init Flashcards
\init
initialization
The version of init that has been used in Linux systems is based off of the System V init system that was originally used in UNIX systems and a downside to the classic init system
is that services are started up 1 after the other. This was meant to keep things simple, but the problem arose when a particular service or function was not yet ready which could hang the system, preventing other services from starting.
sysvinit
after a Linux kernel loads up and it brings in the initial RAM disk, it then seeks out an initialization system to hand over control of the computer.
init system
The first place that the kernel looks for is and once this program is located, the kernel starts it so at this point, the init program is in control.
/sbin/init
read the configuration settings in /etc/inittab to determine what runlevel the system should be operating in.
first step of init
Linux standards base version 4.1 - basically just a predefined configuration that the computer will operate within. Each runlevel starts and/or stops scripts for various services depending on how the system should be set up. The system can only operate in 1 runlevel at a time.
runlevel
is the halt or shutdown level and is when init run scripts that stop services and powers off the system.
Runlevel 0
single user mode level typically in this setup, the root user is the only user allowed to log into the system as this level is primarily used for maintenance task and repair functionality.
Runlevel 1
is for multiple users to log in but without any network interfaces brought up nor are there any remote file systems mounted.
Runlevel 2
is the same as runlevel 2 except that networking is also available.Historically, most Linux servers were set up to run at this level by default.
Runlevel 3
is typically not used but it is available should an administrator want to set up a custom runlevel environment.
Runlevel 4
is the same as runlevel 3 but with a graphical desktop running as well. Older Linux workstations with desktop environments were set up to run in level 5 by default.
Runlevel 5
is the reboot runlevel. This is where init stops services and restarts the system, going back through the complete computer boot up sequence once again.
runlevel 6
group of fields divided by a colon
inittab file
identifier for this line. In the case of this example, we have ID as shorthand for init default.
inittab first field