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Old 05-20-2020, 06:49 AM   #1
selfprogrammed
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Registered: Jan 2010
Location: Minnesota, USA
Distribution: Slackware 13.37, 14.2
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Qt5 package failure, what is an xcb and where do I get one.


Most packages have worked fine. Thanks to AlienBob for the pre-compiled packages for slack-14.2.
It is rare that I can compile a package myself without having to spend a couple days fixing bugs in their code.

This started with the newer VLC package, which required Qt5.
I have been without VLC for months now trying to figure out what failed in the package installation.
VLC just quits without ever showing a screen. Starting VLC from console, I can get help, but no display.

I had installed the qt5 from alien.
qt5-5.7.0-i586-3alien

Tried to compile another Qt5 program to test the Qt5 and that failed too.
Unknown QT: phonon4qt5
Where that phonon4qt5 is coming from, I have yet to figure out.
I have phonon-4.8.3 installed.

Finally found a test for qt5. It has some bin in its lib.
The /usr/lib/qt5/bin/pixeltool looked to be a good test for qt5.
It fails, with the message:
Quote:
This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, xcb.

Reinstalling the application may fix this problem.
Running the qt4 pixeltool, /usr/lib/qt/bin/pixeltool, does work.


There has got to be more about the requirements for the qt5 package, than what I know about.
I have upgraded just about every slack package.
The 'xcb' sounds suspiciously like something X11.

Also: Is this qt5 package a devel package (for compiling qt5)?
Does it have to be installed on a separate computer to keep it from killing qt4 projects?

It does not seem to have the same directories in /usr/lib/qt5 that the qt4 does.
I seem to have qt4 qmake around still, but cannot find the qt4 include files in /usr/include.

I have gathered package sources together so I can compile qt5 myself, which will likely fail
(because such large packages always fail to compile first time). So many dependencies, and
rarely any way to tell if they are critical, or optional. I don't know if this would
produce a qt5 better tailored to what I got, or would just be a week wasted.

Last edited by selfprogrammed; 05-21-2020 at 01:14 AM.
 
Old 05-20-2020, 07:00 AM   #2
Alien Bob
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Registered: Sep 2005
Location: Eindhoven, The Netherlands
Distribution: Slackware
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Quote:
Originally Posted by selfprogrammed View Post
This is a question for AlienBob, who can sometime be found in forum.

Most packages from Alien, have worked fine.
This started with the newer VLC package (alien), which required Qt5.
I have been without VLC for months now trying to figure out what failed in the package installation.
VLC just quits without ever showing a screen. Starting VLC from console, I can get help, but no display.

I had installed the qt5 from alien.
qt5-5.7.0-i586-3alien
This is exactly the reason why I am going to remove my ktown repository containing the packages for Slackware 14.2.
The fact that you are posting your question here, means that you are not aware of the fact that I discuss all my packages on my blog and not here in the forum. Another topic here on the LQ forum suggested to people that they should switch to my Plasma5 for Slackware 14.2 (the package "qt5-5.7.0-i586-3alien" comes from that repository). These packages are outdated, they do not get maintenance, and therefore will disappear soon.

If you upgrade to the qt5 package in my regular repository, http://www.slackware.com/~alien/slackbuilds/qt5/ then your VLC problem should go away. Watch out for the dependencies which you probably are also missing and which you can download from my repository as well: OpenAL, SDL_sound, libinput, libxkbcommon.
 
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Old 05-21-2020, 01:44 AM   #3
selfprogrammed
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Registered: Jan 2010
Location: Minnesota, USA
Distribution: Slackware 13.37, 14.2
Posts: 392

Original Poster
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I did not know that:
1. That you have a blog to discuss your packages.
2. There was more than one repository of Alien packages.
Thank you for that information.

History does not go back far enough to track where the download was from.
I do not recognize the slackbook, ktown, nor the plasma tag on that site name. I would not normally download from a site that had a strange name like that.

Because I cannot tell which packages might have been downloaded from that site, I will probably have to track down every Alien package on my repository drives (200 packages maybe)
and decide what to do with them. I doubt there will be any easy way to identify if a package was for this "plasma" thing.

I cannot just always use the latest, sometimes I have to revert to what works. Some newer packages can make unfounded assumptions that "everyone has X" and thus are incompatible.


Checking my bookmarks, I found the link:
http://www.slackware.com/~alien/slackbuilds/
which does look to be the same as the one you posted.

I have in my recent downloads.
qt5-5.9.6-i586-1alien
vlc-2.2.6-i486-1alien
vlc-3.0.8-i586-1alien
vlc-3.0.8_alien_slackbuilds_vlc_build_sources.htm
vlc-3.0.10-i586-1alien

I have not yet found out anything about what new features they may have, new assumptions they may make, or what problems they may pose, except that vlc-3.xx needs qt5.



