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developersguide:frompowerontologinprompt

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/!\ Slightly stale: informations about criticity, order, and numbers are out of date.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

developersguide/frompowerontologinprompt.txt · Last modified: 2014/11/11 08:52 (external edit)