I'm running Ubuntu 18.04.2 LTS.
I had brightness issues in my Ubuntu so checked out a few forums. From this forum, I followed the instructions and did:
Opened the file /etc/default/grub using gedit or any other text editor. Found below line:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
Changed above line to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
Also created the file /usr/share/X11/xorg.conf.d/80-backlight.conf with contents:
Section "Device"
Identifier "Intel Graphics"
Driver "intel"
Option "AccelMethod" "sna"
Option "Backlight" "acpi_video0"
BusID "PCI:0:2:0"
EndSection
Now Ubuntu won't start. It shows a black screen with the following boot messages.
[ 2.601256] VFS: Cannot open root device "mapper/ubuntu--vg-root" on unknown-block(0,0)
[ 2.601308] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.15.0-48-generic #51~Ubuntu
[ 2.601336] Hardware name: Acer Aspire 47362 / Aspire 47362 BIOS V1.08 08/14/2009
[ 2.601375] Call trace:
[ 2.601412] dump_stack+0x58/0x81
[ 2.601446] panic+0x94/0x1e6
[ 2.601479] mount_block_root+0x199/0x234
[ 2.601514] ? calibrate_delay+190/0x4e0
[ 2.601546] ? create_dev.constrprop.7+0x3a/0x53
[ 2.601581] mount_root+0x33/0x35
[ 2.601612] prepare_namespace+0x11b/0x167
[ 2.601645] kernel_init_freeable+0x1b3/0x1c5
[ 2.601679] ? rest_init+0xa0/0xa0
[ 2.601711] kernel_init+0xd/0x100
[ 2.601744] ret_from_fork+0x2e/0x38
[ 2.601795] Kernel Offset: 0x3d000000 from 8x1a000000 from 8xc1000000 (relocation range: 8xc100000-0xf17dfdfff)
[ 2.601836] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on
unknown-block(0,0)