Thank You.

Last edited by selfprogrammed; 05-21-2020 at 02:46 AM.
 
Old 05-21-2020, 02:11 AM   #4
selfprogrammed
Member
 
Registered: Jan 2010
Location: Minnesota, USA
Distribution: Slackware 13.37, 14.2
Posts: 392

Original Poster
Rep: Reputation: 82
I am left with the question: What the heck is an xcb and why am I missing it.
This post does not ask that as a question.

What I expect is that if I download another package, it also will discover that I do not have this xcb thing.
We know that qt5 and these packages must have worked for "other people", who apparently had an xcb.

It seems that qt4 either has one, or did not need one.

What I do not know is why qt5 did not use linuxfb, or minimal.
What is qt5 expecting from me to get it to use one of those.
Is there some tool that configures qt5, that I have missed even after days of researching the thing.

Also, due to having qt4 projects, it seems that the existence of qt5 on the same system is hostile
to compiling the qt4 projects.
I seem to need a way to figure out a qt5 free compiling environment.
 
Old 05-21-2020, 02:57 AM   #5
ponce
LQ Guru
 
Registered: Aug 2004
Location: Pisa, Italy
Distribution: Slackware
Posts: 5,394

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Quote:
Originally Posted by selfprogrammed View Post
I am left with the question: What the heck is an xcb and why am I missing it.
Eric already answered about this issue above
Quote:
Originally Posted by Alien Bob View Post
If you upgrade to the qt5 package in my regular repository, http://www.slackware.com/~alien/slackbuilds/qt5/ then your VLC problem should go away. Watch out for the dependencies which you probably are also missing and which you can download from my repository as well: OpenAL, SDL_sound, libinput, libxkbcommon.
 
Old 05-21-2020, 04:44 AM   #6
Alien Bob
Slackware Contributor
 
Registered: Sep 2005
Location: Eindhoven, The Netherlands
Distribution: Slackware
Posts: 8,012

Rep: Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743Reputation: 6743
Quote:
Originally Posted by selfprogrammed View Post
I am left with the question: What the heck is an xcb and why am I missing it.
This post does not ask that as a question.

What I expect is that if I download another package, it also will discover that I do not have this xcb thing.
We know that qt5 and these packages must have worked for "other people", who apparently had an xcb.

It seems that qt4 either has one, or did not need one.

What I do not know is why qt5 did not use linuxfb, or minimal.
What is qt5 expecting from me to get it to use one of those.
Is there some tool that configures qt5, that I have missed even after days of researching the thing.
You already stated that you do not have a full installation and like to hand-pick the packages you think you need. That of course, is the core issue, not the fact that you do not understand packages and their interdependencies. Either you learn how all of this works under the hood, or you will now do a full installation of Slackware.
Also, having 200+ packages with an 'alien' tag, but not knowing where they are from or what their relevance is... that is a dangerous form of carelessness.

Quote:
Also, due to having qt4 projects, it seems that the existence of qt5 on the same system is hostile
to compiling the qt4 projects.
I seem to need a way to figure out a qt5 free compiling environment.
Both Qt4 and At5 can co-exist and you can keep compiling for both. It's just a matter of changing or setting environment variables (like QTDIR, QT5DIR etc). You are 'selfprogrammed' so you will figure it out. Read a few of my scripts for instance.
 
Old 05-21-2020, 09:24 AM   #7
selfprogrammed
Member
 
Registered: Jan 2010
Location: Minnesota, USA
Distribution: Slackware 13.37, 14.2
Posts: 392

Original Poster
Rep: Reputation: 82
I see, insult replies. I like to control and manage my own computer, I need information to do that and make my own choices, and that does not agree with you.

Yea, I thought having -Alien in the package name meant that I knew where it came from. My storage scheme was inadequate to cope with the same package naming also being used for something incompatible.

By time I got back here, I had determined the following (this is for any readers who may have a similar problem and need answers).

Why am I missing the "xcb"?
Actually I found that I have the xcb, and it is in /usr/lib/plugins/platforms.
The problem is that qt5 cannot load it.
Exploration of that issue reveals that qt5 dumps this message for many different situations.
There are several solutions, depending on exactly what the problem qt5 is having.
In short, the error message is not informative.

export QT_PLUGIN_DEBUG
This did not tell me anything new.

strace:
Reveals that qt5 is looking at the correct location for xcb, but cannot load it.
It finally turns out, that finding xcb is not the same as loading it.

The problem really was libinput.
Also, libxkbcommon can give the same problem, but in my case fixing
libinput made the difference. There seems to be a dependency from xcb
to libxkbcommon, so loading of xcb fails if it cannot load libxkbcommon.
However, qt5 reports xcb and nothing else.
Don't know of a dependency from xcb to libinput, but that is how it is.

