Black screen when logging into desktop

Question

On Kubuntu 15.10 I receive a black screen when logging in via the Display Manager. I can use Ctrl-Alt-F6 to log into a text console and see my files, but even in that environment when I type startx the screen just goes blank and nothing further happens. I have renamed my ~/.kde directory to ~/.kde-old but the problem still persists.

The display manager has a setting "failsafe", when I try to log in with it set I just get booted back to the display manager screen again after a few seconds.

Here is dmesg, I've pasted what I think are the relevant lines below but clicking on the link will bring you to Pastebin where the entire log is stored.

[  117.572448] kscreen_backend[1626]: segfault at 10 ip 00007f8c0cf068c0 sp 00007ffdfd0ed358 error 4 in KSC_XRandR.so[7f8c0cef3000+20000]
[  118.556865] kactivitymanage[1610]: segfault at 18 ip 00007fdc57430ee0 sp 00007ffde65b6878 error 4 in libqxcb.so[7fdc57402000+b5000]
[  118.569140] krunner[1633]: segfault at 18 ip 00007fcd52973e38 sp 00007ffed1ec3370 error 4 in libqxcb.so[7fcd5292a000+b5000]
[  118.572032] kdeconnectd[1632]: segfault at 18 ip 00007fcb022f3e38 sp 00007ffc58549500 error 4 in libqxcb.so[7fcb022aa000+b5000]
[  118.578476] kscreen_backend[1639]: segfault at 18 ip 00007f0956e02e38 sp 00007ffc3a121980 error 4 in libqxcb.so[7f0956db9000+b5000]
[  118.578622] kwin_x11[1629]: segfault at 18 ip 00007f2f5d039e38 sp 00007ffcf6c160e0 error 4 in libqxcb.so[7f2f5cff0000+b5000]
[  118.998290] plasmashell[1655]: segfault at 18 ip 00007f39a8edae38 sp 00007ffcf531f110 error 4 in libqxcb.so[7f39a8e91000+b5000]
[  120.469171] kglobalaccel5[1685]: segfault at 18 ip 00007fc6917f1e38 sp 00007fffb2965630 error 4 in libqxcb.so[7fc6917a8000+b5000]
[  120.475815] kglobalaccel5[1687]: segfault at 18 ip 00007f7b14409e38 sp 00007ffe5d3a59f0 error 4 in libqxcb.so[7f7b143c0000+b5000]
[  120.735669] kglobalaccel5[1700]: segfault at 18 ip 00007fde7578ae38 sp 00007ffe9d3d7520 error 4 in libqxcb.so[7fde75741000+b5000]
[  124.165384] show_signal_msg: 2 callbacks suppressed
[  124.165389] korgac[1719]: segfault at 18 ip 00007f4e33530e38 sp 00007ffe1e69b010 error 4 in libqxcb.so[7f4e334e7000+b5000]
[  124.203178] IPv6: ADDRCONF(NETDEV_UP): wlp5s0b1: link is not ready
[  124.821375] wlp5s0b1: authenticate with b0:48:7a:fd:99:ae
[  124.823047] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 1/3)
[  125.023234] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 2/3)
[  125.227080] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 3/3)
[  125.431014] wlp5s0b1: authentication with b0:48:7a:fd:99:ae timed out
[  125.627814] korgac[1727]: segfault at 18 ip 00007f0294472e38 sp 00007ffeec678ea0 error 4 in libqxcb.so[7f0294429000+b5000]
[  127.951872] klauncher[1774]: segfault at 18 ip 00007f25f91b2e38 sp 00007fffc3569a90 error 4 in libqxcb.so[7f25f9169000+b5000]
[  136.059194] wlp5s0b1: authenticate with b0:48:7a:fd:99:ae
[  136.059317] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 1/3)
[  136.261035] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 2/3)
[  136.464894] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 3/3)
[  136.668804] wlp5s0b1: authentication with b0:48:7a:fd:99:ae timed out
[  149.191322] IPv6: ADDRCONF(NETDEV_UP): wlp5s0b1: link is not ready
[  149.816413] wlp5s0b1: authenticate with b0:48:7a:fd:99:ae
[  149.816517] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 1/3)
[  150.017451] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 2/3)
[  150.221322] wlp5s0b1: direct probe to b0:48:7a:fd:99:ae (try 3/3)
[  150.425210] wlp5s0b1: authentication with b0:48:7a:fd:99:ae timed out
[  152.779659] kscreen_backend[1965]: segfault at 10 ip 00007f253f78c8c0 sp 00007ffe7a87d1b8 error 4 in KSC_XRandR.so[7f253f779000+20000]
[  152.941924] kactivitymanage[1952]: segfault at 18 ip 00007f1ae218bee0 sp 00007ffe18581458 error 4 in libqxcb.so[7f1ae215d000+b5000]
[  152.973211] kscreen_backend[1976]: segfault at 18 ip 00007f6ec2cf9e38 sp 00007ffe34ea0320 error 4 in libqxcb.so[7f6ec2cb0000+b5000]
[  152.997937] ksmserver[1975]: segfault at 18 ip 00007f756b05de38 sp 00007fffb2c7fe80 error 4 in libqxcb.so[7f756b014000+b5000]

