permission denied with "touch" even as root user

i just installed manjaro, and as with any other linux os that i have installed recently, there is not monitor brightness adjustment , and my screen is to me too bright, even after i have dial down to the bottom most brightness setting of my monitor.

after reading this forum,
https://www.linuxquestions.org/questions/showthread.php?p=6106138#post6106138
i intended to try out


Try the following:

Code:

sudo su - cd /sys/class/backlight

Now it depends a little on your hardware, but there should be exactly one subfolder (for one monitor), and inside that subfolder should be a file called ‘brightness’
So, cd to that subfolder (on my system it’s intel_backlight):

Code:

cd intel_backlight cat brightness echo 100 > brightness echo 500 > brightness

etc.
I think the values are hardware-specific but on my machine 100% brightness is 800.
Don't use too small values, öest the screen goes dark!


but, to my dismay, even in root user mode, i can't even create a file in /sys/class/backlight/

[backlight]# touch brightness
touch: cannot touch 'brightness': Permission denied
[backlight]# 

my system spec:

inxi -Fxzr
System:    Kernel: 5.4.23-1-MANJARO x86_64 bits: 64 compiler: gcc v: 9.2.1 Desktop: KDE Plasma 5.17.5 
           Distro: Manjaro Linux 
Machine:   Type: Desktop System: Dell product: OptiPlex 755 v: N/A serial: <filter> 
           Mobo: Dell model: 0GM819 serial: <filter> BIOS: Dell v: A19 date: 05/31/2011 
CPU:       Topology: Dual Core model: Intel Core2 Duo E8400 bits: 64 type: MCP arch: Penryn rev: A L2 cache: 6144 KiB 
           flags: lm nx pae sse sse2 sse3 sse4_1 ssse3 vmx bogomips: 11975 
           Speed: 1995 MHz min/max: 2000/3000 MHz Core speeds (MHz): 1: 1995 2: 1995 
Graphics:  Device-1: Intel 82Q35 Express Integrated Graphics vendor: Dell OptiPlex 755 driver: i915 v: kernel 
           bus ID: 00:02.0 
           Display: x11 server: X.Org 1.20.7 driver: intel unloaded: modesetting resolution: 1280x1024~60Hz 
           OpenGL: renderer: Mesa DRI Intel Q35 v: 1.4 Mesa 19.3.4 direct render: Yes 
Audio:     Device-1: Intel 82801I HD Audio vendor: Dell Optiplex 755 driver: snd_hda_intel v: kernel bus ID: 00:1b.0 
           Sound Server: ALSA v: k5.4.23-1-MANJARO 
Network:   Device-1: Intel 82566DM-2 Gigabit Network vendor: Dell OptiPlex 755 driver: e1000e v: 3.2.6-k port: ecc0 
           bus ID: 00:19.0 
           IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: <filter> 
           Device-2: Intel 82557/8/9/0/1 Ethernet Pro 100 driver: e100 v: 3.5.24-k2-NAPI port: dcc0 bus ID: 03:00.0 
           IF: enp3s0 state: down mac: <filter> 
Drives:    Local Storage: total: 465.66 GiB used: 16.70 GiB (3.6%) 
           ID-1: /dev/sda vendor: Seagate model: ST3250310AS size: 232.83 GiB 
           ID-2: /dev/sdb vendor: Seagate model: ST3250318AS size: 232.83 GiB 
Partition: ID-1: / size: 27.59 GiB used: 7.26 GiB (26.3%) fs: ext4 dev: /dev/sda2 
           ID-2: /boot size: 1.92 GiB used: 57.0 MiB (2.9%) fs: ext2 dev: /dev/sda1 
           ID-3: /home size: 183.16 GiB used: 1.51 GiB (0.8%) fs: ext4 dev: /dev/sda4 
Sensors:   System Temperatures: cpu: 34.0 C mobo: N/A 
           Fan Speeds (RPM): N/A 
Repos:     Active pacman repo servers in: /etc/pacman.d/mirrorlist 
           1: https://manjaro.ynh.ovh/stable/$repo/$arch
           2: https://manjaro.mirror.liquidtelecom.com/stable/$repo/$arch
           3: https://download.nus.edu.sg/mirror/manjaro/stable/$repo/$arch
Info:      Processes: 178 Uptime: 13h 06m Memory: 7.64 GiB used: 2.47 GiB (32.4%) Init: systemd Compilers: gcc: 9.2.1 
           Shell: bash v: 5.0.16 inxi: 3.0.37 

can you pls tell me how do you tell my system is out of date ? i just downloaded it yesterday night..
pls guide me on how you judge that my system is out of date. .so that i can fish myself instead of relying spoon feed. i just landed on manjaro.. a lot of thing i don't know and have to start anew like how i was learning ubuntu 3 months ago..

thx

Running sudo pacman -Syu will tell you if there are new updates available. You can answer 'n' if you do not want to continue with the update.

You can also run pacman-mirrors -f to automatically select new mirrors for updates (just in case your old ones are outdated). After that you can refresh the database with sudo pacman -Syyu.

tq.

