This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open There is lots of Linux, Mac OS X and general Unix info elsewhere on this site: Search this site is the best way to find anything.
The /etc/rc[0-2] script scripts use the "prc_sync" command to execute the scripts in the /etc/rc[0-2].d directories. By default, these are run with an argument of "120", which tells prc_sync that the scripts are expected to finish in 2 minutes or less. This time out is managed by prc_sync setting OS level "alarms" ( man S alarm). It is the failure of the script to complete in the allotted time that causes the alarm not to be shut off, and that's when you see "Alarm Call" on the screen.
You can find out what scripts did not complete by examining the "prc_sync" log file in /etc/rc0.d/messages and /etc/rc2.d/messages.
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