SGI IRIX bootup

The boot process of the IRIX operating system on SGI workstations is dependent upon your CPU type. If you don't know your CPU type, it will be apparent as the system boots.
This is a list of CPU types:

IP12,IP17
IP19,IP20,IP22
IP5,IP6,IP7,IP9

If your system is a CPU type IP12 or IP17, upon powering on or booting the message below will be displayed:

	Starting up the system...

To perform system maintenance instead, press <ESC>.

This message is displayed for five seconds before IRIX attempts to load.

If your system is a CPU type IP19,IP20 or IP22, upon powering on or booting the message below or something similar will be displayed:


System Maintenance Menu

1) Start System
2) Install System Software
3) Run Diagnostics
4) Recover System
5) Enter Command Monitor

Option?

Choose "Start System" to attempt to load IRIX.

If you system is a CPU type IP5,IP6,IP7 or IP9, upon powering on or booting the message below:

        Starting up the system...

Then a graphic menu is displayed for five seconds before IRIX attempts to load.

System Initialization

Once power to the computer and display monitor or console has been turned on, the computer runs power-on diagnostics, displays a copyright message and the system startup information mentioned above. A copy of the messages are also sent to the /var/adm/SYSLOG file.

The Command (PROM) Monitor specifies the name of the boot file which will be loaded and executed as well as the root (or boot) drive. The PROM (Programmable Read-Only Memory) chips are separate from the disk and the operating system. They are a low level interface for the system. If the ESCAPE key is pressed or the "Enter Command Monitor" is selected the system will halt the loading of IRIX. From the command monitor you may run extended diagnostic tests on the hardware and set variables that effect the loading of IRIX.

The boot file is normally sash, (standalone shell). sash is a device and filesystem aware version of the Command Monitor program. A copy of sash is placed in the volume header of the root disk when the system software is installed.

The sash program finds, loads and executes the /unix kernel file which is on the root disk. The kernel creates the init process which then consults the file /etc/inittab. The init process evaluates and possibly, depending on the run level specified, executes each line of the inittab file.

The inittab looks at each line in the file to decide which processes exist for each run level. For the multiuser mode (run level 2), init finds the entries that have the tag (also 2) for the run level and executes everything after the third colon on the line.

The system /etc/inittab looks something like this:

is:2:initdefault: 
fs::sysinit:/etc/bcheckrc </dev/console >/dev/console 2>&1 
mt::sysinit:/etc/brc </dev/console >/dev/console 2>&1
s0:06s:wait:/etc/rc0 >/dev/console 2>&1 </dev/console
s1:1:wait:/etc/shutdown -y -iS -g0 >/dev/console 2>&1 </dev/console
s2:23:wait:/etc/rc2 >/dev/console 2>&1 </dev/console 
s3:3:wait:/etc/rc3 >/dev/console 2>&1 </dev/console 
or:06:wait:/etc/umount -ak -b /proc,/debug /dev/console 2>&1
of:0:wait:/etc/uadmin 2 0 >/dev/console 2>&1 </dev/console 
RB:6:wait:echo "The system is being restarted.