How to enable x11vnc at startup using systemd ?

Question

Hi everyone,
This is what i tried:
copy /usr/lib/systemd/system/x11vnc.service to /etc/systemd/system/x11vnc.service
edit /etc/systemd/system/x11vnc.service, added the Install section and changed ExecStart
[Unit]
Description=VNC Server for X11
Requires=graphical.target
After=graphical.target
[Service]
Type=forking
ExecStart=/usr/bin/x11vnc -rfbauth /etc/x11vnc.pass -rfbport 5900 -display :0 -auth /var/run/lxdm/lxdm-\:0.auth \
-forever -bg -o /var/log/x11vnc.log -xkb -noxrecord -noxfixes -noxdamage -nomodtweak
[Install]
WantedBy=multi-user.target
systemctl daemon-reload
systemctl enable x11vnc
But after reboot, x11vnc was not started automatically, while starting the x11vnc service manually afterwards worked. It turned out I had produced a dependency cycle.
root@archlinux:~# journalctl --this-boot | fgrep cycle
Aug 24 13:09:21 archlinux systemd[1]: Found ordering cycle on graphical.target/start
Aug 24 13:09:21 archlinux systemd[1]: Walked on cycle path to multi-user.target/start
Aug 24 13:09:21 archlinux systemd[1]: Walked on cycle path to x11vnc.service/start
Aug 24 13:09:21 archlinux systemd[1]: Walked on cycle path to graphical.target/start
Aug 24 13:09:21 archlinux systemd[1]: Breaking ordering cycle by deleting job x11vnc.service/start
Aug 24 13:09:21 archlinux systemd[1]: Job x11vnc.service/start deleted to break ordering cycle starting with graphical.target/start
But I am unsure how I can resolve the cycle. Here are the other units envolved in the cycle (both unchanged):
/usr/lib/systemd/system/multi-user.target:
[Unit]
Description=Multi-User System
Documentation=man:systemd.special(7)
Requires=basic.target
Conflicts=rescue.service rescue.target
After=basic.target rescue.service rescue.target
AllowIsolate=yes
[Install]
Alias=default.target
/usr/lib/systemd/system/graphical.target:
Description=Graphical Interface
Documentation=man:systemd.special(7)
Requires=multi-user.target
After=multi-user.target
Conflicts=rescue.target
Wants=display-manager.service
AllowIsolate=yes
[Install]
Alias=default.target
My intention was to start x11vnc.service after graphical.target is reached. How can I achieve this ?
Altering my Install section to
[Install]
Alias=default.target
screws up the system and leads me to an emergency shell at next boot because /etc/systemd/system/default.target was symlinked to /etc/systemd/system/x11vnc.service by systemctl enable x11vnc.
Any ideas / suggestins ?
Thanx
Last edited by Markus.N2 (2013-08-24 16:15:48)

Answer 1

If you are not set completely on using x11vnc but want vnc to run as a server so that you can remotely access a machine even before login, then one way which I used to use regularly is to start the vncserver from the tigervnc package by adding a section to the xorg.conf file. This needs tigervnc to be installed on both local and remote machine.  It is a while since I have used this method but when I did so I used to put something like the following in the xorg.conf file:
Section "Module"
Load "vnc"
EndSection
and later in the file:
Section "Screen"
Identifier "Screen0"
Device "Videocard0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Option "SecurityTypes" "VncAuth"
Option "UserPasswdVerifier" "VncAuth"
Option "passwordFile" "/opt/Local/etc/vnc/passwd"
EndSubSection
EndSection
If you already have an xorg.conf file then you only need to add the load "vnc " and Option  "passwordFile" to the existing xorg.conf. If not, then you can create a minimal xorg.conf to get the vnc module loaded (xorg module not kernel module just to be clear)
Then use the vncpasswd command to create a password file, and have this accessible at /opt/Local/etc/passwd or whathever path and name for the file is suitable for your machine.
Then reboot the computer and the vnc module should be running on the "remote" machine. Check the org log to see if that is the case.
The most secure way to then access the machine remotely is to ssh to the machine from the client in a first terminal window, port forwarding say local port 55900 to the default remote port at 5900 which is the default port on which the vncserver is listening on the remote end.
After making sure you have a copy of the password file on the local client machine that wants access to the remote machine, then in a second terminal window run the usual vnc command "vncviewer --passwd path/to/password-file localhost:55900" to access the remote machine using the local port in this case at 55900 which will tunnel the vnc traffic down the ssh tunnel. 
If this is set up correctly then even from a remote reboot if the remote machine has booted up and has a graphical login screen awaiting the username and password, making the vnc connection as above should allow you to "see" the remote machine screen on the local client, and if the window focus is in this vnc window you should be able to login and use the remote machine in the same way as if you were accessing the remote machine with its mouse and keyboard. If the remote machine is already running a user session then you should see a copy of the remote screen and have mouse and keyboard control remotely.
I ran this technique for some years using different flavours of linux including arch linux but I have not needed to use it for about 9 months now so I have not existing setup with a current arch linux to check that this still works, but I would be surprised if this does not work with arch with up to date packages.
One important note though is that if anyone has the address of the machine and the vnc password file then essentially they can log in and do what they like at the other end within the privileges of the logged in user at the remote machine - so care is needed to ensure that nobody has access to the password file that you would not trust making the connection! Of course also once the vnc server is running at the remote end then the machine is continuously accessible with the above method since it is running without reference to a specific user login.
I hope this helps.
Last edited by mcloaked (2014-06-03 15:21:18)