Linux: Permanent graphics mode (resolution) on Cinnamon
The goal
Quite simple: Set a fixed graphics mode on the computer screen.
More precisely, make Cinnamon (version 3.2.6) on Linux Mint 18.1 (Serena) show the desktop with a predefined resolution, no matter what happens. Spoiler: I failed. But I got close enough for practical purposes, and collected a lot of knowledge while trying. So here it is.
The reason I need this: On the machine mentioned here, I have an two screens connected through an HDMI splitter, so the monitor identification is somewhat shaky, and it’s not clear which piece of info the computer gets each time. To make it even trickier, the graphics mode I need is only listed in the EDID information submitted by one of the monitors. In other words: More often than not, the computer doesn’t know it’s allowed to use the mode I want it to use.
This situation meets the somewhat arrogant “I know what’s best, I never fail” attitude often seen by graphics software. There is more than one automatic mechanism for changing the resolution to “what is correct”, so just changing the resolution with xrandr doesn’t cut. The underlying mechanisms seem to change frequently from one version to another, and having them documented is probably too much to ask for. It seems like there are some race conditions taking place between different utilities that have a say on this matter. Possibly the reason for the problem I tried to solve on this post.
For clarity: EDID is a chunk of data that is typically stored on a small flash memory on the monitor. This data is fetched through I2C wires that are part of an DVI / HDMI / VGA connector when the monitor is plugged in. This is how the computer knows not only the commercial name of the monitor, but also what graphics modes it supports and prefers.
I have another post which solves this in a more aggressive way, and also one with a related discussion regarding an newer OLED display.
How cinnamon selects the resolution to use
So — the first question is: How does (my very specific) Cinnamon determine which screen resolution is the “correct” one?
This is a journey into the realm of mystery and uncertainty, but it seems like the rationale is to remember previously connected monitors, along with a separate user-selected graphics mode for each.
So the steps are probably something like:
- Grab the list of allowed resolution modes, as presented by xrandr, for the relevant monitor (through libxrandr?). This is typically the set of modes listed in the monitor’s EDID information, but it’s possible to add modes as well (see below).
- If there’s a user logged in, look up .config/monitors.xml in that user’s home directory. If there’s a match between the monitor’s product identification, apply the selected resolution. This file is changed by Cinnamon’s Display setting utility (among others, I guess), and presents the user’s preferences.
- There’s possibly also a globally default monitor.xml at /etc/gnome-settings-daemon/xrandr/. I don’t have such file, and it’s not clear if it’s in effect had it existed. I haven’t tried this one.
- If there’s no matching (or adequate?) mode setting in monitor.xml (or no user logged in), choose the preferred mode, as pointed at by xrandr.
This way or another, monitors.xml only lists width, height and rate for each graphics mode, without the timing details that are required to run it properly. So if the resolution requested in monitors.xml isn’t listed by xrandr, there is no way to request it, as there is crucial information missing. This isn’t supposed to happen ever, since the utility that sets the user’s preferences isn’t supposed to select a mode that the monitor doesn’t support. But if it does, the logical thing would be to ignore the resolution in monitors.xml, and go on with the monitor’s preferred mode. In reality, it appears like this causes the blank screen that I’ve mentioned on this post.
The automatic setting of resolution seems to take place when some kind of X session starts (the login screen and after the user logs in) as well as when a new monitor is hotplugged. Setting a monitor’s mode with xrandr seems to trigger an automatic setting as well sometimes. Having tried to set the resolution with xrandr a few times, it reverts sometimes to the automatic setting, and sometimes it stays with the one I set. Go figure.
It seems to be related to Cinnamon’s setting daemon (executed as /usr/lib/x86_64-linux-gnu/cinnamon-settings-daemon/csd-xrandr), which, according to this thread, can be turned off by going to Menu > Startup Applications and switch off “Cinnamon Setting Daemon – xrandr” (that simple?!). It has also been suggested to remove ~/.config/autostart/cinnamon-settings-daemon-xrandr.desktop, but I don’t have such file on my computer. Anyhow, I discovered this possibility after solving my own problem in another way, so I didn’t get further into this.
How I got it done (hopefully)
IMPORTANT: I’ve added another post on how to really nail down the graphics mode, even if the trick below fails.
Since there are all kinds of ghosts in the system that insist on “fixing” the display resolution, I might as well play along. So the trick is as follows:
- Edit ~/.config/monitors.xml (manually), setting the resolution for all monitors listed to the one I want.
