Linux boots

Linux boots



ctrlaltdel

The ctrlaltdel action controls what the system does when you press CONTROL-ALT-DELETE
on a virtual console. On most systems, this is some sort of reboot command using the shutdown command.




The sysinit action is the very first thing that init should run when it starts up, before entering any runlevels.


How processes in runlevels start

You are now ready to learn how init starts the system services, just
before it lets you log in. Recall this inittab line from earlier:

l5:5:wait:/etc/rc.d/rc 5

This small line triggers many other programs. rc stands for run commands,
and you will hear people refer to the commands as scripts, programs, or services.
So, where are these commands, anyway?

For runlevel 5, in this example, the commands are probably either in /etc/rc.d/rc5.d or /etc/rc5.d.
Runlevel 1 uses rc1.d, runlevel 2 uses rc2.d, and so on. You might find the following items in the rc5.d directory:

S10sysklogd S20ppp S99gpm S12kerneld S25netstd_nfs S99httpd S15netstd_init S30netstd_misc S99rmnologin


S20acct S89atd

S20logoutd S89cron

The rc 5 command starts programs in this runlevel directory by running the following commands:

S10sysklogd start S12kerneld start S15netstd_init start S18netbase start ... S99sshd start

Notice the start argument in each command. The S in a command name means that the
command should run in start mode, and the number (00 through 99) determines
where in the sequence rc starts the command.

The rc*.d commands are usually shell scripts that start programs in /sbin or /usr/sbin.
Normally, you can figure out what one of the commands actually does
by looking at the script with less or another pager program.