Random screen locking happens about once an hour. Mouse is not responding, keyboard is, but GUI does not respond. To overcome the problem I have to switch to terminal with ctrl+alt+1 and go back. In dmesg I can see:
[ 68.509976] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510021] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510044] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510064] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510083] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510102] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510134] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510154] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.510644] ACPI Warning: \_SB_.PCI0.RP05.PEGP._DSM: Argument #4 type mismatch - Found [Buffer], ACPI requires [Package] (20140424/nsarguments-95)
[ 68.615945] vgaarb: this pci device is not a vga device
$ dmesg | grep vgaarb
[ 0.524324] vgaarb: setting as boot device: PCI:0000:00:02.0
[ 0.524325] vgaarb: device added: PCI:0000:00:02.0,decodes=io+mem,owns=io+mem,locks=none
[ 0.524328] vgaarb: loaded
[ 0.524329] vgaarb: bridge control possible 0000:00:02.0
[ 1.498735] vgaarb: device changed decodes: PCI:0000:00:02.0,olddecodes=io+mem,decodes=io+mem:owns=io+mem
[ 5.667900] vgaarb: this pci device is not a vga device
[ 6.409112] vgaarb: this pci device is not a vga device
[ 68.506178] vgaarb: this pci device is not a vga device
[ 68.615945] vgaarb: this pci device is not a vga device
---
ApportVersion: 2.14.1-0ubuntu3.11
Architecture: amd64
AudioDevicesInUse:
USER PID ACCESS COMMAND
/dev/snd/pcmC1D0p: tm 2422 F...m pulseaudio
/dev/snd/controlC0: tm 2422 F.... pulseaudio
/dev/snd/controlC1: tm 2422 F.... pulseaudio
CurrentDesktop: Unity
DistroRelease: Ubuntu 14.04
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-05-28 (4 days ago)
InstallationMedia: Ubuntu 14.04.2 LTS "Trusty Tahr" - Release amd64 (20150218.1)
MachineType: Dell Inc. Latitude E5540
NonfreeKernelModules: nvidia
Package: linux (not installed)
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.16.0-38-generic root=UUID=9a540be9-ff2e-45f9-8fa9-84e7ee420e26 ro quiet splash
ProcVersionSignature: Ubuntu 3.16.0-38.52~14.04.1-generic 3.16.7-ckt10
RelatedPackageVersions:
linux-restricted-modules-3.16.0-38-generic N/A
linux-backports-modules-3.16.0-38-generic N/A
linux-firmware 1.127.12
Tags: trusty
Uname: Linux 3.16.0-38-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm cdrom dip lpadmin plugdev sambashare sudo
_MarkForUpload: True
dmi.bios.date: 02/02/2015
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A11
dmi.board.name: 0GW97C
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 9
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvrA11:bd02/02/2015:svnDellInc.:pnLatitudeE5540:pvr01:rvnDellInc.:rn0GW97C:rvrA00:cvnDellInc.:ct9:cvr:
dmi.product.name: Latitude E5540
dmi.product.version: 01
dmi.sys.vendor: Dell Inc.
apport information