On my Ubuntu VM:

Linux xxxxxxx 3.19.0-25-generic #26~14.04.1-Ubuntu SMP Fri Jul 24
21:16:20 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux

to which I am connected over SSH, I am running this command:

sar 1 10000 | awk '{print $9}'  | grep -v aaaa

(strangely) this command doesn’t produce any output (why?) but next thing is even stranger. If I press Control-C while the command is running it is kind of sending Control-Alt-Delete to my server and the server reboots (why?).

root@xxxxxxx:~# sar 1 10000 | awk '{print $9}'  | grep -v aaaa
Broadcast message from root@xxxxxx 
       (unknown) at 12:01 ...

The system is going down for reboot NOW!
Control-Alt-Delete pressed

thanks for your help.

Best regards Jaor


While described situation sounds quite unrealistic it is actually a fact and is caused by a bug in systat, sadc in particular. sar process spawns sadc process.

TL;DR - Interrupting sar before sadc completes it's job makes sadc triggering a reboot.

Solution to this is to update sysstat to a reasonably new version (the fix is from 2014). From the commit it seems this should be fixed in systat 12.1.7 (not sure about this - still this is a fix from over 5 years ago, understood ubuntu 14 is pretty old). https://github.com/sysstat/sysstat/commit/c3de69658006af0e0e3b7746e8646b8b4cdd2860

more details can be found here


UPDATE: as for no results - this is unrelated thing and is caused by the fact that awk by default is buffering it's input - to get results instantly it needs to be invoked as awk -W interactive

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