I was unable to find where xrandr stores it's configuration and the X log doesn't seem to have anything amiss. How should I troubleshoot from here, short of nuking ~ or even /?

Note that this Kubuntu version uses Plasma 5, so I did a new install and not an upgrade from the previous version. The install went well, I've been using the system without any related problems for over a week now. This is a laptop computer that sometimes is connected to an external monitor.

EDIT: I just created a new user test, which also gets booted out of the supposed fail safe login mode. However, this user can log into its desktop just fine. Therefore the problem seems to be in a config file of my user. I'm currently bisecting them now, but I'm still open to ideas. Thank you.

Answer 1

The problem seems to have been in one of the files in ~/.local/share/kscreen. The laptop was connected to an external monitor when it was suspended, but without a monitor when the case was opened. I must stress that I've done this quite a few times already on this setup, so I don't know why things broke this specific time. Here are the files in question, for future reference (yes, I'll probably be the one looking at this six months from now when I have the same issue again):

$ pwd
/home/dotancohen/.local/share/kscreen

$ ls
57aa46c23fd36deda7a9cfb885d7ecee  57aa46c23fd36deda7a9cfb885d7ecee_lidOpened  62f30f6a728bde980d325725a3f19f77

$ cat 57aa46c23fd36deda7a9cfb885d7ecee
[
    {
        "enabled": true,
        "id": "9dda8f0b1446d1e151e4d85bb529df5d",
        "metadata": {
            "fullname": "xrandr-unknown",
            "name": "LVDS1"
        },
        "mode": {
            "refresh": 60.001659393310547,
            "size": {
                "height": 768,
                "width": 1366
            }
        },
        "pos": {
            "x": 1080,
            "y": 464
        },
        "primary": true,
        "rotation": 1
    }
]

$ cat 57aa46c23fd36deda7a9cfb885d7ecee_lidOpened 
[
    {
        "enabled": true,
        "id": "9dda8f0b1446d1e151e4d85bb529df5d",
        "metadata": {
            "fullname": "xrandr-unknown",
            "name": "LVDS1"
        },
        "mode": {
            "refresh": 60.001659393310547,
            "size": {
                "height": 768,
                "width": 1366
            }
        },
        "pos": {
            "x": 1080,
            "y": 464
        },
        "primary": true,
        "rotation": 1
    }
]

$ cat 62f30f6a728bde980d325725a3f19f77 
[
    {
        "enabled": true,
        "id": "9dda8f0b1446d1e151e4d85bb529df5d",
        "metadata": {
            "fullname": "xrandr-unknown",
            "name": "LVDS1"
        },
        "mode": {
            "refresh": 60.001659393310547,
            "size": {
                "height": 768,
                "width": 1366
            }
        },
        "pos": {
            "x": 1080,
            "y": 464
        },
        "primary": true,
        "rotation": 1
    },
    {
        "enabled": true,
        "id": "0ffbea62a50d7b3aa8d01f0a7a422554",
        "metadata": {
            "fullname": "xrandr-E2342-211NDTC7A529",
            "name": "VGA1"
        },
        "mode": {
            "refresh": 60,
            "size": {
                "height": 1080,
                "width": 1920
            }
        },
        "pos": {
            "x": 0,
            "y": 0
        },
        "primary": false,
        "rotation": 2
    }
]

Dotan, just run this and be done with it:

$ rm -rf ~/.local/share/kscreen

And kisses to Meirav, Maayan, Ofek, and Ety while you're at it!