsession environment to the window manager session, in particular
whereas the PassEnvironment option does work for DISPLAY, it for some
mysterious reason won't for PATH.
This commit implements a new graphical user target that works just like
default.target. Services which should be run in a graphical session just
need to declare wantedBy graphical.target. The graphical target will be
activated in the xsession before executing the window or display manager.
Fixes#17858.
Before commit 54fa0cfe4e, the `redshift`
service was run with the environment variable `DISPLAY` set to `:0`.
Commit 54fa0cfe4e changed this to
instead use the value of the `services.xserver.display` configuration
option in the value of the `DISPLAY` variable. In so doing, no default
value was provided for the case where `services.xserver.display` is
`null`.
While the default value of `services.xserver.display` is `0`, use of
which by the `redshift` module would result in `DISPLAY` again being
set to `:0`, `services.xserver.display` may also be `null`, to which
value it is set by, e.g., the `lightdm` module.
In the case that `services.xserver.display` is `null`, with the change
made in commit 54fa0cfe4e, the `DISPLAY`
variable in the environment of the `redshift` service would be set to
`:` (a single colon), which, according to my personal experience,
would result in —
- the `redshift` service failing to start; and
- systemd repeatedly attempting to restart the `redshift` service,
looping indefinitely, while the hapless `redshift` spews error
messages into the journal.
It can be observed that the malformed value of `DISPLAY` is likely at
fault for this issue by executing the following commands in an
ordinary shell, with a suitable `redshift` executable, and the X11
display not already tinted:
- `redshift -O 2500` — This command should reduce the color
temperature of the display (making it more reddish).
- `DISPLAY=':' redshift -O 6500` — This command should raise the
color temperature back up, were it not for the `DISPLAY`
environment variable being set to `:` for it, which should cause
it to, instead, fail with several error messages.
This commit attempts to fix this issue by having the `DISPLAY`
environment variable for the `redshift` service default to its old
value of `:0` in the case that `services.xserver.display` is `null`.
I have tested this solution on NixOS, albeit without the benefit of a
system with multiple displays.
- add missing types in module definitions
- add missing 'defaultText' in module definitions
- wrap example with 'literalExample' where necessary in module definitions
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
The redshift service stops working after some time (the program exits
after some hours/days). It looks like these exits are related to calls
to xrandr (for multiple displays) or suspend-to-ram.
Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
