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I for the life of me still can't wrap my mind around bitmasks. I am sure they are very simple, I just haven't found something that makes how they work click in my brain yet.

What would be the bitmask value that I need to put into /proc/sys/kernel/sysrq to only allow these SysRq commands? ✓ represents enabled command, X represents disabled commands:

✓  r - 4=0x4   - Puts the keyboard into raw mode
✓  k - 4=0x4   - Kills all programs on the current virtual console
✓  s - 16=0x10  - Flushes data from your cache to disk
X  u - 32=0x20  - Remounts all file systems read-only
X  e - 64=0x40  - Sends the terminate signal to all processes
X  i - 64=0x40  - Sends the kill signal to all processes
X  b - 128=0x80 - Reboots your computer
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You just add the values that you want to be active. However, bitmask values are supposed to be unique. So I guess the value of r & k switch should be different. According to this answer, 4 deals with keyboard controls, instead of kill all program. Assuming that all you need is r & s switch, you want the 4+16=20 value

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