I compiled my own libinput from my own build script, removed the need for the wacom package, added my own customizations.
Removed the alien package, installed mine, and now pixeltool-qt5 works.
qt5 has made a window !! Impressive accomplishment for a whole nights work.

But, VLC still would not work. It still crashes with the same message.


So, decided to change out the qt5 package.
The qt5-5.7.0 was not actually declared to be buggy, but was from the "wrong" repository so something mysterious might be wrong with it.
Otherwise, there is no expectation that thrashing the packages is going to change anything.
But, qt5-5.9.6 was already downloaded and sitting there, so swapped them to see if it actually made
any difference.

( It has been my experience that when you have a mysterious conflict problem, that it is best to understand what problem you have and not to change the installations around too much before you figure it out.
There is a risk that you will have to walk all your changes back, undo it all, so you better remember what it was you did.
Just thrashing the packages to see what happens is not a good debugging method.
I have had to clean the site down a clean directory several times to undo the kind of damage that repeatedly changing installation packages can do.
Now, if you can get information that the current package is buggy in a way relevant to your problem, then changing it is the best course to take.
This has nothing to do with upgrading to a new version, which is entirely different when it is done in an installation that is known to be working. )

VLC will bring up a display window now.
VLC still does not work, as it has other problems now
but I got the display window.

(Yea, Alien said so. I really get little information from his posts. Being told "DO THIS" is not information, and I already know he wants to configure my machine to suit himself.
I still don't know if he knew something or not. )

I still wonder if compiling my own qt5 would improve things. Depends upon how much customizable configuration there is in it.
I expect it may be more rewarding to compile a customized VLC. Get some better control over the thing.
At least I will know more of what issues there are, and there are probably some things that could be cut out as it.

Last edited by selfprogrammed; 05-21-2020 at 11:07 AM.
 
Old 05-21-2020, 10:37 AM   #8
bassmadrigal
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Location: West Jordan, UT, USA
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Quote:
Originally Posted by selfprogrammed View Post
I see, insult replies. I like to control and manage my own computer, I need information to do that and make my own choices, and that does not agree with you.
The problem is the "information" isn't available on what's needed for partial installs since Slackware doesn't provide that info. Alien does provide the needed info for his packages by providing the required dependencies. He doesn't need to provide why each dependency is needed. You don't have to use his packages (nor is he asking you to), so if you choose to use them, you're choosing to abide by how he provides them.

If you don't like how he provides them, stop using them and either use someone else's or build your own.

Quote:
Originally Posted by selfprogrammed View Post
Yea, I thought having -Alien in the package name meant that I knew where it came from.
You do know it came from him (well, if you downloaded it from his site or one of the mirrors), but he uses the same tag for all his packages, so it might be from different repos he provides.

Quote:
Originally Posted by selfprogrammed View Post
Why am I missing the "xcb"?
Because you didn't install the required libxcbcommon package that is a required dependency, or if you did install it, it is missing its own dependencies or it is not the right version (since qt5 would be compiled against a specific version and any major updates to libxcbcommon can break that).

Quote:
Originally Posted by selfprogrammed View Post
Just thrashing the packages to see what happens is not a good debugging method.
Blindly installing packages to try and fix a problem is usually not a good idea, but if you're running vastly out-of-date packages and aren't sure if they're designed to work together, installing up-to-date qt5 and the required dependencies is the first debug method you should attempt!

Quote:
Originally Posted by selfprogrammed View Post
I have had to clean the site down a clean directory several times to undo the kind of damage that repeatedly changing installation packages can do.
There might be a few leftover files or directories, but certainly nothing disastrous is left on the system (unless you're using some crazy packages).

Quote:
Originally Posted by selfprogrammed View Post
(Yea, Alien said so. I really get little information from his posts. Being told "DO THIS" is not information, and I already know he wants to configure my machine to suit himself.
He's telling you what a full Slackware install needs to run vlc. If you don't want to follow his instructions, then you need to figure it out on your own. He is not under any obligation to support partial Slackware installs or trying to run his packages without installing the required dependencies.

Quote:
Originally Posted by selfprogrammed View Post
I still wonder if compiling my own qt5 would improve things. Depends upon how much customizable configuration there is in it.
qt5 is a very difficult program to compile. Even on high-end machines, it can still take hours. On lower end machines, you can be looking at days. But there are several methods to compile qt5, including several SlackBuilds, so go for it.

Quote:
Originally Posted by selfprogrammed View Post
I expect it may be more rewarding to compile a customized VLC. Get some better control over the thing.
At least I will know more of what issues there are, and there are probably some things that could be cut out as it.
Alien's VLC is very full-featured. There is a lot of fluff you could excise from it if you want to take the time to do so. Whether that will be beneficial depends on the usage and the person, I suppose.
 
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