- Make sure that the desired graphics mode, along with its timing parameters, is listed by xrandr, even if the monitor didn’t mention it in its EDID info.The first step is relatively easy. The entries in the XML file look like this:
<output name="HDMI3">
<vendor>SNY</vendor>
<product>0x0801</product>
<serial>0x01010101</serial>
<width>1360</width>
<height>768</height>
<rate>60</rate>
<x>0</x>
<y>0</y>
<rotation>normal</rotation>
<reflect_x>no</reflect_x>
<reflect_y>no</reflect_y>
<primary>yes</primary>
</output>
This is after editing the file. I needed 1360 x 768 @60 Hz, as shown above. So just set the width, height and rate tags in the XML file for all entries. No matter what monitor the system thinks it sees, the “user preference” is the same.
Now making sure that the mode exists: Add something like the following as /etc/X11/Xsession.d/10add-xrandr-mode (owned by root, not executable, no shebang):
xrandr -d :0 --newmode "hdmi_splitter" 85.5 1360 1424 1536 1792 768 771 777 795 +hsync +vsync xrandr -d :0 --addmode HDMI3 hdmi_splitter xrandr -d :0 --output HDMI3 --mode hdmi_splitter
Needless to say (?), this relates to the specific graphics mode.
So this file is executed every time X is started (and hence the xrandr modes list is cleared). All it does is making sure that the relevant output port (HDMI3) knows how to display 1360 x 768. Note that the name of the mode has no particular significance, and that the frame rate isn’t given explicitly, but is calculated by the tools. I got these figures from an xrandr readout with the desired monitor connected directly. See the full listing at the end of this post. It’s the first entry there.
The third command actually switches the display to the desired mode. It can be removed actually, because it’s overridden very soon anyhow. Nevertheless, it shows the command that can be used manually on console, given the two earlier commands (should not be needed, given that the mode is invoked automatically, fingers crossed).
That’s it. Except for occasional glitches (getting full control of this was too much to expect), the two actions mentioned above are enough to get the mode I wanted. Not the “no matter what” I wanted, but close enough.
As for the -d :0 flags, it’s required in remote sessions and scripts. Alternatively, start with an
$ export DISPLAY=:0
Using cvt to obtain the timing parameters (not!)
It’s suggested on some websites to obtain the timing parameters with something like
$ cvt 1360 768 60 # 1360x768 59.80 Hz (CVT) hsync: 47.72 kHz; pclk: 84.75 MHz Modeline "1360x768_60.00" 84.75 1360 1432 1568 1776 768 771 781 798 -hsync +vsync
I tried this, and the monitor didn’t sync on the signal. It’s indeed a pretty lousy monitor to miss on a DVI signals, and still.
Note the small differences between the timing parameters — that’s probably the reason for this failure. So when the real parameters can be obtained, use them. There is no secret catch-all formula for all graphics modes. The formula works on a good day.
Hands off, Cinnamon’s daemon!
My original idea was to turn off all automatic graphics mode setting mechanisms, and stay with a single xrandr command, running from /etc/X11/Xsession.d/ or something. It was a great idea, but it didn’t work: I saw a momentary switch to the mode I wanted, and then it changed to something else. I could have added some kind of daemon of my own, that waits a bit and then changes the mode with xrandr, but that’s just adding another daemon to wrestle with the others.
So this didn’t really help, but I’ll leave it here anyway, in case someone wants to change the display mode without having some daemon change it back. Note that according to this page, using gsettings as shown below works only up to Cinnamon before version 3.4, after which the procedure is different (haven’t tried it however): Copy /etc/xdg/autostart/cinnamon-settings-daemon-xrandr.desktop to $HOME/.config/autostart. Then append the line Hidden=true to the copied file.
In short, YMMV. Here’s how I did it on my system (and then found it’s not good enough, as mentioned above).
Resolution mode settings made with xrandr will be sporadically overridden by cinnamon-settings-daemon, which has a lot of plugins running for different housekeeping tasks. One of them is to keep X-Window’s display resolution in sync with .config/monitors.xml. So disable it.
