From power-on to the login prompt

Boot monitor

When the power is turned on, the typical PC will try to read the first sector from the BIOS's boot device, such as the first floppy disk or the first hard disk, into memory, and execute it. The code obtained from the hard disk (from the so-called master boot sector) immediately will replace itself by the code found in the first sector of the active partition. Thus, the PC now is executing the bootstrap code found in the first sector of /dev/fd0, /dev/c0d0p0, /dev/c0d0p1, /dev/c0d0p2, or /dev/c0d0p3 (assuming the boot disk is attached to controller 0).

In Minix's case, that bootstrap code loads the NetBSD boot loader, a multiboot-compliant boot loader that is able to boot Minix. The multiboot protocol loads the kernel and executables of boot-time processes (modules) somewhere in memory, according to the configuration settings and the commands entered.

System image

/!\ Slightly stale: informations about criticity, order, and numbers are out of date.

The MINIX 3 system is made up of the union of several independent programs:

Package

Source

Resiliency

Comments

Kernel

src/kernel

Critical

Process Manager server

src/servers/pm

Critical

Should be number 0 (just after kernel), API calls assume it.

Virtual File System server

src/servers/vfs

Critical

Should be number 1, API calls assume it.

Resurrection Service

src/servers/rs

Critical

src/drivers/memory

unknown

src/drivers/tty

unknown

src/servers/ds

unknown

Minix File System service

src/servers/mfs

Fail-safe

For the root file system on /dev/imgrd

Virtual Memory manager

src/servers/vm

Critical

Should be number 8, mmap*() API calls assume it.

src/servers/pfs

unknown

Init process

src/servers/init

unknown

Critical above means that a panic() inside that server will bring the whole system down. Fail-safe, on the other hand, means that MINIX 3 should be able to handle a failure of that server, usually by re-starting the driver.

System initialization, 'rc' scripts

The MINIX 3 system is running now, the different tasks initialize themselves. rs is the parent of all MINIX 3 system processes, while init is the grandparent of all user processes; note that the word user is used here in constrast to system processes; and, does not refer to the user-mode - kernel-mode distinction (all processes are user-mode in MINIX). A small file system, contained in RAM inside the 'memory' driver, is mounted as /. init is responsible for starting login processes on each terminal; but first, it runs /etc/rc, a shell script.

Image ramdisk

The ramdisk itself is build within the src/drivers/ramdisk directory.

The image ramdisk contains several drivers which are used to boot the system fully:

Package

Source

On ramdisk

Comments

at_wini

src/drivers/at_wini

bin/at_wini

bios_wini

src/drivers/bios_wini

bin/bios_wini

floppy

src/drivers/floppy

bin/floppy

pci

src/drivers/pci

bin/pci

Usually needed by the at_wini driver

Minix File System service

src/servers/mfs

sbin/mfs

For the real root file system

Ext2 File System service

src/servers/ext2

sbin/ext2

If real root is using EXT2 (Linux)

It also needs several commands, to perform the initialization,

Package

Source

On ramdisk

Comments

cdprobe

src/commands/cdprobe/cdprobe.c

bin/cdprobe

loadramdisk

src/commands/simple/loadramdisk.c

bin/loadramdisk

ash

src/commands/ash/*

bin/sh

service

src/servers/rs/service.c

bin/service

sysenv

src/commands/simple/sysenv.c

bin/sysenv

and several support files

Package

Source

On ramdisk

Comments

Access Control List

src/etc/system.conf

etc/system.conf

src/etc/mtab

etc/mtab

Empty file

src/etc/passwd

etc/passwd

Needed for running service

src/drivers/memory/ramdisk/rc

etc/rc

Actual instructions

Root file system initialization

/etc/rc checks the state of the system, and starts some daemons. It sets the system timezone if needed, the keyboard translation to the mapping in /etc/keymap if present, followed by a call to readclock(8) to set MINIX 3's time from the hardware clock. Next, the file systems are checked if necessary, and the /usr file system is mounted.

Multiuser initialization

The system now is ready for multi-user start-up. /etc/rc calls /usr/etc/rc. That cleans out /tmp/ and /usr/tmp/, and resets or cycles log files (by running /usr/etc/daily), starts the update(8) and cron(8) daemons, and initializes the network services.

/usr/etc/rc runs any scripts that might have been installed into /usr/local/etc/rc.d/ by packages.
Finally, /etc/rc runs /usr/local/etc/rc to initialize the system in a site- or host-dependent way.

Init

Init reads /etc/ttytab, and starts a getty(8) for each enabled terminal line, in order to allow a user to log in. Getty asks for a user-name, checks a password with login(1), changes to the user's home directory, and spawns a shell, as specified according to the `/etc/passwd`(5) file.

Shell

The shell is a command interpreter, which is a waiting process. Then the waiting process interprets and executes what the user typed. Programs that the user may run are stored by the file system. Execution of a program is accomplished by forking a child process. Then the child can access the system calls. After returning from the system call and ending of the child process the shell waits user input.

The shell starts by interpreting the /etc/profile and $HOME/.profile scripts, which sre used to set up respectively the system and user default values and parameters. On MINIX, $HOME/.profile also executes the instructions from $HOME/.ashrc.

MinixWiki: DevelopersGuide/FromPowerOnToLoginPrompt (last edited 2014-09-24 12:51:40 by David van Moolenbroek)