Introduction to UNIX Operating System

1
Introduction to UNIX Operating System
2

• Unix
• Unix (officially trademarked as UNIX, sometimes
  also written as Unix with small caps) is a
  computer operating system originally developed in
  1969 by a group of ATT employees at Bell Labs,
  including Ken Thompson, Dennis Ritchie, Douglas
  McIlroy, and Joe Ossanna. Today's Unix systems
  are split into various branches, developed over
  time by ATT as well as various commercial
  vendors and non-profit organizations.
• As of 2007, the owner of the trademark is The
  Open Group, an industry standards consortium.
  Only systems fully compliant with and certified
  to the Single UNIX Specification are qualified to
  use the trademark others are called "Unix
  system-like" or "Unix-like".
• During the late 1970s and early 1980s, the
  influence of Unix in academic circles led to
  large-scale adoption of Unix (particularly of the
  BSD (Berkeley Software Distribution ) variant,
  originating from the University of California,
  Berkeley) by commercial startups, the most
  notable of which are Solaris, HP-UX, and AIX.
  Today, in addition to certified Unix systems,
  Unix-like operating systems such as Linux and BSD
  are commonly encountered. Sometimes, "traditional
  Unix" may be used to describe a Unix or an
  operating system that has the characteristics of
  either Version 7 Unix or UNIX System V.

3
UNIX commands

• Misc commands
• man,banner,cal, calendar,clear,nohup, tty .
• Man ual command.
• man man This is help command, and will explains
  you about online manual pages you can also use
  man
• in conjunction with any command to learn more
  about that command for example.
• man ls will explain about the ls command and how
  you can use it.
• man -k pattern command will search for the
  pattern in given command.
• --------------------------------------------------
  ------------------------------
• Banner command.
• banner prints characters in a sort of ascii art
  poster, for example to print wait in big letters.
  I will type
• banner wait at unix command line or in my script.
  This is how it will look.

4
UNIX commands

• Cal command
• cal command will print the calander on current
  month by default. If you want to print calander
  of august of 1965. That's eightht month of 1965.
• cal 8 1965 will print following results.
• August 1965
• S M Tu W Th F S
• 1 2 3 4 5 6 7
• 8 9 10 11 12 13 14
• 15 16 17 18 19 20 21
• 22 23 24 25 26 27 28
• 29 30 31
• --------------------------------------------------
  ------------------------------
• Clear command
• clear command clears the screen and puts cursor
  at beginning of first line.

5
UNIX commands

• Tty command
• Tty command will display your terminal. Syntax is
• tty options
• Options
• -l will print the synchronous line number.
• -s will return only the codes 0 (a terminal), 1
  (not a terminal), 2 (invalid options) (good for
  scripts)

6

• File Management commands.
• cat,cd, cp, file,head,tail, ln,ls,mkdir ,more,mv,
  pwd, rcp,rm, rmdir, wc.
• --------------------------------------------------
  ------------------------------
• Pwd command.
• pwd command will print your home directory on
  screen, pwd means print working directory.
• /u0/ssb/sandeep
• is output for the command when I use pwd in
  /u0/ssb/sandeep directory.
• --------------------------------------------------
  ------------------------------
• Ls command
• ls command is most widely used command and it
  displays the contents of directory.
• options
• ls will list all the files in your home
  directory, this command has many options.

7

• Cp command.
• cp command copies a file. If I want to copy a
  file named oldfile in a current directory to a
  file named newfile in a current directory.
• cp oldfile newfile
• If I want to copy oldfile to other directory for
  example /tmp then
• cp oldfile /tmp/newfile. Useful options available
  with cp are -p and -r . -p options preserves the
  modification time and permissions, -r recursively
  copy a directory and its files, duplicating the
  tree structure.
• --------------------------------------------------
  ------------------------------
• Rcp command.
• rcp command will copy files between two unix
  systems and works just like cp command (-p and -i
  options too).
• For example you are on a unix system that is
  called Cheetah and want to copy a file which is
  in current directory to a system that is called
  lion in /usr/john/ directory then you can use rcp
  command
• rcp filename lion/usr/john
• You will also need permissions between the two
  machines. For more infor type man rcp at command
  line.
• --------------------------------------------------
  ------------------------------
• Mv command.

