"Attempted to kill init!" https://github.com/torvalds/linux/blob/0b5547c51827e053cc754...

"...and that's why we have to put half a million lines of C in PID 1"

i'm reasonably sure that kill -1 1 used to be a canonical way to `halt`

I used to work with a long-time AIX kernel developer. His method of shutting off his machine was "sync; sync; kill -9 1".

Of course, his method of preparing to move offices (a common occurrence at IBM) was to

1. Take his (RS-6000) workstation home with him the night of the move.

2. Otherwise, just lock his desk.

He didn't have anything in his office but his chair, desk, and workstation.

As a random trivia about sysadmins: the reason he sync-ed twice is not because "twice is better than once, just to make sure".

Sync is not synchronous. When it is back to the shell there is no guarantee that data in memory is fully copied to disk.

However, it sets a flag that is reset when the copying is done. Sync will hang if the flag is set.

So the first sync arms the copy and sets the flag and is back to the shell.

The second sync starts, blocks at the flag. The flag gets reset and it is back to the shell.

So the 2nd sync going back to the shell is a guarantee that the first sync is fine and data is safe