Introduction to LinuxUNIX

1
Introduction toLinux/UNIX
2
History

• UNIX beginnings in 1969 (Linus Torvalds is born!)
• AT T Bell Laboratories
• Ken Thompson and Dennis Richie
• Working version (in 1970) on a DEC PDP 11/70
• UNIX and C Relationship
• June 81 Berkeley UNIX 4.1 BSD (enhanced with vi,
  csh, and virtual memory management)
• 1983 Berkeley UNIX 4.2 BSD (added TCP/IP
  networking, sockets and a new file system)
• Later ? UNIX/32V, SYSTEM III, SYSTEM V
• and ? ? Linux is introduced by Linus B. Torvalds
  in 1991
• 1994 -- RedHat Linux is introduced

3
GNU Project

• Launched in 1984 to develop a complete UNIX
  Operating system that is free software
• www.gnu.org
• Organized by free software foundation
• Free GNU Software http//directory.fsf.org/GNU/
• Usually C code, but some C
• GNU has a 72-page document of coding standards
  well-written code
• POSIX Portable Operating System Interface
• An IEEE standard which describes the behaviour of
  UNIX and UNIX-like operating systems.
• POSIX support assures code portability between
  systems and is increasingly mandated for
  commercial applications and government contracts

4
Basics

• Talking to Linux/UNIX ? The Shell
• displays the prompt for your next command and
  parses your command input and executes it
• several different kinds Bourne Shell or sh, ksh,
  csh, and tcsh
• Login shell
• A sample .bashrc http//web.umr.edu/ercal/284/
  .bashrc
• A sample .bash_login http//web.umr.edu/ercal/2
  84/.bash_login
• A sample .login http//web.umr.edu/ercal/284/.
  login
• A sample .userlogin http//web.umr.edu/ercal/28
  4/.userlogin
• A sample .cshrc http//web.umr.edu/ercal/284/.
  cshrc
• A sample .usercshrc http//web.umr.edu/ercal/2
  84/.usercshrc
• A sample .alias http//web.umr.edu/ercal/284/.
  alias
• Home directory
• /afs/umr.edu/users/YourLoginName or
• YourLoginName (e.g. ercal sea)
• File/Directory structure ? A tree

5
here Useful UNIX/Linux Commands

• http//web.umr.edu/ercal/284/UNIX-commands.txt
• A subset of these commands are
• alias/unalias, bg, cat, cc, cd, chmod, cp, csh,
  diff, du echo, emacs, fg, gcc, grep, history,
  jobs, kill, ln logout, lpq, lpr, lprm, ls, man,
  mkdir, more, mv, printenv, ps, pwd, rlogin, rm,
  rmdir, rsh, script, set, setenv, source tail,
  tar, telnet, touch, unset unsetenv uudecode,
  uuencode, vacation, vi, wc, which, xterm

6
More Basics

• Access Control
• cd ls l and chmod commands
• rwx rwx rwx ? 7 7 7 rwx r_x r_x ? 7
  5 5
• Consulting the on-line manual ? man command
• Compiling with gcc and g
• I/O Redirection
• gt Redirect output
• lt Redirect input
• p Run p in the background (try also jobs,
  Z, bg, fg, ps, and kill)
• p1 p2 Pipe output of p1 as input for p2
• p gtgt f Append output of p into file f

7
Command-line arguments

• dell2gt cat filename.c
• int main( int argc, char argv)

argc 2
argv
cat \0
0
1
filename.c \0
NULL
2
8
Text Editing / e-mail / data compression

• vi (/usr/bin/vim)
• GNU emacs (/usr/bin/emacs)
• Electronic Mail /usr/bin/mutt
• /bin/gzip /bin/gunzip

9
Writing Simple Shell Scripts

• Bourne Shell Programming (bash standard Linux
  shell)
• http//steve-parker.org/sh/sh.shtml
• http//www-106.ibm.com/developerworks/linux/librar
  y/l-bash.html
• http//www-106.ibm.com/developerworks/linux/librar
  y/l-bash2.html
• Example http//web.umr.edu/ercal/284/ShellScript
  s/args
• !/usr/bin/env bash
• echo name of script is 0
• echo first argument is 1
• echo second argument is 2
• echo third argument is 3
• echo eleventh argument is 11
• echo number of arguments is

10
More examples

• http//web.umr.edu/ercal/284/ShellScripts/SampleS
  cripts.html
• Example 1 Remove "Cntl-M" from a given file
• Example 2 Keep track of users every 20 seconds
  - ( problem with while )
• Example 3 List all files in all subdirectories
  recursively
• Example 4 List and count all files in all
  subdirectories
• Example 5 Find the path(s) to a file recursively

11
Linux/UNIX Process Model

• Process Attributes
• A unique process identifier (PID) - getpid()
  call
• parent process (PPID) getppid() call
• permission identifiers (UID, GID etc.)
• An address space
• A current working directory (.)
• A set of open files, directories
• environment variables env or printenv (e.g.
  PATH . HOME)
• scheduling priority

12
Linux/UNIX Processes

• ps acefl more
• ps acefl grep init
• the first, primordial process ? init PID1
  PPID0 (kernel)
• All other processes are descendants of init.
• Each process has only one parent but could have
  many children
• Child processes inherit the environment of the
  parent process
• All programs start with three files open stdin,
  stdout, stderr

13
make facility

• used for maintaining component modules in a
  software system.
• The default file for make is called makefile or
  Makefile.
• Otherwise, use
• make f filename
• A makefile consists of a series of sections each
  composed of target, dependencies and commands.
• Example http//web.umr.edu/price/cs328/makeI
• Every command line must begin with a tab.
• make target returns without doing anything if no
  changes are made to any of the files involved in
  making the target.

14
makefile

• A simple Makefile example
• default all
• all driver
• driver program.o \
• scanner.o
• _at_echo "Building _at_"
• g program.o scanner.o -o driver
• program.o parser.h symbol.h \
• program.cpp
• g -c program.cpp
• scanner.o scanner.h \
• scanner.cpp
• g -c scanner.cpp