8

• Head command.
• head filename by default will display the first
  10 lines of a file.
• If you want first 50 lines you can use head -50
  filename or for 37 lines head -37 filename and so
  forth.
• --------------------------------------------------
  ------------------------------
• Tail command.
• tail filename by default will display the last 10
  lines of a file.
• If you want last 50 lines then you can use tail
  -50 filename.
• --------------------------------------------------
  ------------------------------
• More command. more command will display a page at
  a time and then wait for input which is spacebar.
  For example if you have a file which is 500 lines
  and you want to read it all. So you can use
• more filename

9

• Rmdir command. rmdir command will remove
  directory or directories if a directory is empty.
  
• Options
• rm -r directory_name will remove all files even
  if directory is not empty.
• rmdir sandeep is how you use it to remove sandeep
  directory.
• rmdir -p will remove directories and any parent
  directories that are empty.
• rmdir -s will suppress standard error messages
  caused by -p.

10

• Comparison and Searching
• diff,dircmp, cmp, grep, find.
• Diff command. diff command will compare the two
  files and print out the differences between.
  Here I have two ascii text files. fileone and
  file two. Contents of fileone are
• This is first file
• this is second line
• this is third line
• this is different aslkdjf
• this is not differentfiletwo contains
• This is first file
• this is second line
• this is third line
• this is different xxxxxxxaslkdjf
• this is not differentdiff fileone filetwo will
  give following output
• 4c4 lt this is different aslkdjf --- gt this is
  different xxxxxxxaslkdjf
• Cmp command. cmp command compares the two files.
  For example I have two different files fileone
  and filetwo. cmp fileone filetwo will give me
• fileone filetwo differ char 80, line 4 if I run
  cmp command on similar files nothing is
  returned.-s command can be used to return exit
  codes. i.e. return 0 if files are identical, 1 if
  files are different, 2 if files are inaccessible.
  This following command prints a message 'no
  changes' if files are same cmp -s fileone file1
  echo 'no changes' . no changes
• Dircmp Command. dircmp command compares two
  directories. If i have two directories in my home
  directory nameddirone and dirtwo and each has
  5-10 files in it. Then dircmp dirone dirtwo will
  return this
• Dec 9 1606 1997 dirone only and dirtwo only Page
  1
• ./cal.txt

11

• Grep Command
• grep command is the most useful search command.
  You can use it to find processes running on
  system, to find a pattern in a file, etc. It can
  be used to search one or more files to match an
  expression.
• It can also be used in conjunction with other
  commands as in this following example, output of
  ps command is passed to grep command, here it
  means search all processes in system and find the
  pattern sleep.
• ps -ef grep sleep will display all the sleep
  processes running in the system as follows.
• ops 12964 25853 0 161224 ttyAE/AAES 000
  sleep 60
• dxi 12974 15640 0 161225 ttyAH/AAHP 000
  sleep 60
• ops 12941 25688 0 161221 ttyAE/AAEt 000
  sleep 60
• ops 12847 25812 0 161159 ttyAH/AAH6 000
  sleep 60
• ops 12894 25834 0 161212 ttyAE/AAEX 000
  sleep 60
• dxi 13067 27253 2 161248 ttyAE/ABEY 000
  sleep 1
• ops 13046 25761 0 161244 ttyAE/AAE0 000
  sleep 60
• dxi 12956 13078 0 161223 ttyAG/AAG 000
  sleep 60
• ops 12965 25737 0 161224 ttyAE/AAEp 000
  sleep 60
• ops 12989 25778 0 161228 ttyAH/AAHv 000
  sleep 60
• ssb 13069 26758 2 161249 ttyAH/AAHs 000
  grep sleep
• pjk 27049 3353 0 152023 ? 000
  sleep 3600
• Options
• -b option will precede each line with its block
  number.