# inxi -Fzxr
System:    Kernel: 5.4.23-1-MANJARO x86_64 bits: 64 compiler: gcc v: 9.2.1 Console: tty 2 
           Distro: Manjaro Linux 
Machine:   Type: Desktop System: Dell product: OptiPlex 755 v: N/A serial: <filter> 
           Mobo: Dell model: 0GM819 serial: <filter> BIOS: Dell v: A19 date: 05/31/2011 
CPU:       Topology: Dual Core model: Intel Core2 Duo E8400 bits: 64 type: MCP arch: Penryn rev: A L2 cache: 6144 KiB 
           flags: lm nx pae sse sse2 sse3 sse4_1 ssse3 vmx bogomips: 11975 
           Speed: 1995 MHz min/max: 2000/3000 MHz Core speeds (MHz): 1: 1995 2: 1995 
Graphics:  Device-1: Intel 82Q35 Express Integrated Graphics vendor: Dell OptiPlex 755 driver: i915 v: kernel 
           bus ID: 00:02.0 
           Display: server: X.Org 1.20.7 driver: intel unloaded: modesetting resolution: 1280x1024~60Hz 
           OpenGL: renderer: Mesa DRI Intel Q35 v: 1.4 Mesa 19.3.5 direct render: Yes 
Audio:     Device-1: Intel 82801I HD Audio vendor: Dell Optiplex 755 driver: snd_hda_intel v: kernel bus ID: 00:1b.0 
           Sound Server: ALSA v: k5.4.23-1-MANJARO 
Network:   Device-1: Intel 82566DM-2 Gigabit Network vendor: Dell OptiPlex 755 driver: e1000e v: 3.2.6-k port: ecc0 
           bus ID: 00:19.0 
           IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: <filter> 
           Device-2: Intel 82557/8/9/0/1 Ethernet Pro 100 driver: e100 v: 3.5.24-k2-NAPI port: dcc0 bus ID: 03:00.0 
           IF: enp3s0 state: down mac: <filter> 
Drives:    Local Storage: total: 465.66 GiB used: 18.04 GiB (3.9%) 
           ID-1: /dev/sda vendor: Seagate model: ST3250310AS size: 232.83 GiB 
           ID-2: /dev/sdb vendor: Seagate model: ST3250318AS size: 232.83 GiB 
Partition: ID-1: / size: 27.59 GiB used: 8.59 GiB (31.1%) fs: ext4 dev: /dev/sda2 
           ID-2: /boot size: 1.92 GiB used: 57.2 MiB (2.9%) fs: ext2 dev: /dev/sda1 
           ID-3: /home size: 183.16 GiB used: 1.52 GiB (0.8%) fs: ext4 dev: /dev/sda4 
Sensors:   System Temperatures: cpu: 34.0 C mobo: N/A 
           Fan Speeds (RPM): N/A 
Repos:     Active pacman repo servers in: /etc/pacman.d/mirrorlist 
           1: https://manjaro.moson.org/stable/$repo/$arch
           2: https://mirror.futureweb.be/manjaro/stable/$repo/$arch
           3: https://manjaro.osmir.ch/stable/$repo/$arch
           4: https://manjaro.moson.eu/stable/$repo/$arch
           5: https://mirror.koddos.net/manjaro/stable/$repo/$arch
           6: https://mirror.23media.com/manjaro/stable/$repo/$arch
           7: https://mirror.dkm.cz/manjaro/stable/$repo/$arch
           8: https://mirror.netcologne.de/manjaro/stable/$repo/$arch
           9: http://manjaro.mirrors.uk2.net/stable/$repo/$arch
           10: https://quantum-mirror.hu/mirrors/pub/manjaro/stable/$repo/$arch
           11: https://mirror.netzspielplatz.de/manjaro/packages/stable/$repo/$arch
           12: http://mirror.inode.at/manjaro/stable/$repo/$arch
           13: https://nova.quantum-mirror.hu/mirrors/pub/manjaro/stable/$repo/$arch
           14: https://mirror.alpix.eu/manjaro/stable/$repo/$arch
           15: http://kibo.remi.lu/stable/$repo/$arch
           16: https://manjaro.mcofficer.me/stable/$repo/$arch
           17: https://www.mirrorservice.org/sites/repo.manjaro.org/repos/stable/$repo/$arch
           18: https://mirror.zetup.net/manjaro/stable/$repo/$arch
           19: https://ftp.caliu.cat/pub/distribucions/manjaro/stable/$repo/$arch
           20: https://mirror.yandex.ru/mirrors/manjaro/stable/$repo/$arch
           21: http://mirror.datacenter.by/pub/mirrors/manjaro/stable/$repo/$arch
           22: https://ftp.nluug.nl/pub/os/Linux/distr/manjaro/stable/$repo/$arch
           23: https://manjaro.ynh.ovh/stable/$repo/$arch
           24: https://mirrors.dotsrc.org/manjaro/stable/$repo/$arch
           25: http://repo.manjaro.org.uk/stable/$repo/$arch
           26: http://mirror.easyname.at/manjaro/stable/$repo/$arch
           27: http://mirror.terrahost.no/linux/manjaro/stable/$repo/$arch
           28: https://mirror.tuchola-dc.pl/manjaro/stable/$repo/$arch
           29: https://mirrors.netix.net/manjaro/stable/$repo/$arch
           30: https://www.uex.dk/public/manjaro/stable/$repo/$arch
           31: http://ftp.free.org/mirrors/repo.manjaro.org/repos/stable/$repo/$arch
           32: https://ftp.halifax.rwth-aachen.de/manjaro/stable/$repo/$arch
           33: https://manjaro.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           34: http://ftp.tu-chemnitz.de/pub/linux/manjaro/stable/$repo/$arch
           35: https://mirrors.gigenet.com/manjaro/stable/$repo/$arch
           36: https://manjaro.ipacct.com/manjaro/stable/$repo/$arch
           37: https://mirrors.piconets.webwerks.in/manjaro-mirror/stable/$repo/$arch
           38: https://repo.ialab.dsu.edu/manjaro/stable/$repo/$arch
           39: https://mirror.deace.id/manjaro/stable/$repo/$arch
           40: https://ba.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           41: https://ftp.lysator.liu.se/pub/manjaro/stable/$repo/$arch
           42: http://mirror.truenetwork.ru/manjaro/stable/$repo/$arch
           43: https://mirror.math.princeton.edu/pub/manjaro/stable/$repo/$arch
           44: http://mirrors.colocall.net/manjaro/stable/$repo/$arch
           45: https://osmirror.org/manjaro/stable/$repo/$arch
           46: https://manjaro.mirror.liquidtelecom.com/stable/$repo/$arch
           47: http://mirror.xeonbd.com/manjaro/stable/$repo/$arch
           48: http://ftp.vectranet.pl/manjaro/stable/$repo/$arch
           49: http://ftp.linux.org.tr/manjaro/stable/$repo/$arch
           50: https://ftp.cc.uoc.gr/mirrors/linux/manjaro/stable/$repo/$arch
           51: https://mirror.csclub.uwaterloo.ca/manjaro/stable/$repo/$arch
           52: https://mirror.oldsql.cc/manjaro/stable/$repo/$arch
           53: http://distro.ibiblio.org/manjaro/stable/$repo/$arch
           54: http://manjaro.telecoms.bg/stable/$repo/$arch
           55: http://ftp.dei.uc.pt/pub/linux/manjaro/stable/$repo/$arch
           56: https://ct.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           57: http://manjaro.dcc.uchile.cl/stable/$repo/$arch
           58: https://mirrors.ucr.ac.cr/manjaro/stable/$repo/$arch
           59: http://manjaro.mirrors.theom.nz/stable/$repo/$arch
           60: https://mirrors.ocf.berkeley.edu/manjaro/stable/$repo/$arch
           61: http://free.nchc.org.tw/manjaro/stable/$repo/$arch
           62: https://mirror.ufro.cl/manjaro/stable/$repo/$arch
           63: https://manjaro.c3sl.ufpr.br/stable/$repo/$arch
           64: https://download.nus.edu.sg/mirror/manjaro/stable/$repo/$arch
           65: http://manjaro.mirror.serversaustralia.com.au/stable/$repo/$arch
           66: http://kartolo.sby.datautama.net.id/manjaro/stable/$repo/$arch
           67: https://mirror.d-tl.com/manjaro/stable/$repo/$arch
           68: http://mirror.is.co.za/mirrors/manjaro.org/stable/$repo/$arch
           69: https://mirrors.tuna.tsinghua.edu.cn/manjaro/stable/$repo/$arch
           70: https://mirrors.ustc.edu.cn/manjaro/stable/$repo/$arch
           71: https://mirrors.sjtug.sjtu.edu.cn/manjaro/stable/$repo/$arch
           72: https://mirror.kku.ac.th/manjaro/stable/$repo/$arch
           73: http://linorg.usp.br/manjaro/stable/$repo/$arch
           74: https://mirror.clarkson.edu/manjaro/stable/$repo/$arch
           75: http://ftp.cuhk.edu.hk/pub/Linux/manjaro/stable/$repo/$arch
           76: http://ftp.tsukuba.wide.ad.jp/Linux/manjaro/stable/$repo/$arch
           77: http://mirror.rise.ph/manjaro/stable/$repo/$arch
           78: http://ftp.riken.jp/Linux/manjaro/stable/$repo/$arch
Info:      Processes: 178 Uptime: 13h 39m Memory: 7.64 GiB used: 2.44 GiB (31.9%) Init: systemd Compilers: gcc: 9.3.0 
           Shell: bash v: 5.0.16 inxi: 3.0.37 

