System Administration Introduction to Unix Session 2

1
System AdministrationIntroduction to
UnixSession 2 Fri 02 Nov 2007

• Reference
• chapter 1, The Unix Programming Environment,
  Kernighan Pike, ISBN 0-13-937681-X
• Albert Lingelbach, Jr.alingelb_at_yahoo.com

2
History of Unix

• Begun in 1969 at Bell Labs
• Timesharing / MultiuserOne computer, many
  terminals
• Programming
• Typesetting
• Group Communication

3
Architecture

• Kernel
• Windowing System
• Gnome
• Shell
• Programs

4
The shell environment

• tty (teletype) / terminal
• text only
• 24 lines, 80 columns
• default shell Bourne shell
• to open a tty right-click on desktop, choose
  Open Terminal
• echo
• print text to the tty
• try echo Hello
• what shell is running ?echo 0

5
Simple commands

• bash
• compatible with sh, added features
• command history with up arrow
• editable command line
• backspace (vs. delete)?
• date
• system date and time
• who
• what users are on the system

6
Flow Control characters

• ctrl-C
• stop a running command
• try troff
• ctrl-S / ctrl-Q
• pause/unpause output
• try countdown 1000
• end input
• ctrl-D

7
Command Arguments / Parameters

• mis-typed command
• gold not found
• command arguments / parameters
• try who am i
• try gold coins

8
User Communication

• news
• get local system news (written by the system
  administrator)?
• try news
• write
• write messages to another user on the system
  like IM but local
• try
• pair off
• using who, find userid of your partner
• write userid(and your partner does
  same)exchange messages

9
Manual Pages

• You have seen the following commands
• date
• who
• news
• write
• sh
• bash
• How to find more about them ?
• command -?often returns a short command synopsis
• man commandreturns the complete manual page
  reference for the command

10
Files

• As in any computer system, data is stored in
  files
• Most Unix files are (ASCII) text
• Many Unix commands manipulate text files

11
File Naming

• case sensitive
• spaces are problematic
• dot and underscore are useful separators

12
File Commands 1

• current (working) directory
• pwd
• print the working directory
• ls
• list the files in the working directory
• cd path
• change the working directory

13
File Paths 1

• filenames without a path default to the current
  directory
• example myfile.txt
• / is the root or top of the file system tree
• a file path contains directories separated by
  /(not \ as in DOS/windows)?
• example /home/export/staff/alingelb/file.txt

14
File Paths 2

• relative paths (not starting with /) start at
  the current directory
• current directory (.)?
• parent directory (..)?
• relative to any preceding directory
• examples
• ./file.txt (the same as file.txt)?
• ../../student/kate/file.txt
• in general, any command that takes a file as an
  argument, will accept a path file (path/file)?

15
File Commands - 2

• touch filename
• create an empty file
• example touch myfile.txt
• rm filename
• delete a file (forever be careful!)?
• example rm myfile.txt
• cp original_file new_file
• copy a file
• example cp myfile.txt copy_of_myfile.txt

16
File Commands - 3

• mv original_file new_filename
• mv original_file new_location
• new_location must already exist
• file keeps same name
• mv original_file new_location/new_filename
• move a file
• examples mv myfile.txt newname.txtmv
  myfile.txt ..mv myfile.txt /usr/bin/students.txt

17
File Commands - 4

• cat file
• cat file1 file2 ...
• display the contents of the file(s) on the screen
• more file
• display the contents of the file on the screen,
  on screenful at a time (press space for the next
  screen, return to advance one line)?
• gedit file
• edit the file in the gnome graphical editor

18
Directory Commands

• mkdir dirname
• mkdir path/dirname
• create the directory
• rmdir dirname
• remove the directory (it must be empty)?