12

• Find command.
• Find command is a extremely useful command. you
  can search for any file anywhere using this
  command provided that file and directory you are
  searching has read write attributes set to you
  ,your, group or all. Find descends directory tree
  beginning at each pathname and finds the files
  that meet the specified conditions. Here are some
  examples.
• Some Examples
• find HOME -print will lists all files in your
  home directory.
• find /work -name chapter1 -print will list all
  files named chapter1 in /work directory.
• find / -type d -name 'man' -print will list all
  manpage directories.
• find / -size 0 -ok rm \ will remove all empty
  files on system.
• conditions of find
• -atime n -n n will find files that were last
  accessed more than n or less than -n days or n
  days.
• -ctime n or -n will find that were changed n -n
  or n days ago.
• -depth descend the directory structure, working
  on actual files first and then directories. You
  can use it with cpio command.
• -exec commad \ run the Unix command on each
  file matched by find. Very useful condition.
• -print print or list to standard output (screen).
  
• -name pattern find the pattern.
• -perm nnnfind files whole permission flags match
  octal number nnn.
• -size n find files that contain n blocks.

13

• Text processing
• cut,paste, sort, uniq,awk,sed,vi.
• --------------------------------------------------
  ------------------------------
• Cut command.
• cut command selects a list of columns or fields
  from one or more files.
• Option -c is for columns and -f for fields. It is
  entered as
• cut options files
• for example if a file named testfile contains
• this is firstline
• this is secondline
• this is thirdline
• Examples
• cut -c1,4 testfile will print this to standard
  output (screen)
• ts
• ts

14

• Sort command.
• sort command sort the lines of a file or files,
  in alphabetical order. for example if you have a
  file named testfile with these contents
• zzz
• aaa
• 1234
• yuer
• wer
• qww
• wwe
• Then running
• sort testfile
• will give us output of
• 1234
• aaa
• qww
• wer
• wwe

15

• Vi editor.
• vi command launches a vi sual editor. To edit a
  file type
• vi filename
• vi editor is a default editor of all Unix
  systems. It has several modes. In order to write
  characters you will need to hit i to be in insert
  mode and then start typing. Make sure that your
  terminal has correct settings, vt100 emulation
  works good if you are logged in using pc.
• Once you are done typing then to be in command
  mode where you can write/search/ you need to hit
  w filename to write
• and in case you are done writing and want to exit
  
• w! will write and exit.
• options
• i for insert mode.
• I inserts text at the curson
• A appends text at the end of the line.
• a appends text after cursor.
• O open a new line of text above the curson.
• o open a new line of text below the curson.
• for command mode.
• ltescapegt to invoke command mode from insert mode.
  
• !sh to run unix commands.

16

• Shell and programming
• Shell programming,bourne shell, ksh, csh,
  echo,line,sleep, test,cc compiler.
• --------------------------------------------------
  ------------------------------
• Shell programming concepts and commands.
• Shell programming is integral part of Unix
  operating systems. Shell is command line
  userinterface to Unix operating system, User have
  an option of picking an interface on Unix such as
  ksh, csh, or default sh., these are called
  shells(interface). Shell programming is used to
  automate many tasks. Shell programming is not a
  programming language in the truest sense of word
  since it is not compiled but rather an
  interpreted language. Unix was written in C
  language and thus c language is integral part of
  unix and available on all versions. Shells, like
  ksh and csh are popular shells on unix although
  there are 5 or 6 different shells available but I
  will only be discussing ksh and csh as well as
  sh. Common features among all shells are job
  control, for example if I am running a processes
  which is searching the whole system for .Z files
  and output is directed to a file named
  compressedfiles.
• example
• find / -name .Z -print gt compressedfiles
• then after entering this command hitting
• ltcontrol zgt
• key will suspend this job, then entering
• bg
• at command line will put this job in background,
  entering
• fg
• will put this job in foreground. Entering
• jobs
• at command line will show me all my concurrent
  jobs that are running.

