Review Chapter 7, Linux Files and Processes, section: Terminating/Restarting Processes Using Scripts, and Chapter 3, Startup and Shutdown, “Initialization and Startup Scripts”, in Linux System Administration
Also see Mayank Sarup’s article at FreeOS.com
0 – Shutdown. Get here by running the command init 0.
1 – Single-user mode. init 1
2 – Multi-user, no networking mode. init 2
3 – Multi-user, with networking, command-line mode. init 3
4 – (Usually) unused mode. init 4
5 – Multi-user, with networking, X11 (GUI) mode. init 5
6 – Reboot mode. init 6
You can check your current runlevel, and the immediately preceding runlevel, with the runlevel command.
This file is /etc/inittab . cat or less this file, and note the Default Runlevel section.
See the line:
Do NOT set initdefault to 0 or 6!
In a terminal window, go to /etc/rc.d .
Run an ls command, then cat each of these:
rc – controls all movement between runlevels
rc.sysinit – runs once on system startup
rc.local – runs once, after everything else, on system startup
Change directories to /etc/init.d and run an ls command.
These are the actual scripts. Cat a few and notice how they handle multiple conditions (similarly to a class): start, stop, reload and status.
Change directories to /etc/rc3.d and run an ls command.
“K” scripts kill processes (services); “S” scripts start processes. The following number is a priority number.
This is a good time to learn about the ln command.
You can see the startup logging information (the “kernel ring buffer”) by running the command:
dmesg #or /bin/dmesg
You’ll see the information that scrolled past on the screen as your system booted.
To see information about the success or failure of startup scripts (the ones in /etc/rc.d/) look at the file /var/log/boot.log.
To see kernel and system messages, see the file /var/log/messages.
All system logs are rotated by the logrotate script, configured by the file /etc/logrotate.conf.
Finally, current information about the system is in the /proc (virtual) filesystem.
See these files in /proc/:
interrupts – IRQ info
cpuinfo – CPU info
dma – DMA info
ioports – I/O info
meminfo – Memory info: available, free, swap, cached
loadavg – System load avg
uptime – Time since boot
version – Kernel version
scsi – SCSI info, if any
ide – IDE info
net – Network info
sys – Kernel config parameters
|Runlevel and Shutdown Commands
|shutdown -h now
|shutdown -r now
|shutdown -h +5
|shutdown -r+5 “The system is going down in 5 minutes”