configuring x server on headless server

objective: make nautilus . command work in a headless server.

install nautilus

$ sudo apt install nautilus

I’ve tried installing a display manager, but instead I succeeded with directly starting the x server with xinit. related link

install xinit

$ sudo apt install xinit

create new xorg.conf

if it is a headless server, then the default xorg confs(located at /usr/share/X11/xorg.conf.d) is not going to work because it doesn't have a real physical screen.

To be specific, I’ve tried launching the X server with lightdm.

$ sudo systemctl start lightdm

However, this does not work. We can see why it doesn’t work inside the xorg log file located in /var/log/Xorg.0.log

This log file loggs the procedure of launching Xorg. If the conf file is wrong, it will say that parsing conf file cause the error. If an error occured due to no screens, it will be said so inside this file. So it is important to keep checking this log file whenever X server does not seem to start properly.

Since the default confs do not work, we need to create a new one. reference link

$ sudo Xorg :0 -configure

a file named xorg.conf.new will be created in your current location.

If you have multiple GPU, then the very first section which defines ServerLayout will have multiple screens like below

Section "ServerLayout"
    Identifier     "X.org Configured"
    Screen      0  "Screen0" 0 0
    Screen      1  "Screen1" RightOf "Screen0"
    Screen      2  "Screen2" RightOf "Screen1"
    Screen      3  "Screen3" RightOf "Screen2"
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

The default setting will create a screen for each GPU and will attach them along side-by-side. But since this configuration will be using precious GPU resources, we can reduce to using just one. Remove all screen definition blocks except screen0. So this section will look like:

Section "ServerLayout"
    Identifier     "X.org Configured"
    Screen      0  "Screen0" 0 0
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"
EndSection

Since we use only Screen0, delete all sections for Screen1-3. If you don't delete them it will cause an error when parsing.

Section "Screen"
    Identifier "Screen0"
    Device     "Card0"
    Monitor    "Monitor0"
    SubSection "Display"
        Viewport   0 0
        Depth     1
    EndSubSection

Looking at the Screen0 section, we notice that it uses the device named Card0. Checking out the Card0 section,

Section "Device"
    Identifier  "Card0"
    Driver      "nvidia"
    BusID       "PCI:5:0:0"
EndSection

we can see that this is directing to one of the nvidia GPU cards.

+-----------------------------------------------------------------------------+
| NVIDIA-SMI 384.81                 Driver Version: 384.81                    |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  TITAN Xp            Off  | 00000000:05:00.0 Off |                  N/A |
| 23%   26C    P8     7W / 250W |  11645MiB / 12188MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
|   1  TITAN Xp            Off  | 00000000:06:00.0 Off |                  N/A |
| 23%   26C    P8     8W / 250W |  11602MiB / 12189MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
|   2  TITAN Xp            Off  | 00000000:09:00.0 Off |                  N/A |
| 23%   24C    P8     8W / 250W |  11604MiB / 12189MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
|   3  TITAN Xp            Off  | 00000000:0A:00.0 Off |                  N/A |
| 23%   26C    P8     8W / 250W |  11602MiB / 12189MiB |      0%      Default |
+-------------------------------+----------------------+----------------------+
​

Cross-referencing with nvidia-smi, we can see that Card0 is pointing to the first GPU in the list. (it has Bus-Id value of 00000000:05:00.0 which matches the value in the BusId value of Card0 section)

Also in order to ignore the fact that there is no physical screen attached to the server, we add the AllowEmptyInitialConfiguration option inside the Card0 section.(reflink1 , reflink2)

It should look like:

Section "Device"
    Identifier  "Card0"
    Driver      "nvidia"
    BusID       "PCI:5:0:0"
    Option "AllowEmptyInitialConfiguration"
EndSection

BTW, AllowEmptyInitialConfiguration option may not work with old nvidia GPU cards, according to reflink2. But I haven't tested if this is true or not, so just keep this in notice.

Another option needs to be added to the Monitor0 section. (reflink)

Please add the IgnoreEDID option. It should look like this:

Section "Monitor"
    Identifier   "Monitor0"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
    Option   "IgnoreEDID"
EndSection

We have finished modifying the new configuration file. Copy or move this file to /etc/X11

$ sudo mv xorg.conf.new /etc/X11/xorg.conf

By renaming it to xorg.conf under /etc/X11 directory, this file will be used as the default configuration file.

Now try starting the X server

$ sudo xinit

If successful, it will not show any errors and it will keep running. The terminal will not be returned to the user since the xinit is still occupying it.

You can cross-check that X server is running well with ps.

$ ps -e | grep x
  214 ?        00:00:00 ixgbe
  407 ?        00:00:00 ext4-rsv-conver
  898 ?        00:00:00 ext4-rsv-conver
  909 ?        00:00:00 ext4-rsv-conver
 1121 ?        00:00:14 lxcfs
21439 ?        00:00:00 xfsalloc
21440 ?        00:00:00 xfs_mru_cache
27182 ?        00:00:00 xinit  <---HERE IT IS!
27198 ?        00:00:00 xterm

Now we are sure that x server works, we need to run this in the background. Cancel the process that we launched above, and rerun it in the background.

$ sudo xinit &

make sure that X11 Forwarding is enabled

Even after configuring all of this, I faced an error when executing nautilus

$ nautilus .
Gtk-WARNING **: cannot open display:

In this case, there is a high possibility that your ssh connection did not have X11 Forwarding enabled. Kill you current ssh connection, ensure X11 Forwarding is enabled, and reconnect to the server.

For me, this solved the problem.