17

• Bourne Shell (sh shell).
• sh or Bourne shell is default shell of Unix
  operating systems and is the most simplest shell
  in Unix systems.
• Examples
• cd ls execute one after another.
• (datewhopwd)gt logifile will redirect all the
  output from three commands to a filenamed
  logfile.
• sort file lp will first sort a file and then
  print it.
• alias options name'command' will let you
  create your own commands. i.e.
• alias ll"ls -la" will execute ls -la command
  whenever ll is entered.
• let expressions is syntax of let statement.
• let ii1 will work as a counter with i
  incrementing each time this statement is
  encountered.
• for xin list do commands done is syntax for for
  do loop.
• function name commands is the syntax of a
  function which can be called from anywhere in
  program.
• if condition1 then commands1 elif condition2 then
  commands2 ... ... ... else commands3 fi
• --------------------------------------------------
  ------------------------------
• Ksh shell (Korn).
• Ksh or Korn shell is widely used shell.

18

• Cu command.
• cu command is used for communications over a
  modem or direct line with another Unix system.
• Syntax is
• cu options destination
• Options
• -bn process lines using n-bit characters (7 or
  8).
• -cname Search UUCP's device file and select local
  area network that matches name.
• -d Prints diagnostics.
• -e sends even parity data to remote system
• -lline communicate on this device
  (line/dev/tty001, etc)
• -n prompts for a telephone number.
• -sn set transmission rate to n(e.g
  1200,2400,9600, BPS)
• Destination
• telno is the telephone number of the modem to
  connect to.
• system is call the system known to uucp.
• aadr is an address specific to LAN.
• --------------------------------------------------
  ------------------------------

19

• Login command.
• login command invokes a login session to a Unix
  system, which then authenticates the login to a
  system. System prompts you to enter userid and
  password.
• --------------------------------------------------
  ------------------------------
• Rlogin command.
• rlogin command is used to log on to remote Unix
  systems, user must have permissions on both
  systems as well as same userid, or an id defined
  in .rhosts file. Syntax is
• rlogin options host
• options
• -8 will allow 8 bit data to pass, instead of
  7-bit data.
• -e c will let you use escape character c.
• -l user will let you to login as user to remote
  host, instead of same as local host.
• --------------------------------------------------
  ------------------------------
• Talk command.
• talk command is used to invoke talk program
  available on all unix system which lets two users
  exchange information back and forth in real time.
  Syntax is

20

• Storage commands
• Compress command.
• Compress command compresses a file and returns
  the original file with .z extension, to
  uncompress this filename.Z file use uncompress
  filename command. syntax for compress command is
• compress options files
• Options
• -bn limit the number of bits in coding to n.
• -c write to standard output (do not change
  files).
• -f compress conditionally, do not prompt before
  overwriting files.
• -v Print the resulting percentage of reduction
  for files.
• --------------------------------------------------
  ------------------------------
• Uncompress command.
• Uncompress file uncompresses a file and return it
  to its original form.
• syntax is
• uncompress filename.Z this uncompresses the
  compressed file to its original name.
• Options

21

• Dump command is useful to backup the file
  systems.
• dump command copies all the files in filesystem
  that have been changed after a certain date. It
  is good for incremental backups. This information
  about date is derived from /var/adm/dumpdates and
  /etc/fstab .
• syntax for HP-UX dump is
• /usr/sbin/dump option argument ... filesystem
  
• Options
• 0-9 This number is dump level. 0 option causes
  entire filesystem to be dumped.
• b blocking factor taken into argument.
• d density of tape default value is 1600.
• f place the dump on next argument file instead of
  tape.
• This example causes the entire file system (/mnt)
  to be dumped on /dev/rmt/c0t0d0BEST and specifies
  that the density of the tape is 6250 BPI.
• /usr/sbin/dump 0df 6250 /dev/rmt/c0t0d0BEST /mnt
• for more info type man dump at command line.
• --------------------------------------------------
  ------------------------------
• Pack command.
• pack command compacts each file and combine them
  together into a filename.z file. The original
  file is replaced. Pcat and unpack will restore
  packed files to their original form.