i tried to locate which "version number of software i have listed" but not sure which are those you refer to.

can pls tell me. tq.

 sudo pacman -Syyu
[sudo] password for manjaro-andrew: 
:: Synchronizing package databases...
 core                                           171,5 KiB  3,89 MiB/s 00:00 [##########################################] 100%
 extra                                         1999,0 KiB  13,3 MiB/s 00:00 [##########################################] 100%
 community                                        5,9 MiB  14,6 MiB/s 00:00 [##########################################] 100%
 multilib                                       192,4 KiB  6,96 MiB/s 00:00 [##########################################] 100%
:: Starting full system upgrade...
 there is nothing to do
inxi -Fxzr
System:    Host: andrew-pc Kernel: 5.4.23-1-MANJARO x86_64 bits: 64 compiler: gcc v: 9.2.1 Console: tty 2 
           Distro: Manjaro Linux 
Machine:   Type: Desktop System: Dell product: OptiPlex 755 v: N/A serial: <filter> 
           Mobo: Dell model: 0GM819 serial: <filter> BIOS: Dell v: A19 date: 05/31/2011 
CPU:       Topology: Dual Core model: Intel Core2 Duo E8400 bits: 64 type: MCP arch: Penryn rev: A L2 cache: 6144 KiB 
           flags: lm nx pae sse sse2 sse3 sse4_1 ssse3 vmx bogomips: 11975 
           Speed: 1995 MHz min/max: 2000/3000 MHz Core speeds (MHz): 1: 1995 2: 1995 
Graphics:  Device-1: Intel 82Q35 Express Integrated Graphics vendor: Dell OptiPlex 755 driver: i915 v: kernel 
           bus ID: 00:02.0 
           Display: server: X.Org 1.20.7 driver: intel unloaded: modesetting resolution: 1280x1024~60Hz 
           OpenGL: renderer: Mesa DRI Intel Q35 v: 1.4 Mesa 19.3.5 direct render: Yes 
Audio:     Device-1: Intel 82801I HD Audio vendor: Dell Optiplex 755 driver: snd_hda_intel v: kernel bus ID: 00:1b.0 
           Sound Server: ALSA v: k5.4.23-1-MANJARO 
Network:   Device-1: Intel 82566DM-2 Gigabit Network vendor: Dell OptiPlex 755 driver: e1000e v: 3.2.6-k port: ecc0 
           bus ID: 00:19.0 
           IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: <filter> 
           Device-2: Intel 82557/8/9/0/1 Ethernet Pro 100 driver: e100 v: 3.5.24-k2-NAPI port: dcc0 bus ID: 03:00.0 
           IF: enp3s0 state: down mac: <filter> 
Drives:    Local Storage: total: 465.66 GiB used: 18.04 GiB (3.9%) 
           ID-1: /dev/sda vendor: Seagate model: ST3250310AS size: 232.83 GiB 
           ID-2: /dev/sdb vendor: Seagate model: ST3250318AS size: 232.83 GiB 
Partition: ID-1: / size: 27.59 GiB used: 8.59 GiB (31.1%) fs: ext4 dev: /dev/sda2 
           ID-2: /boot size: 1.92 GiB used: 57.2 MiB (2.9%) fs: ext2 dev: /dev/sda1 
           ID-3: /home size: 183.16 GiB used: 1.52 GiB (0.8%) fs: ext4 dev: /dev/sda4 
Sensors:   System Temperatures: cpu: 34.0 C mobo: N/A 
           Fan Speeds (RPM): N/A 
Repos:     Active pacman repo servers in: /etc/pacman.d/mirrorlist 
           1: https://manjaro.moson.org/stable/$repo/$arch
           2: https://mirror.futureweb.be/manjaro/stable/$repo/$arch
           3: https://manjaro.osmir.ch/stable/$repo/$arch
           4: https://manjaro.moson.eu/stable/$repo/$arch
           5: https://mirror.koddos.net/manjaro/stable/$repo/$arch
           6: https://mirror.23media.com/manjaro/stable/$repo/$arch
           7: https://mirror.dkm.cz/manjaro/stable/$repo/$arch
           8: https://mirror.netcologne.de/manjaro/stable/$repo/$arch
           9: http://manjaro.mirrors.uk2.net/stable/$repo/$arch
           10: https://quantum-mirror.hu/mirrors/pub/manjaro/stable/$repo/$arch
           11: https://mirror.netzspielplatz.de/manjaro/packages/stable/$repo/$arch
           12: http://mirror.inode.at/manjaro/stable/$repo/$arch
           13: https://nova.quantum-mirror.hu/mirrors/pub/manjaro/stable/$repo/$arch
           14: https://mirror.alpix.eu/manjaro/stable/$repo/$arch
           15: http://kibo.remi.lu/stable/$repo/$arch
           16: https://manjaro.mcofficer.me/stable/$repo/$arch
           17: https://www.mirrorservice.org/sites/repo.manjaro.org/repos/stable/$repo/$arch
           18: https://mirror.zetup.net/manjaro/stable/$repo/$arch
           19: https://ftp.caliu.cat/pub/distribucions/manjaro/stable/$repo/$arch
           20: https://mirror.yandex.ru/mirrors/manjaro/stable/$repo/$arch
