X11 connection broken when using Qt 5.14

dcoup

I'm working on migrating an application from Qt 5.9 to Qt 5.14. For 64-bit Linux we usually run the application with X11 forwarding enabled so we can use the application from a Windows workstation.

This approach works fine when using the version of the application built with Qt 5.9. But with Qt 5.14, I see a quick flash, like the application is trying to start, and then nothing. An error message says "The X11 connection broke (error 1). Did the X11 server die?". The server hasn't died, but the connection did break. I've seen this with two SSH clients on my workstation. I've tried upgrading the X11 software on the Linux environment, but that hasn't worked. The X11 software on my Windows workstation is Xming 6.9.0.31.

A colleague tried executing the application built with Qt 5.14 using a Linux environment with a direct connected console, and this worked without problems. So something related to X11 seems to be the issue. Have any problems like this been seen with Qt 5.14?

Kent-Dorfman

The public release Xming server doesn't seem to be actively supported and was developed way back int the XP days. I'd suggest that the windoze X server itself is less than stable.

Try it with the cygwin X server before making additional asusmptions.

SGaist

Hi,

Are you starting your application from a terminal ?
If so, you should start it with the QT_DEBUG_PLUGINS environment variable set to 1 to see if there's some information with regard to the xcb plugin.

Kent-Dorfman

The public release Xming server doesn't seem to be actively supported and was developed way back int the XP days. I'd suggest that the windoze X server itself is less than stable.

Try it with the cygwin X server before making additional asusmptions.

dcoup

@SGaist I'm seeing messages like this when that environment variable is set to 1 and Qt 5.14 is used:

Got keys from plugin meta data ("xcb")
loaded library "/home/eday/qt/Qt5.14.1/5.14.1/gcc_64/plugins/platforms/libqxcb.so"
qt.qpa.xcb: X server does not support XInput 2
failed to get the current screen resources

qt.qpa.xcb: QXcbConnection: XCB error: 1 (BadRequest), sequence: 163, resource id: 90, major code: 130 (Unknown), minor code: 47
qt.qpa.xcb: QXcbConnection: XCB error: 170 (Unknown), sequence: 176, resource id: 90, major code: 146 (Unknown), minor code: 20
The X11 connection broke (error 1). Did the X11 server die?

With Qt 5.9 there is much less output, but I see messages like these:

failed to get the current screen resources
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: iCCP: known incorrect sRGB profile
QXcbConnection: XCB error: 170 (Unknown), sequence: 170, resource id: 90, major code: 146 (Unknown), minor code: 20

With Qt 5.9 the application does start.

artwaw

@Kent-Dorfman xming is not outdated, it's just no longer free http://www.straightrunning.com/XmingNotes/ but actively developed. It's just OP using very outdated one.

dcoup

@Kent-Dorfman I tried my test using Cygwin's X server instead of the free Xming software. It worked.

Kent-Dorfman

@artwaw
**
@Kent-Dorfman xming is not outdated, it's just no longer free http://www.straightrunning.com/XmingNotes/ but actively developed. It's just OP using very outdated one.
ed text**

The "free version" the op uses is outdated. hasn't been updated in like 6 or 7 years.