22

• Tar command.
• tar command creates an archive of files into a
  single file.
• Tar copies and restore files to a tape or any
  storage media. Synopsis of tar is
• tar options file
• Examples
• tar cvf /dev/rmt/0 /bin /usr/bin creates an
  archive of /bin and /usr/bin, and store on the
  tape in /dev/rmt0.
• tar tvf /dev/rmt0 will list the tape's content in
  a /dev/rmt0 drive.
• tar cvf - 'find . -print' gt backup.tar will
  creates an archive of current directory and store
  it in file backup.tar.
• Functions
• c creates a new tape.
• r append files to a tape.
• t print the names of files if they are stored on
  the tape.
• x extract files from tape.
• Options
• b n use blocking factor of n.
• l print error messages about links not found.
• L follow symbolic links.

23

• System Status
• Chmod command.
• chmod command is used to change permissions on a
  file.
• for example if I have a text file with calender
  in it called cal.txt.
• initially when this file will be created the
  permissions for this file depends upon umask set
  in your profile files. As you can see this file
  has 666 or -rw-rw-rw attributes.
• ls -la cal.txt
• -rw-rw-rw- 1 ssb dxidev 135 Dec 3
  1614 cal.txt
• In this line above I have -rw-rw-rw- meaning
  respectively that owner can read and write file,
  member of the owner's group can read and write
  this file and anyone else connected to this
  system can read and write this file., next ssb is
  owner of this file dxidev is the group of this
  file, there are 135 bytes in this file, this file
  was created on December 3 at time1614 and at the
  end there is name of this file. Learn to read
  these permissions in binary, like this for
  example Decimal 644 which is 110 100 100 in
  binary meand rw-r--r-- or user can read,write
  this file, group can read only, everyone else can
  read only. Similarly, if permissions are 755 or
  111 101 101 that means rwxr-xr-x or user can
  read, write and execute, group can read and
  execute, everyone else can read and execute. All
  directories have d in front of permissions. So if
  you don't want anyone to see your files or to do
  anything with it use chmod command and make
  permissions so that only you can read and write
  to that file, i.e.
• chmod 600 filename.

24

• Chgrp command.
• chgrp command is used to change the group of a
  file or directory.
• You must own the file or be a superuser.
• chgrp options newgroup files is syntax of
  chgrp.
• Newgroup is either a group Id or a group name
  located in /etc/group .
• Options
• -h will change the group on symbolic links.
• -R recursively descend through directory changing
  group of all files and subdirectories.
• Crontab command.
• crontab command is used to schedule jobs. You
  must have permission to run this command by unix
  Administrator. Jobs are scheduled in five
  numbers, as follows.
• Minutes 0-59
• Hour 0-23
• Day of month 1-31
• month 1-12
• Day of week 0-6 (0 is sunday)

25

• Df command.
• df command displays information about mounted
  filesystems. It reports the number of free disk
  blocks. Typically a Disk block is 512 bytes (or
  1/2 Kilobyte).
• syntax is
• df options name
• Options
• -b will print only the number of free blocks.
• -e will print only the number of free files.
• -f will report free blocks but not free inodes.
• -F type will report on an umounted file system
  specified by type.
• -k will print allocation in kilobytes.
• -l will report only on local file systems.
• -n will print only the file system name type,
  with no arguments it lists type of all file
  systems

26

• Who command
• who command displays information about the
  current status of system.
• who options file
• Who as default prints login names of users
  currently logged in.
• Options
• -a use all options.
• -b Report information about last reboot.
• -d report expired processes.
• -H print headings.
• -p report previously spawned processes.
• -u report terminal usage.