Boot Process in Debian / Ubuntu
Boot up phases
There are 4 phases to starting up the system:
- BIOS
- Boot loader
- Kernel
- Upstart (which manages system tasks and services )
Kernel modules are loaded during the Kernel phase. The kernel uses a file system which is present in memory, called an 'initrd' for 'initial ram disk'. The kernel launches the init script inside the initrd file system, which loads hardware drivers and finds the root partition.
Upstart is the initialization scripts that run. These scripts involve different /etc/rc scripts and upstart events.
The old init system was replaced by the new "upstart" system.
init / runlevel
The runlevel 5 makes the sytem boot to the graphical xwindows, while the runlevel 3 boots to text console.
To change the default runlevel, use your favorite text editor on /etc/init/rc-sysinit.conf
vi /etc/init/rc-sysinit.conf
To see the current (and previous) runlevel:
runlevel
To switch runlevels:
init $runlevel
To reboot
init 6
To change the default runlevel, use your favorite text editor on /etc/init/rc-sysinit.conf...
sudo vim /etc/init/rc-sysinit.conf
Change this line to whichever runlevel you want...
env DEFAULT_RUNLEVEL=5
If Ubuntu were compliant with UNIX and Linux standard, adding '3' to grub's 'kernel' command in /boot/grub/menu.lst should be sufficient, because runlevel '3' means no 'X11' according to this standard.