           21: http://mirror.datacenter.by/pub/mirrors/manjaro/stable/$repo/$arch
           22: https://ftp.nluug.nl/pub/os/Linux/distr/manjaro/stable/$repo/$arch
           23: https://manjaro.ynh.ovh/stable/$repo/$arch
           24: https://mirrors.dotsrc.org/manjaro/stable/$repo/$arch
           25: http://repo.manjaro.org.uk/stable/$repo/$arch
           26: http://mirror.easyname.at/manjaro/stable/$repo/$arch
           27: http://mirror.terrahost.no/linux/manjaro/stable/$repo/$arch
           28: https://mirror.tuchola-dc.pl/manjaro/stable/$repo/$arch
           29: https://mirrors.netix.net/manjaro/stable/$repo/$arch
           30: https://www.uex.dk/public/manjaro/stable/$repo/$arch
           31: http://ftp.free.org/mirrors/repo.manjaro.org/repos/stable/$repo/$arch
           32: https://ftp.halifax.rwth-aachen.de/manjaro/stable/$repo/$arch
           33: https://manjaro.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           34: http://ftp.tu-chemnitz.de/pub/linux/manjaro/stable/$repo/$arch
           35: https://mirrors.gigenet.com/manjaro/stable/$repo/$arch
           36: https://manjaro.ipacct.com/manjaro/stable/$repo/$arch
           37: https://mirrors.piconets.webwerks.in/manjaro-mirror/stable/$repo/$arch
           38: https://repo.ialab.dsu.edu/manjaro/stable/$repo/$arch
           39: https://mirror.deace.id/manjaro/stable/$repo/$arch
           40: https://ba.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           41: https://ftp.lysator.liu.se/pub/manjaro/stable/$repo/$arch
           42: http://mirror.truenetwork.ru/manjaro/stable/$repo/$arch
           43: https://mirror.math.princeton.edu/pub/manjaro/stable/$repo/$arch
           44: http://mirrors.colocall.net/manjaro/stable/$repo/$arch
           45: https://osmirror.org/manjaro/stable/$repo/$arch
           46: https://manjaro.mirror.liquidtelecom.com/stable/$repo/$arch
           47: http://mirror.xeonbd.com/manjaro/stable/$repo/$arch
           48: http://ftp.vectranet.pl/manjaro/stable/$repo/$arch
           49: http://ftp.linux.org.tr/manjaro/stable/$repo/$arch
           50: https://ftp.cc.uoc.gr/mirrors/linux/manjaro/stable/$repo/$arch
           51: https://mirror.csclub.uwaterloo.ca/manjaro/stable/$repo/$arch
           52: https://mirror.oldsql.cc/manjaro/stable/$repo/$arch
           53: http://distro.ibiblio.org/manjaro/stable/$repo/$arch
           54: http://manjaro.telecoms.bg/stable/$repo/$arch
           55: http://ftp.dei.uc.pt/pub/linux/manjaro/stable/$repo/$arch
           56: https://ct.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           57: http://manjaro.dcc.uchile.cl/stable/$repo/$arch
           58: https://mirrors.ucr.ac.cr/manjaro/stable/$repo/$arch
           59: http://manjaro.mirrors.theom.nz/stable/$repo/$arch
           60: https://mirrors.ocf.berkeley.edu/manjaro/stable/$repo/$arch
           61: http://free.nchc.org.tw/manjaro/stable/$repo/$arch
           62: https://mirror.ufro.cl/manjaro/stable/$repo/$arch
           63: https://manjaro.c3sl.ufpr.br/stable/$repo/$arch
           64: https://download.nus.edu.sg/mirror/manjaro/stable/$repo/$arch
           65: http://manjaro.mirror.serversaustralia.com.au/stable/$repo/$arch
           66: http://kartolo.sby.datautama.net.id/manjaro/stable/$repo/$arch
           67: https://mirror.d-tl.com/manjaro/stable/$repo/$arch
           68: http://mirror.is.co.za/mirrors/manjaro.org/stable/$repo/$arch
           69: https://mirrors.tuna.tsinghua.edu.cn/manjaro/stable/$repo/$arch
           70: https://mirrors.ustc.edu.cn/manjaro/stable/$repo/$arch
           71: https://mirrors.sjtug.sjtu.edu.cn/manjaro/stable/$repo/$arch
           72: https://mirror.kku.ac.th/manjaro/stable/$repo/$arch
           73: http://linorg.usp.br/manjaro/stable/$repo/$arch
           74: https://mirror.clarkson.edu/manjaro/stable/$repo/$arch
           75: http://ftp.cuhk.edu.hk/pub/Linux/manjaro/stable/$repo/$arch
           76: http://ftp.tsukuba.wide.ad.jp/Linux/manjaro/stable/$repo/$arch
           77: http://mirror.rise.ph/manjaro/stable/$repo/$arch
           78: http://ftp.riken.jp/Linux/manjaro/stable/$repo/$arch
Info:      Processes: 176 Uptime: 13h 48m Memory: 7.64 GiB used: 2.62 GiB (34.3%) Init: systemd Compilers: gcc: 9.3.0 
           Shell: bash v: 5.0.16 inxi: 3.0.37 

