101.3 Change runlevels and shutdown or reboot system

Question 1

/etc/inittab

Answer 1

inittab is a configuration file, which describes which processes are started at bootup and during normal operation.

Sets the Default Run Level
Edit the file by using the VI editor

Question 2

Runlevel 0

Answer 2

Halt

Question 3

Runlevel 1

Answer 3

Single user mode (Recovery)

Question 4

Runlevel 2

Answer 4

Debian/Ubuntu Default

Question 5

Runlevel 3

Answer 5

Redhat Suse - Text mode

Question 6

Runlevel 4

Answer 6

Wildcard

Question 7

Runlevel 5

Answer 7

Redhat Suse - GUI mode (X Windows)

Question 8

Runlevel 6

Answer 8

Reboot

Question 9

/etc/inittab

Answer 9

“inittab file describes which processes are started at bootup and during normal operation
Sets the Default Run Level
Edit the file by using the VI editor”

Question 10

dmesg

Answer 10

is a command on most Linux and Unix based operating systems that prints the message buffer of the kernel.

Question 11

Set the default runlevel.

Answer 11

Edit the inittab (/etc/inittab) and change run level

Question 12

telinit

Answer 12

“A variant of init is telinit.
This program can take a runlevel number just like init to change to that runlevel, but it can also take the Q or q option to have the tool reread /etc/
inittab and implement any changes it finds there.
Thus, if you’ve made a change to the runlevel in /etc/inittab, you can immediately implement that change by typing telinit q.”

Question 13

init

Answer 13

init (short for initialization) is a daemon process that is the direct or indirect ancestor of all other processes.

It automatically adopts all orphaned processes.

Init is the first process started during booting, and is typically assigned PID number 1.

It is started by the kernel using a hard-coded filename, and if the kernel is unable to start it, a kernel panic will result.

Init continues running until the system is shut down.

Question 14

/etc/rcx.d (X is the number of the runlevel

Answer 14

Symbolic link back to the init.d

Question 15

Change between run levels including single user mode.

Answer 15

“init 1 (The simplest case is to have it change to the runlevel you specify. For instance, to change to runlevel 1)

”

Question 16

shutdown

Answer 16

“shutdown -k (warning)
shutdown -r (reboot)
shutdown -h (halt after shutdown)
shutdown -c (cancel shutdown)
shutdown time “

Question 17

/etc/init.d

Answer 17

“In each run-level you will find a series of if links pointing to start-up scripts located in /etc/init.d .
The names of these links all start as either K(kill) or S (start), followed by a number.”