UNIX STRUCTURE

Linux Distributions • Debian GNU/Linux (Xandros, Knopix,...)

– a free operating system that provides almost 4000 software packages for six architectures (Intel, Motorola, Alpha, SPARC, PowerPC, ARM) and is developed entirely by volunteers over the Internet

• Fedora/RedHat – a Red-Hat-sponsored and community-supported open source project. The goal of The Fedora

Project is to work with the Linux community to build a complete, general purpose operating system exclusively from free software. Development will be done in a public forum

• Mandrake Linux – a friendly Linux Operating System which specializes in ease-of-use for both servers and the

home/office. It is freely available in many languages throughout the world • Slackware

– a long running Linux distribution that descends from the SLS Distribution • SuSE Linux

– an extremely popular distro that features excellent documentation, thousands of applications on a DVD/CD-ROM set

• Gentoo Linux – an optimized GNU/Linux distribution featuring 5 different pgcc-optimized builds, including Intel

Pentium, Pentium Pro/II/III and AMD K6 optimized

BSD Versions

• FreeBSD - Focusing on features and ease of use

• Darwin (OS X) - Focusing on the desktop and multimedia with use of the Apple's Aqua Interface

• NetBSD - Focusing on portability

• OpenBSD - Focusing on security

• PicoBSD - Focusing on size (extremely small)

• DragonflyBSD - Focusing on new computing paradigms

Citi brīvi pieejami Unix

• Solaris 10 – x64/x86

• % isainfo -v

• 64-bit amd64 applications

• 32-bit i386 applications

– SPARC

• Darwin

• Minix

UNIX

The layers of a UNIX system.

User Interface

Essential Unix Architecture Applications

System Libraries (libc)

System Call Interface

Hardware

Architecture-Dependent Code

I/O Related Process Related

Scheduler

Memory Management

IPC

File Systems

Networking

Device Drivers

Mo

du

les

Kernel services • Border between kernel level and user level code is supported by the

hardware protection • Kernel is working in completely isolated address range and it’s

impossible to get access to that address space from user level • Any interaction between user level code and kernel possible only by

means of system call, which are strictly controlled by the kernel • In most cases system calls are synchronous for user level application. • But it is possible that kernel will make some work sometimes after it

returns results to the user level. • In most cases system call is implemented by the means of hardware

exception, that change CPU working mode and current virtual memory content

• Kernel is controlling system call arguments very strictly before executing the system call.

• Every system call arguments will be copied to the kernel address space in order to garantee, that arguments will not be changed during the system call

• The addreses, where the result of the system call will be placed, have to be owned by the process, who called system call (checked)

• If system call got an error, it returns -1 and sets global errno variable.

System Calls

• System Calls for process control – fork() – wait() – execl(), execlp(), execv(), execvp() – exit() – signal(sig, handler) – kill(sig, pid)

• System calls for low level file I/O – creat(name, permissions) – open(name, mode) – close(fd) – unlink(fd) – read(fd, buffer, n_to_read) – write(fd, buffer, n_to_write) – lseek(fd, offest, whence)

• System Calls for IPC – pipe(fildes) – dup(fd)

• Total ~270 System Calls in Linux kernel v2.6 – Portable Operating System Interface

(POSIX) – ISO/IEC 9945 – IEEE 1003 – Single UNIX Specification (SUS) – Linux Standard Base

System Calls Extended information

System Calls for Memory Management

• s is an error code

• b and addr are memory addresses

• len is a length

• prot controls protection

• flags are miscellaneous bits

• fd is a file descriptor

• offset is a file offset

System Calls for File Management

• s is an error code

• fd is a file descriptor

• position is a file offset

System Calls for Directory Management

• s is an error code • dir identifies a directory stream • dirent is a directory entry

System Calls for File Protection

• s is an error code

• uid and gid are the UID and GID, respectively

System Calls for Process Management

s is an error code pid is a process ID residual is the remaining time from the previous alarm

Shell Basic Works

System Lifecycle: Ups & Downs

Power

on Power

off

Boot-

loader

Kernel

Init

OS

Init

RUN! Shut

down

httpd

lpd

Processes

/etc/init

kernel Process 0: Kernel bootstrap. Start process 1.