Open a terminal:

su #Enter password
cd /sys/class/backlight
#

Then:

ls -lah
Permissions Size User Date Modified    Name
lrwxrwxrwx     0 root 2020-03-31 10:56 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight
cd intel_backlight
ls -lah
Permissions Size User Date Modified    Name
.r--r--r--  4.1k root 2020-03-31 10:59 actual_brightness
.rw-r--r--  4.1k root 2020-03-31 10:59 bl_power
.rw-rw-r--  4.1k root 2020-03-30 23:34 brightness
lrwxrwxrwx     0 root 2020-03-31 10:59 device -> ../../card0-eDP-1
.r--r--r--  4.1k root 2020-03-31 10:59 max_brightness
drwxr-xr-x     - root 2020-03-31 10:59 power
.r--r--r--  4.1k root 2020-03-31 10:59 scale
lrwxrwxrwx     0 root 2020-03-31 10:59 subsystem -> ../../../../../../../class/backlight
.r--r--r--  4.1k root 2020-03-31 10:59 type
.rw-r--r--  4.1k root 2020-03-31 10:59 uevent

It is a symbolic link to a directory

Can you post the output of the ls command above?

That's easy to tell:

inxi -Fxzr
System:    Host: andrew-pc Kernel: 5.4.23-1-MANJARO

Roughly one month behind.

there u go. there is nothing in the backlight folder

$ sudo cd /sys/class/backlight
sudo: cd: command not found
[manjaro-andrew@andrew-pc /]$ cd /sys/class/
[manjaro-andrew@andrew-pc class]$ ls
ata_device  dax            drm_dp_aux_dev  input  nvme            ppdev       rtc           spi_slave  watchdog
ata_link    devcoredump    extcon          iommu  nvme-subsystem  pps         scsi_device   thermal
ata_port    devfreq        gpio            leds   pci_bus         ptp         scsi_disk     tty
backlight   devfreq-event  graphics        mem    pci_epc         pwm         scsi_generic  usbmisc
bdi         dma            hidraw          misc   phy             regulator   scsi_host     vc
block       dmi            hwmon           nd     powercap        remoteproc  sound         vtconsole
bsg         drm            i2c-adapter     net    power_supply    rfkill      spi_master    wakeup
[manjaro-andrew@andrew-pc class]$ cd backlight
[manjaro-andrew@andrew-pc backlight]$ ls -a
.  ..

hii, thank you for answering me.

[Yorper] told me to update my manjaro, using command :

 sudo pacman -Syu 

and

sudo pacman -Syyu to update cache database,
but after i have done all the required steps, my kernel is still 5.4.23-1-MANJARO
.. why is that ?

thx

cat backlight

From the first folder. What does it contain?

sorry, i don't really understand what you want. so i did what i think you may wanted me to do:

$ cat /sys/class/backlight
cat: /sys/class/backlight: Is a directory
[manjaro-andrew@andrew-pc /]$ cat /sys/class/backlight/*
cat: '/sys/class/backlight/*': No such file or directory
[manjaro-andrew@andrew-pc /]$ cat /backlight
cat: /backlight: No such file or directory
[manjaro-andrew@andrew-pc /]$ cat /backlight/
cat: /backlight/: No such file or directory
[manjaro-andrew@andrew-pc /]$ cat /sys/class/backlight/
cat: /sys/class/backlight/: Is a directory
[manjaro-andrew@andrew-pc /]$ cd /sys/class
[manjaro-andrew@andrew-pc class]$ ls
ata_device  block        devfreq-event   extcon    i2c-adapter  misc            pci_bus       ppdev      remoteproc   scsi_generic  thermal    wakeup
ata_link    bsg          dma             gpio      input        nd              pci_epc       pps        rfkill       scsi_host     tty        watchdog
ata_port    dax          dmi             graphics  iommu        net             phy           ptp        rtc          sound         usbmisc
backlight   devcoredump  drm             hidraw    leds         nvme            powercap      pwm        scsi_device  spi_master    vc
bdi         devfreq      drm_dp_aux_dev  hwmon     mem          nvme-subsystem  power_supply  regulator  scsi_disk    spi_slave     vtconsole
[manjaro-andrew@andrew-pc class]$ cd backlight
[manjaro-andrew@andrew-pc backlight]$ ls
[manjaro-andrew@andrew-pc backlight]$ cd ..
[manjaro-andrew@andrew-pc class]$ cat backlight
cat: backlight: Is a directory

The command is ls -lah - it shows full info - with ls you cannot tell the difference between file and directory, when posted here.

