[prog] check if script parent process is "init"

[Wolfgang Petzold]

Hello!

Dominik Schramm wrote:

> I'd like to check in a Bash script if it is being run by init,
> i.e. directly upon system startup, and not interactively
> or from another process -- say, cron.

The init process usually runs scripts in /etc/init.d/ (or a similar 
location) by calling symlinks in "runlevel directories", /etc/rc?.d/ in 
my (debian) case.

The scripts themselves can then tell by the name they were called with 
if they are run automatically or manually. See if you have some 
/etc/init.d/skeleton for an example.

Though this might be done in some not so obvious way, the principle is:

if my name is like /etc/init.d/rc?.d/S*
	I am to start, called automatically
else if my name is like /etc/init.d/rc?.d/K*
	I am to stop, called automatically
else
	I am called manually
	Check command line for what to do
fi

On the other hand, if I remember correctly what I once read about the 
boot process, the init process always has PID 1. So, if another (bash) 
process is started by init, bash should set its variable ${PPID} to 1 
accordingly.

Hope that helps,
Wolfgang