Process 1: create processes to allow login.

inetd

/etc/getty

fork

exec

/bin/login

exec

shell

exec

/etc/getty

fork

exec

/bin/login

exec

shell

exec

condition terminal for login

check password

command interpreter

kernal mode

user mode

Different Shells

• Bourne

• C Shell

• Korn Shell

• BASH Last login: Tue Sep 21 07:58:17 2004 from 81.198.226.108

[root@unix root]#

[root@unix root]# ps

PID TTY TIME CMD

20879 pts/7 00:00:00 bash

20905 pts/7 00:00:00 ps

[root@unix root]#

[root@unix root]# ls -l

total 64

-rw-r--r-- 1 root root 1204 Sep 20 16:11 anaconda-ks.cfg

-rw-r--r-- 1 root root 49872 Sep 20 16:11 install.log

-rw-r--r-- 1 root root 2306 Sep 20 16:11 install.log.syslog

[root@unix root]#

[root@unix root]# pwd

/root

[root@unix root]#

Illustration of Process Control Calls

The ls Command

Steps in executing the command ls type to the shell

UNIX Utility Programs

A few of the more common UNIX utility programs required by POSIX

Ieejot sistēmā, lietotājam automātiski tiek iestādītas dažas “environment variables”. Lai tos aplūkotu, jāizpilda komandu env. Piemēram:

• PWD=ceļš #kur atrodamies

• TZ=(EET) #laiku zona (East European Time)

• PAGER=(less, more) #lasītājs pēc noklusēšanas

• LOGNAME=vārds #lietotāja vārds

• HOME=/home/vārds #lietotāja mājas katalogs

• HOSTNAME=resursdators #resursdatora vārds

• LD_LIBRARY_PATH=:ceļš #dinamiskās bibliotēkas

• MANPATH=:ceļš #ceļš, kur meklējas “manual”

• ENV=/etc/bash_common #kur ir “environment variables”

• LESS=-fdeiMQw #atslēgas lasītājam pēc noklusēšanas

Environment variables.

• EDITOR=/usr/local/bin/joe #redaktors pēc noklusēšanas

• TERM=vt100 #termināla tipa uzstādīšana (lietotājam)

• PS1= \u@\h (\w) #aicinājuma formāts

• Machtype=mašīnas_tips #mašīnas tips (aparatūra)

• MAIL=ceļš #fails, kur noliek ieejošo pastu

• RHOST=hosta_adrese #kādā datorā mēs esam

• SHELL=ceļš #lietotāja komandinterpretators

• HOSTTYPE=hosta_tips # resursdatora tips

• OSTYPE=OS _tips #OS tips (solarisN.N, utl.)

• PATH=ceļš:jauns_ceļš #meklēšanas saraksts. Ar to palīdzību tiek meklēti izpildāmi faili

• LESSCHARSET=latin1 #attēlu kodētājs

• _=ceļš #kur atrodas atbilstošais fails (env)

Environment variables (Turpinājums).

Environment Variables

[root@unix /]# env

HOSTNAME=unix.mii.lu.lv

TERM=vt100

SHELL=/bin/bash

HISTSIZE=1000

SSH_CLIENT=::ffff:81.198.226.108 1289 22

SSH_TTY=/dev/pts/3

USER=root

LS_COLORS=no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:bd=40;33;01:cd=40;33;01:

USERNAME=root

MAIL=/var/spool/mail/root

PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin:/root/bin

INPUTRC=/etc/inputrc

PWD=/

LANG=en_US.UTF-8

SHLVL=1

HOME=/root

BASH_ENV=/root/.bashrc

LOGNAME=root

SSH_CONNECTION=::ffff:81.198.226.108 1289 ::ffff:159.148.108.245 22

LESSOPEN=|/usr/bin/lesspipe.sh %s

G_BROKEN_FILENAMES=1

_=/bin/env

OLDPWD=/sys

[root@unix /]#