Try this:

su
cd /sys/class/backlight
echo 800 > brightness
reboot

execute

sudo pacman-mirrors -f

in terminal, then

sudo pacman -Syyu

But first finish your work with xircon, don't deal with two different issues at once.

His system may or may not be up-to-date. It is irrelevant to the problem he is encountering. @weissbrot et al.

done.

 sudo pacman-mirrors -f
[sudo] password for manjaro-andrew: 
::INFO Downloading mirrors from repo.manjaro.org
::INFO Using default mirror file
::INFO Querying mirrors - This may take some time
  1.088 United_States  : http://distro.ibiblio.org/manjaro/
  1.387 Costa_Rica     : https://mirrors.ucr.ac.cr/manjaro/
  0.259 United_Kingdom : https://www.mirrorservice.org/sites/repo.manjaro.org/repos/
  0.803 United_States  : https://mirror.math.princeton.edu/pub/manjaro/
  0.540 Portugal       : http://ftp.dei.uc.pt/pub/linux/manjaro/
  1.349 Bulgaria       : http://manjaro.telecoms.bg/
  0.423 Bulgaria       : https://manjaro.ipacct.com/manjaro/
  2.729 Singapore      : https://download.nus.edu.sg/mirror/manjaro/
  3.338 Thailand       : https://mirror.kku.ac.th/manjaro/
::INFO Writing mirror list
::Germany         : https://mirror.23media.com/manjaro/stable
::Belgium         : https://mirror.futureweb.be/manjaro/stable
::Switzerland     : https://manjaro.osmir.ch/stable
::Germany         : https://manjaro.moson.org/stable
::Netherlands     : https://mirror.koddos.net/manjaro/stable
::Germany         : https://mirror.netzspielplatz.de/manjaro/packages/stable
::Czech           : https://mirror.dkm.cz/manjaro/stable
::Germany         : https://mirror.netcologne.de/manjaro/stable
::France          : http://kibo.remi.lu/stable
::Hungary         : https://nova.quantum-mirror.hu/mirrors/pub/manjaro/stable
::France          : https://manjaro.mcofficer.me/stable
::Germany         : https://mirror.alpix.eu/manjaro/stable
::Germany         : https://manjaro.moson.eu/stable
::France          : https://manjaro.ynh.ovh/stable
::United_Kingdom  : https://www.mirrorservice.org/sites/repo.manjaro.org/repos/stable
::Hungary         : https://quantum-mirror.hu/mirrors/pub/manjaro/stable
::Austria         : http://mirror.inode.at/manjaro/stable
::Russia          : https://mirror.yandex.ru/mirrors/manjaro/stable
::Netherlands     : http://ftp.snt.utwente.nl/pub/linux/manjaro/stable
::Denmark         : https://mirrors.dotsrc.org/manjaro/stable
::Spain           : https://ftp.caliu.cat/pub/distribucions/manjaro/stable
::Norway          : http://mirror.terrahost.no/linux/manjaro/stable
::Denmark         : https://www.uex.dk/public/manjaro/stable
::Netherlands     : https://ftp.nluug.nl/pub/os/Linux/distr/manjaro/stable
::Sweden          : https://mirror.zetup.net/manjaro/stable
::Austria         : http://mirror.easyname.at/manjaro/stable
::Bulgaria        : https://manjaro.ipacct.com/manjaro/stable
::Belarus         : http://mirror.datacenter.by/pub/mirrors/manjaro/stable
::France          : http://ftp.free.org/mirrors/repo.manjaro.org/repos/stable
::Germany         : http://ftp.tu-chemnitz.de/pub/linux/manjaro/stable
::Italy           : https://manjaro.mirror.garr.it/mirrors/manjaro/stable
::Italy           : https://ct.mirror.garr.it/mirrors/manjaro/stable
::Portugal        : http://ftp.dei.uc.pt/pub/linux/manjaro/stable
::Germany         : https://ftp.halifax.rwth-aachen.de/manjaro/stable
::Italy           : https://ba.mirror.garr.it/mirrors/manjaro/stable
::United_States   : https://mirrors.gigenet.com/manjaro/stable
::United_States   : https://repo.ialab.dsu.edu/manjaro/stable
::Russia          : http://mirror.truenetwork.ru/manjaro/stable
::United_States   : https://mirror.math.princeton.edu/pub/manjaro/stable
::Indonesia       : https://mirror.deace.id/manjaro/stable
::Bangladesh      : http://mirror.xeonbd.com/manjaro/stable
::Canada          : https://osmirror.org/manjaro/stable
::Canada          : https://mirror.csclub.uwaterloo.ca/manjaro/stable
::Turkey          : http://ftp.linux.org.tr/manjaro/stable
::United_States   : https://mirror.clarkson.edu/manjaro/stable
::Ukraine         : http://mirrors.colocall.net/manjaro/stable
::India           : https://mirrors.piconets.webwerks.in/manjaro-mirror/stable
::United_States   : http://distro.ibiblio.org/manjaro/stable
::South_Africa    : http://mirror.is.co.za/mirrors/manjaro.org/stable
::Greece          : https://ftp.cc.uoc.gr/mirrors/linux/manjaro/stable
::Poland          : http://ftp.vectranet.pl/manjaro/stable
::Sweden          : https://ftp.lysator.liu.se/pub/manjaro/stable
::France          : https://mirror.oldsql.cc/manjaro/stable
::Bulgaria        : https://mirrors.netix.net/manjaro/stable
::Bulgaria        : http://manjaro.telecoms.bg/stable
::Costa_Rica      : https://mirrors.ucr.ac.cr/manjaro/stable
::Brazil          : https://manjaro.c3sl.ufpr.br/stable
::Chile           : http://manjaro.dcc.uchile.cl/stable
::Kenya           : https://manjaro.mirror.liquidtelecom.com/stable
::New_Zealand     : http://manjaro.mirrors.theom.nz/stable
::United_States   : https://mirrors.ocf.berkeley.edu/manjaro/stable
::Chile           : https://mirror.ufro.cl/manjaro/stable
::Taiwan          : http://free.nchc.org.tw/manjaro/stable
::Australia       : http://manjaro.mirror.serversaustralia.com.au/stable
::Indonesia       : http://kartolo.sby.datautama.net.id/manjaro/stable
::South_Korea     : https://mirror.d-tl.com/manjaro/stable
::Singapore       : https://download.nus.edu.sg/mirror/manjaro/stable
::China           : https://mirrors.sjtug.sjtu.edu.cn/manjaro/stable
::Hong_Kong       : http://ftp.cuhk.edu.hk/pub/Linux/manjaro/stable
::Thailand        : https://mirror.kku.ac.th/manjaro/stable
::Poland          : https://mirror.tuchola-dc.pl/manjaro/stable
::Japan           : http://ftp.riken.jp/Linux/manjaro/stable
::Philippines     : http://mirror.rise.ph/manjaro/stable
::United_Kingdom  : http://manjaro.mirrors.uk2.net/stable
::Japan           : http://ftp.tsukuba.wide.ad.jp/Linux/manjaro/stable
::China           : https://mirrors.tuna.tsinghua.edu.cn/manjaro/stable
::United_Kingdom  : http://repo.manjaro.org.uk/stable
::Brazil          : http://linorg.usp.br/manjaro/stable
::INFO Mirror list generated and saved to: /etc/pacman.d/mirrorlist

