search

vmatare / thinkfan

The minimalist fan control program
GNU General Public License v3.0
541 stars 62 forks source link

permission denied when trying to set the level (x1 yoga gen 6) #166

Closed salvoc81 closed 2 years ago

salvoc81 commented 2 years ago

When I try to set level I get the following error:

sudo echo level 1 > /proc/acpi/ibm/fan
bash: /proc/acpi/ibm/fan: Permission denied

Any suggestion regarding possible solutions? Thanks a lot.

vmatare commented 2 years ago

Although it's a different error it might be the same issue as in #165. You can check the module options like this:

cat /sys/module/thinkpad_acpi/parameters/fan_control

(edit: fixed typo in path)

koutheir commented 2 years ago

The actual path is /sys/module/thinkpad_acpi/parameters/fan_control.

$ cat /sys/module/thinkpad_acpi/parameters/fan_control
Y
salvoc81 commented 2 years ago

Hello @vmatare and @koutheir
The content of that file is the same for me. 

$ cat /sys/module/thinkpad_acpi/parameters/fan_control
Y

And following are the permissions

$ exa -l /sys/module/thinkpad_acpi/parameters/fan_control
.r--r--r-- 4.1k root 18 11月 10:16 /sys/module/thinkpad_acpi/parameters/fan_control

Do you have the same permission for this file?

koutheir commented 2 years ago

Do you have the same permission for this file?

Yes:

$ ls -lh /sys/module/thinkpad_acpi/parameters/fan_control
-r--r--r-- 1 root root 4.0K Nov 18 09:24 /sys/module/thinkpad_acpi/parameters/fan_control
vmatare commented 2 years ago

oh sorry, it's a very simple error in using sudo. The file redirection takes place before the sudo, i.e. when you do sudo echo bla > something, the file something is opened with your user ID, not as root.

koutheir commented 2 years ago

My bad, I just read your original question. Let me explain what's actually going on.

$ sudo echo level 1 > /proc/acpi/ibm/fan
  ^    ^    ^     ^ ^ ^
  1    2    3     4 5 6

The line above is executed as follows by your shell:

  1. Open /proc/acpi/ibm/fan (because 6) for writing and set it as the standard output (because 5) of sudo (because 1).
  2. Run sudo with arguments 2, 3 and 4.

The command 2, 3 and 4 will run in privileged mode thanks to sudo. That is probably what you expect.

However, the file /proc/acpi/ibm/fan will be open for writing by your shell, not by sudo. Because your shell is unprivileged, that file cannot be open for writing, and your shell receives the Permission denied error due to that, and step (1) above fails.

There are multiple ways to fix this, all of them try to ensure that the command inside sudo is the one that opens the file for writing. You can use the command tee for this purpose, or create another shell that runs the command inside the sudo command, or use su instead. I personally prefer using tee for this.