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Redshift

For anyone who can't resist using the computer at night, redshift can seem like a godsend, turning the midnight sun of your monitor into a cozy hearthfire. Here (as of Jessie) are a couple of snags to watch out for.

Hardware cursor too hot

Some video drivers offload the cursor to the hardware -- your graphics card -- because it's much faster. But a program like Redshift works at the software level, which means your hardware-drawn cursor will stay white-hot no matter the time of day. To fix that, you can tell X to disable the hardware cursor by adding a file to /etc/X11/xorg.conf.d:

    Section "Device"
        Identifier "Screen 0"
        Driver "nouveau"
        Option "HWCursor" "false"
    EndSection

The identifier (name of the display device), the driver name, and even the option syntax will vary depending on your hardware. Here's how you might confirm:

    $ xrandr
    Screen 0: minimum 320 x 200 ...
    $ lsmod | grep ^video
    video                  18096  1 nouveau
    $ apropos nouveau
    nouveau (4)          - NVIDIA video driver
    $ man 4 nouveau
    ... refer to xorg.conf(5) for general configuration details....
    $ man 5 xorg.conf

Changes won't take effect until you reboot (or otherwise restart the X server).

Switching to a software cursor may turn your mouse pointer into a glitch wand; depending on your system and your sensitivities, the extra flickering may be an unacceptable trade-off. Then again, some of the side effects may be welcome: if you've ever roused a sleeping display to find that your cursor has disappeared, switching the cursor may be just the thing.

There are other ways to check the video driver (sifting through /var/log/Xorg.0.log, for instance) and to confirm the device identifier (running Xorg -configure, if possible), but let's leave those topics to other pages and continue.

Display manager not affected

If you set Redshift to start when you log in -- whether by adding it as a start-up program in your desktop environment or with a redshift & in your .xsessionrc -- logging out can be like turning on the floodlights. Fortunately, some display managers let you specify start-up programs, too. Here's how you might arrange it with LightDM:

    $ sudo ed -s /etc/lightdm/lightdm.conf
    ?display-setup-script?c
    display-setup-script=/etc/lightdm/redshift
    .
    wq
    $ sudo sh -c "cat > /etc/lightdm/redshift"
    #! /bin/sh

    if type redshift; then
        redshift -l -23.2:-71.3 -t 6400:3700 -r &
    fi
    $ sudo chmod +x /etc/lightdm/redshift

Rather than cramming all the options onto the command line, you may prefer to create a system-wide configuration file instead, either at /etc/redshift.conf or in XDG_CONFIG_DIRS if you've set them.

See also