That's why i added

done also

sudo pacman -Syyu
[sudo] password for manjaro-andrew: 
:: Synchronizing package databases...
 core                                                                                                                      171,5 KiB  3,10 MiB/s 00:00 [#####
 extra                                                                                                                    1999,0 KiB  13,6 MiB/s 00:00 [#####
 community                                                                                                                   5,9 MiB  14,9 MiB/s 00:00 [#####
 multilib                                                                                                                  192,4 KiB  6,96 MiB/s 00:00 [#####
:: Starting full system upgrade...
 there is nothing to do

after update, still the same kernel version.. kernel version didn't change

$ inxi -Fxzr
System:    Host: andrew-pc Kernel: 5.4.23-1-MANJARO x86_64 bits: 64 compiler: gcc v: 9.2.1 Desktop: KDE Plasma 5.18.3 
           Distro: Manjaro Linux 
Machine:   Type: Desktop System: Dell product: OptiPlex 755 v: N/A serial: <filter> 
           Mobo: Dell model: 0GM819 serial: <filter> BIOS: Dell v: A19 date: 05/31/2011 
CPU:       Topology: Dual Core model: Intel Core2 Duo E8400 bits: 64 type: MCP arch: Penryn rev: A L2 cache: 6144 KiB 
           flags: lm nx pae sse sse2 sse3 sse4_1 ssse3 vmx bogomips: 11975 
           Speed: 1995 MHz min/max: 2000/3000 MHz Core speeds (MHz): 1: 1995 2: 1995 
Graphics:  Device-1: Intel 82Q35 Express Integrated Graphics vendor: Dell OptiPlex 755 driver: i915 v: kernel bus ID: 00:02.0 
           Display: x11 server: X.Org 1.20.7 driver: intel unloaded: modesetting resolution: 1280x1024~60Hz 
           OpenGL: renderer: Mesa DRI Intel Q35 v: 1.4 Mesa 19.3.5 direct render: Yes 
Audio:     Device-1: Intel 82801I HD Audio vendor: Dell Optiplex 755 driver: snd_hda_intel v: kernel bus ID: 00:1b.0 
           Sound Server: ALSA v: k5.4.23-1-MANJARO 
Network:   Device-1: Intel 82566DM-2 Gigabit Network vendor: Dell OptiPlex 755 driver: e1000e v: 3.2.6-k port: ecc0 
           bus ID: 00:19.0 
           IF: enp0s25 state: up speed: 1000 Mbps duplex: full mac: <filter> 
           Device-2: Intel 82557/8/9/0/1 Ethernet Pro 100 driver: e100 v: 3.5.24-k2-NAPI port: dcc0 bus ID: 03:00.0 
           IF: enp3s0 state: down mac: <filter> 
Drives:    Local Storage: total: 465.66 GiB used: 23.45 GiB (5.0%) 
           ID-1: /dev/sda vendor: Seagate model: ST3250310AS size: 232.83 GiB 
           ID-2: /dev/sdb vendor: Seagate model: ST3250318AS size: 232.83 GiB 
Partition: ID-1: / size: 27.59 GiB used: 8.59 GiB (31.1%) fs: ext4 dev: /dev/sda2 
           ID-2: /boot size: 1.92 GiB used: 57.2 MiB (2.9%) fs: ext2 dev: /dev/sda1 
           ID-3: /home size: 183.16 GiB used: 1.52 GiB (0.8%) fs: ext4 dev: /dev/sda4 
Sensors:   System Temperatures: cpu: 34.0 C mobo: N/A 
           Fan Speeds (RPM): N/A 
Repos:     Active pacman repo servers in: /etc/pacman.d/mirrorlist 
           1: https://mirror.23media.com/manjaro/stable/$repo/$arch
           2: https://mirror.futureweb.be/manjaro/stable/$repo/$arch
           3: https://manjaro.osmir.ch/stable/$repo/$arch
           4: https://manjaro.moson.org/stable/$repo/$arch
           5: https://mirror.koddos.net/manjaro/stable/$repo/$arch
           6: https://mirror.netzspielplatz.de/manjaro/packages/stable/$repo/$arch
           7: https://mirror.dkm.cz/manjaro/stable/$repo/$arch
           8: https://mirror.netcologne.de/manjaro/stable/$repo/$arch
           9: http://kibo.remi.lu/stable/$repo/$arch
           10: https://nova.quantum-mirror.hu/mirrors/pub/manjaro/stable/$repo/$arch
           11: https://manjaro.mcofficer.me/stable/$repo/$arch
           12: https://mirror.alpix.eu/manjaro/stable/$repo/$arch
           13: https://manjaro.moson.eu/stable/$repo/$arch
           14: https://manjaro.ynh.ovh/stable/$repo/$arch
           15: https://www.mirrorservice.org/sites/repo.manjaro.org/repos/stable/$repo/$arch
           16: https://quantum-mirror.hu/mirrors/pub/manjaro/stable/$repo/$arch
           17: http://mirror.inode.at/manjaro/stable/$repo/$arch
           18: https://mirror.yandex.ru/mirrors/manjaro/stable/$repo/$arch
           19: http://ftp.snt.utwente.nl/pub/linux/manjaro/stable/$repo/$arch
           20: https://mirrors.dotsrc.org/manjaro/stable/$repo/$arch