19
Shell filename wildcards 1

• it can be useful to match filenames by pattern
• matches any set of characters (or no
  characters)?
• ? matches one character
• examples
• filematches any filename containing file
• .txtmatches any filename that ends in .txt
• thismatches any filename that starts with this

20
Shell filename 2 wildcards

• More examples

21
Shell filename wildcards 3

• More examples
• cat chapter.txtwill output to the screen all
  files that start in chapter and end in .txt
• ls .txtwill list all files that end in .txt
• mv .txt /export/home/alingelbwill move all
  files ending in .txt to the directory
  /export/home/alingelb

22
More useful (text) file commands 1

• grep pattern filesearch for the pattern in the
  file, and output the line(s) containing the
  pattern
• sort filesort the lines of the file in
  alphabetical order
• head filedisplay the first 10 lines of the file

23
More useful (text) file commands 2

• tail filedisplay the last 10 lines of the file
• wc filecount the number of lines, words, and
  characters in the file
• diff file1 file2display the differences between
  the two files

24
File permissions 1

• Every file has read, write, and execute
  permissions (RWX)?
• These are set by the owner, for the owner, the
  group, and everyone else so there are 9
  permissions total (plus a few special ones to be
  discussed later).

25
File permissions 2

• ls -lwill display file permissions, along with
  the group and owner
• example ls -ltotal 3-rwxr-xr-x 2 alingelb
  staff 512 Nov 2 1038 Desktopdrwxr-xr-x
  3 alingelb staff 512 Oct 16 1115
  Documents-rw------- 1 alingelb staff
  40 Nov 2 1213 foonly.txt

26
File permissions 3

• chmod fileis used to change file permissions
• the first is owner permissions
• the second is group permissions
• the third is everyone else permissions
• the is composed of(add the numbers)
• 4 for read
• 2 for write
• 1 for execute

27
File permissions 4

• chmod example
• chmod 744 file
• sets owner to read/write/execute
• sets group to read
• sets everyone else to read

28
Shell theory

• The shell is a command interpreter
• It interfaces between the user and programs and
  the kernel
• It has its own syntax
• In addition to providing access to programs and
  to the kernel, the shell has some powerful
  features of its own, including
• wildcards
• I/O redirection
• scripting

29
I/O management 1

• Every process has 3 channels of information
• standard input
• standard output
• error output
• These can be controlled by the shell
• command gt file
• sends the standard output of the command to a
  file
• command lt file
• sends the contents of a file to the standard
  input of the command
• command gtgt file
• appends the standard output of the command to the
  end of a file

30
std I/O management

• Examples
• ls gt listing.txt
• echo this is a test gt test.txt
• echo the test continues gtgt test.txt
• echo 6 6 gt math.txt
• bc lt math.txt

31
more I/O management

• More I/O redirection
• There is a special empty file/dev/null
• it discards all output
• command 2gt /dev/null
• discards all error output
• exampletouch testfilechmod 000 testfilecat
  testfile 2gt /dev/null
• command1 command2
• send the output of command1 as the input of
  command 2
• example ls wc

32
I/O management pipe

• Advanced example of pipe
• wanted list of users on system. build it
  incrementally using pipe.
• who gives list of users, but there are
  duplicates (because user appears once for each
  session)also, who gives too much information
• using cut to remove extraneous informationwho
  cut -d\ -f1gives list of users, still with
  duplicates
• who cut -d\ -f1 sortsorts list, putting
  duplicates together
• who cut -d\ -f1 sort uniqremoves
  duplicates this is the desired list

33
Review

• Concepts
• Unix history, multiuser/timesharing, kernel,
  shell, man pages, file permissions
• Flow control
• ctrl-C, ctrl-S, ctrl-Q, ctrl-D
• Commands
• echo, bash, date, who, pwd, ls, cd, touch, rm,
  cp, mv, cat, more, gedit, mkdir, rmdir, grep,
  sort, head, tail, wc, diff, chmod, bc
• File paths wildcards
• , ?
• I/O management
• gt, gtgt, lt, , 2gt