init is a legacy unix and linux application generally responsabily of the process running in the system.
###Grand Unified Bootloader ####
1. BIOS ( Ensure hardware health) CPU (s), Memory, Hard Disk(s)
2. GRUB (Present menu to user and defaults to a selection within timer)
3. OS Kernel (Solaris / Linux / Windows / etc )
4. Sched – Pid 0
5. INIT
6. SMF
7. Operational Single / Multi-User System
### INIT in detail ####
init is represented in the process table as PID 1
which init
/usr/sbin/init
INIT’s config file is: /etc/inittab
init table ( reads inmediatly the inittab )
Supported Runlevels: 0 – S
0 – shutdown runlevel
1 – Single User Mode – No networking support is provided
2 – multi-user support without nfs
3 – multi-user support with NFS (Default Runleve)
4 – unused
5 – interactive boot
S – Single User Mode – No networking support is provided
###### /etc/inittab ############################################
id:run_state (0–6):how_to_run_process
(boot,bootwait,initdefault,off,once,powerfail,powerwait, sysinit,wait):what process to run
ap::sysinit:/sbin/autopush -f /etc/iu.ap
sp::sysinit:/sbin/soconfig -f /etc/sock2path
smf::sysinit:/lib/svc/bin/svc.startd >/dev/msglog 2<>/dev/msglog </dev/console
p3:s1234:powerfail:/usr/sbin/shutdown -y -i5 -g0 >/dev/msglog 2<>/dev/msglog