           21: https://ftp.caliu.cat/pub/distribucions/manjaro/stable/$repo/$arch
           22: http://mirror.terrahost.no/linux/manjaro/stable/$repo/$arch
           23: https://www.uex.dk/public/manjaro/stable/$repo/$arch
           24: https://ftp.nluug.nl/pub/os/Linux/distr/manjaro/stable/$repo/$arch
           25: https://mirror.zetup.net/manjaro/stable/$repo/$arch
           26: http://mirror.easyname.at/manjaro/stable/$repo/$arch
           27: https://manjaro.ipacct.com/manjaro/stable/$repo/$arch
           28: http://mirror.datacenter.by/pub/mirrors/manjaro/stable/$repo/$arch
           29: http://ftp.free.org/mirrors/repo.manjaro.org/repos/stable/$repo/$arch
           30: http://ftp.tu-chemnitz.de/pub/linux/manjaro/stable/$repo/$arch
           31: https://manjaro.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           32: https://ct.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           33: http://ftp.dei.uc.pt/pub/linux/manjaro/stable/$repo/$arch
           34: https://ftp.halifax.rwth-aachen.de/manjaro/stable/$repo/$arch
           35: https://ba.mirror.garr.it/mirrors/manjaro/stable/$repo/$arch
           36: https://mirrors.gigenet.com/manjaro/stable/$repo/$arch
           37: https://repo.ialab.dsu.edu/manjaro/stable/$repo/$arch
           38: http://mirror.truenetwork.ru/manjaro/stable/$repo/$arch
           39: https://mirror.math.princeton.edu/pub/manjaro/stable/$repo/$arch
           40: https://mirror.deace.id/manjaro/stable/$repo/$arch
           41: http://mirror.xeonbd.com/manjaro/stable/$repo/$arch
           42: https://osmirror.org/manjaro/stable/$repo/$arch
           43: https://mirror.csclub.uwaterloo.ca/manjaro/stable/$repo/$arch
           44: http://ftp.linux.org.tr/manjaro/stable/$repo/$arch
           45: https://mirror.clarkson.edu/manjaro/stable/$repo/$arch
           46: http://mirrors.colocall.net/manjaro/stable/$repo/$arch
           47: https://mirrors.piconets.webwerks.in/manjaro-mirror/stable/$repo/$arch
           48: http://distro.ibiblio.org/manjaro/stable/$repo/$arch
           49: http://mirror.is.co.za/mirrors/manjaro.org/stable/$repo/$arch
           50: https://ftp.cc.uoc.gr/mirrors/linux/manjaro/stable/$repo/$arch
           51: http://ftp.vectranet.pl/manjaro/stable/$repo/$arch
           52: https://ftp.lysator.liu.se/pub/manjaro/stable/$repo/$arch
           53: https://mirror.oldsql.cc/manjaro/stable/$repo/$arch
           54: https://mirrors.netix.net/manjaro/stable/$repo/$arch
           55: http://manjaro.telecoms.bg/stable/$repo/$arch
           56: https://mirrors.ucr.ac.cr/manjaro/stable/$repo/$arch
           57: https://manjaro.c3sl.ufpr.br/stable/$repo/$arch
           58: http://manjaro.dcc.uchile.cl/stable/$repo/$arch
           59: https://manjaro.mirror.liquidtelecom.com/stable/$repo/$arch
           60: http://manjaro.mirrors.theom.nz/stable/$repo/$arch
           61: https://mirrors.ocf.berkeley.edu/manjaro/stable/$repo/$arch
           62: https://mirror.ufro.cl/manjaro/stable/$repo/$arch
           63: http://free.nchc.org.tw/manjaro/stable/$repo/$arch
           64: http://manjaro.mirror.serversaustralia.com.au/stable/$repo/$arch
           65: http://kartolo.sby.datautama.net.id/manjaro/stable/$repo/$arch
           66: https://mirror.d-tl.com/manjaro/stable/$repo/$arch
           67: https://download.nus.edu.sg/mirror/manjaro/stable/$repo/$arch
           68: https://mirrors.sjtug.sjtu.edu.cn/manjaro/stable/$repo/$arch
           69: http://ftp.cuhk.edu.hk/pub/Linux/manjaro/stable/$repo/$arch
           70: https://mirror.kku.ac.th/manjaro/stable/$repo/$arch
           71: https://mirror.tuchola-dc.pl/manjaro/stable/$repo/$arch
           72: http://ftp.riken.jp/Linux/manjaro/stable/$repo/$arch
           73: http://mirror.rise.ph/manjaro/stable/$repo/$arch
           74: http://manjaro.mirrors.uk2.net/stable/$repo/$arch
           75: http://ftp.tsukuba.wide.ad.jp/Linux/manjaro/stable/$repo/$arch
           76: https://mirrors.tuna.tsinghua.edu.cn/manjaro/stable/$repo/$arch
           77: http://repo.manjaro.org.uk/stable/$repo/$arch
           78: http://linorg.usp.br/manjaro/stable/$repo/$arch
Info:      Processes: 165 Uptime: 16h 33m Memory: 7.64 GiB used: 3.18 GiB (41.6%) Init: systemd Compilers: gcc: 9.3.0 
           Shell: bash v: 5.0.16 inxi: 3.0.37 

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