Unfortunately it gives a very strange response:

Progress i suppose.

remove the -- ?

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Wow! Thank you! That worked! :-)
Can you explain to me your code?

Anytime.

It was Shadow_7 that suggested it. I just followed the errors until it worked.

But essentially, it calls out the program, says to use display ':1', and puts it into the background with &.

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Thank you very much! Made my day! :-)

The problem is that vncserver requires local access to a virtual console. logging in over ssh doesn't give you that.

To get around that you might try the solution in:
http://www.cl.cam.ac.uk/research/dtg...nc/sshvnc.html

Doesn't mean it will work for you, but you have to forward the vnc protocol to something to interpret it... a vnc server. (I think I got that right, the page includes a "vncvewer" in some of its operation)

The solution from szboardstretcher works over ssh though. Even www-data can execute that shell script successfully now. So my problem is solved.

The -- tells the shell to stop interpreting past that --. Which would put the '' in question. The '' is basically dropped by the shell before it gets to vncserver when it is interpreted.

vncserver -- :1 &

should also work (in theory).

When everything past that -- isn't interpreted, where's the point to write something past it then? Don't understand unfortunately.

Both versions don't work fot me by the way. It says "Unrecognized option: --".

When things fail it's normally logged somewhere with some details that might hint as to WHY it's failing. YMMV

$ dmesg
$ journalctl -a
# less /var/log/syslog
# egrep -r -i vncserver /var/log/*
$ egrep -r -i vncserver ~/\.*

It's a shell thing. The shell tends to interpret the parameters BEFORE it passes the parameters. Doubly odd since the -- should have been stripped off by the shell, aka interpreted and not passed. Which implies that $(vncserver -- :1) isn't being run in a "shell script". Did you leave out the shebang? #!/bin/bash. Not that it matters, if it doesn't work leaving it out would be the saner thing to do.

I should probably test things, but I don't use vncserver. At least not in the past ten years. X2go, ssh with X forwarding and other routes to do roughly the same thing these days. Not that I've used any of those either. But I do like dividing my screen real-estate up with Xephyr to stack it vertically with Xdmx, so I can fit hundreds of lines of code on screen without needing multiple screens. Or fit the entire output of top on screen in our bloated systemd world.

The shell always interprets the entire line.

the "--" is evaluated as well as anything following it, then all of the results are passed to the application.

How the "--" is handled by the application is up to the application itself. It is USUALLY used to indicate parameters that are to be passed to yet another application, an not used by the base application. This is why the "startx" application uses it. The parameters following the "--" are passed to the X server.

The -- doesn't seem to get interpreted by the shell. There's no difference if I put "#!/bin/bash" on the first line of the shell script or not. The -- is always being passed with the rest of the command. It always results in "Unrecognized option: --".

Tried all of those. Unfortunately didn't find any useful information.