Following my own post, this is typically the setting for the said plugin:
$ gsettings list-recursively org.gnome.settings-daemon.plugins.xrandr org.gnome.settings-daemon.plugins.xrandr active true org.gnome.settings-daemon.plugins.xrandr priority 0 org.gnome.settings-daemon.plugins.xrandr default-monitors-setup 'follow-lid' org.gnome.settings-daemon.plugins.xrandr default-configuration-file '/etc/gnome-settings-daemon/xrandr/monitors.xml'
So turn it off:
$ gsettings set org.gnome.settings-daemon.plugins.xrandr active false
and then check again with the list-recursively command above.
xrandr output: The full list of modes
Just for reference, these are the modes given by xrandr for the monitor I did all this for:
$ xrandr -d :0 --verbose
[ ... ]
1360x768 (0x4b) 85.500MHz +HSync +VSync *current +preferred
h: width 1360 start 1424 end 1536 total 1792 skew 0 clock 47.71KHz
v: height 768 start 771 end 777 total 795 clock 60.02Hz
1920x1080i (0x10b) 74.250MHz -HSync -VSync Interlace
h: width 1920 start 2008 end 2052 total 2200 skew 0 clock 33.75KHz
v: height 1080 start 1084 end 1094 total 1125 clock 60.00Hz
1920x1080i (0x10c) 74.250MHz +HSync +VSync Interlace
h: width 1920 start 2008 end 2052 total 2200 skew 0 clock 33.75KHz
v: height 1080 start 1084 end 1094 total 1125 clock 60.00Hz
1920x1080i (0x10d) 74.250MHz +HSync +VSync Interlace
h: width 1920 start 2448 end 2492 total 2640 skew 0 clock 28.12KHz
v: height 1080 start 1084 end 1094 total 1125 clock 50.00Hz
1920x1080i (0x10e) 74.176MHz +HSync +VSync Interlace
h: width 1920 start 2008 end 2052 total 2200 skew 0 clock 33.72KHz
v: height 1080 start 1084 end 1094 total 1125 clock 59.94Hz
1280x720 (0x10f) 74.250MHz -HSync -VSync
h: width 1280 start 1390 end 1430 total 1650 skew 0 clock 45.00KHz
v: height 720 start 725 end 730 total 750 clock 60.00Hz
1280x720 (0x110) 74.250MHz +HSync +VSync
h: width 1280 start 1390 end 1430 total 1650 skew 0 clock 45.00KHz
v: height 720 start 725 end 730 total 750 clock 60.00Hz
1280x720 (0x111) 74.250MHz +HSync +VSync
h: width 1280 start 1720 end 1760 total 1980 skew 0 clock 37.50KHz
v: height 720 start 725 end 730 total 750 clock 50.00Hz
1280x720 (0x112) 74.176MHz +HSync +VSync
h: width 1280 start 1390 end 1430 total 1650 skew 0 clock 44.96KHz
v: height 720 start 725 end 730 total 750 clock 59.94Hz
1024x768 (0x113) 65.000MHz -HSync -VSync
h: width 1024 start 1048 end 1184 total 1344 skew 0 clock 48.36KHz
v: height 768 start 771 end 777 total 806 clock 60.00Hz
800x600 (0x114) 40.000MHz +HSync +VSync
h: width 800 start 840 end 968 total 1056 skew 0 clock 37.88KHz
v: height 600 start 601 end 605 total 628 clock 60.32Hz
720x576 (0x115) 27.000MHz -HSync -VSync
h: width 720 start 732 end 796 total 864 skew 0 clock 31.25KHz
v: height 576 start 581 end 586 total 625 clock 50.00Hz
720x576i (0x116) 13.500MHz -HSync -VSync Interlace
h: width 720 start 732 end 795 total 864 skew 0 clock 15.62KHz
v: height 576 start 580 end 586 total 625 clock 50.00Hz
720x480 (0x117) 27.027MHz -HSync -VSync
h: width 720 start 736 end 798 total 858 skew 0 clock 31.50KHz
v: height 480 start 489 end 495 total 525 clock 60.00Hz
720x480 (0x118) 27.000MHz -HSync -VSync
h: width 720 start 736 end 798 total 858 skew 0 clock 31.47KHz
v: height 480 start 489 end 495 total 525 clock 59.94Hz
720x480i (0x119) 13.514MHz -HSync -VSync Interlace
h: width 720 start 739 end 801 total 858 skew 0 clock 15.75KHz
v: height 480 start 488 end 494 total 525 clock 60.00Hz
720x480i (0x11a) 13.500MHz -HSync -VSync Interlace
h: width 720 start 739 end 801 total 858 skew 0 clock 15.73KHz
v: height 480 start 488 end 494 total 525 clock 59.94Hz
640x480 (0x11b) 25.200MHz -HSync -VSync
h: width 640 start 656 end 752 total 800 skew 0 clock 31.50KHz
v: height 480 start 490 end 492 total 525 clock 60.00Hz
640x480 (0x11c) 25.175MHz -HSync -VSync
h: width 640 start 656 end 752 total 800 skew 0 clock 31.47KHz
v: height 480 start 490 end 492 total 525 clock 59.94Hz
The vast majority are standard VESA modes.