bash - echo: write error: invalid argument

Question

I am new to bash and trying to write a script that disables kworker business as in aMaia's answer here.

So far, I have this, which I run from root:

  1 #!/bin/bash                                                                      
  2                                                                                  
  3 cd /sys/firmware/acpi/interrupts                                                 
  4 for i in gpe[[:digit:]]* # Don't mess with gpe_all                               
  5 do                                                                               
  6     num=`awk '{print $1}' $i`                                                    
  7     if (( $num >= 1000 )); then  # potential CPU hogs?                           
  8         # Back it up and then disable it!!                                       
  9         cp $i /root/${i}.backup                                                  
 10         echo "disable" > $i                                                      
 11     fi                                                                           
 12 done  

But running it results in:

./kkiller: line 10: echo: write error: Invalid argument

What is going on here? I thought $i was just the file name, which seems like the correct syntax for echo.

Suggestions for cleaning up/improving the script in general are also appreciated!

Update: With set -vx added to the top of the script, here is a problematic iteration:

+ for i in 'gpe[[:digit:]]*'
awk '{print $1}' $i
++ awk '{print $1}' gpe66
+ num=1024908
+ ((  1024908 >= 1000  ))
+ cp gpe66 /root/gpe66.backup
+ echo disable
./kkiller: line 10: echo: write error: Invalid argument

Answer 1

I had this problem too in Docker on Alpine linux environment. I think the problem is that echo by default put a newline character at the end of the string, and the kernel not accept it, but it is not the case in every system. In Docker I had this error, but the value was written despite the error message.

The solution (in Bash): echo -n disable >/sys/firmware/acpi/interrupts/gpe66. This way no newline is echoed.

Answer 2

Double-check all spelling. echo "disabled" will emit a write error even for root whereas echo "disable" succeeds.