Xpra: Ticket #1455: xpra does not check for MIT-SHM - server logfile with MBs of error messages

If xpra server uses a display without extension MIT-SHM, the server log file gets filled with repeating error messages and can increase to a size of some MB within minutes.

Example: 2017-03-01 16:12:16,470 XShmWrapper.setup() XShmAttach(..) failed! Xlib: extension "MIT-SHM" missing on display ":500". Xlib: extension "MIT-SHM" missing on display ":500".

This can lead to an overfilled hard disk after some hours. xpra should check whether MIT-SHM is available and avoid to use it if it is missing.

Wed, 01 Mar 2017 15:46:08 GMT - Antoine Martin: owner changed; milestone set

owner changed from Antoine Martin to mviereck
milestone set to 2.1

Done in r15198. Please close if this works for you. (this may be applied to the v1.0.x LTS branch at some point)

Tested by adding -extension MIT-SHM to my xvfb command line.

FYI: you can also use this environment switch with older versions:

XPRA_XSHM=0 xpra start ..

Note: beware, the non-xshm codepath is not very well tested.

Sat, 11 Mar 2017 13:18:52 GMT - mviereck: status changed; resolution set

status changed from new to closed
resolution set to fixed

Much thanks for your hint with environment variable XPRA_XSHM! That does help me a lot, as I need to be compatible with older xpra versions. Now I set XPRA_XSHM whenever I connect to an X server without MIT-SHM and leave it away if X supports it. I still did not test your bug fix, sorry, as I was a bit confused how to get and compile r15198. So far, I did not encounter any problems with xpra and MIT-SHM disabled. I also did not have any problems before except the growing logfile.

Sun, 12 Mar 2017 08:52:12 GMT - Antoine Martin:

That does help me a lot, as I need to be compatible with older xpra versions.

FYI: the currently supported version (1.0 LTS) is compatible with older xpra versions going as far back as the previous LTS version (0.14.x), see wiki/Versions for details. (using anything else means version with lots of known bugs, including security issues..)

Sun, 12 Mar 2017 10:51:22 GMT - Antoine Martin: milestone changed

milestone changed from 2.1 to 2.0

Sun, 01 Oct 2017 16:52:19 GMT - mviereck:

I found one case where disabling MIT-SHM causes an error. Having a custom X server without MIT-SHM, and starting xpra server with XPRA_XSHM=0 xpra shadow $DISPLAY --use-display, I get an empty black window with xpra attach and repeating server error messages:

2017-10-01 18:45:10,826 client 1: Attached to :101 (press Control-C to detach)
2017-10-01 18:45:11,064 Warning: failed to capture pixels of window 0x25c:
2017-10-01 18:45:11,065  unbound method get_image() must be called with GTKRootWindowModel instance as first argument (got XImageCapture instance instead)

With MIT-SHM enabled, everything works fine. xpra v2.1.2-r16903 on debian stretch (Not really an issue for me as I don't need this setup, just want to report.)

Mon, 02 Oct 2017 05:21:39 GMT - Antoine Martin:

Fixed in r17019 (will backport).

Related improvements:

r17018: log warning if xshm not available
r17020: use correct bytes-per-pixel

Sat, 23 Jan 2021 05:24:46 GMT - migration script:

this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1455