1. Unix Basics
Prepared by
Dima Gomaa

2. What Is an Operating System?
• Interface between Users and the Hardware
• Take care of Storage Management
• Take care of I/O device management

3. History of the UNIX Operating System
1969 AT&T Bell Labs UNICS system -designed by Ken
Thompson & Dennis Ritchie
1970 UNICS finally became UNIX
1973 UNIX rewritten in C, making it portable to different hardware
Mid 1970s University of California at Berkeley (BSD) contributed many
important features like vi, C shell etc.
1982 AT & T came back and started commercial production-
Editions ->Systems
Late 1980s AT & T released SVR4 unification of SV3.2,BSD,SunOs &
XENIX
1991 Linux from Linus Torvalds
1990s POSIX Standard, MIT introduced X-Windows
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4. UNIX Architecture – Kernel & Shell
User Shell Kernel Hardware
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5. More Features of UNIX
• Hierarchical file system
• Multi tasking
• Multi user
• Pattern matching (wildcard characters)
• Programming facility
• Documentation
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6. Command Line Format
Syntax:
$ command [-options] [arguments]
1. Separation
2. Order
3. Multiple options
4. Multiple arguments
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7. Basic Commands(1)
 ls list files and directories
 ls -a list all files and directories
 mkdir make a directory
 cd directory change to named directory
 cd change to home-directory
 cd ~ change to home-directory
 cd .. change to parent directory
 pwd display current dir path
 useradd add new user in the system
 usermod modify user
 userdel delete user
 groupadd add new group in the system

8. Basic Commands(2)
 cp file1 file2 copy file1 and call it file2
 mv file1 file2 move or rename file1 to file2
 rm file remove a file
 rmdir directory remove a directory
 cat file display a file
 more file display a file a page at a time
 who list users currently logged in
 lpr -Pprinter psfile print postscript file to named printer
 * match any number of characters
 ? match one character
 man command read the online manual page for a
command

9. Basic Commands(3)
 command > file redirect standard output to a file
 command >> file append standard output to a file
 command < file redirect standard input from a file
 grep 'keyword' file search a file for keywords
% grep science science.txt
 wc file count number of lines/words/characters in file
% wc -w science.txt
 sort sort data (numerically or alphabetically)
Ex:
to sort the list of object, type
% sort < biglist
and the sorted list will be output to the screen.

10. The File System Hierarchy
/
usr etc home dev var tmp
bin sbin dsk rdsk adm sadm
ls who
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11. File Path name
A sequence of file names, separated by slashes (/), that
describes the path, the system must follow to locate a
file in the file system
Absolute pathname (start from the /-directory):
Eg: /export/home/user1/file1
Relative pathname (start from the current directory)
./test1 (. = current directory)
../team03/.profile (.. = parent directory)
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12. File Characteristics
$ ls -l
-rw-r--r-- 1 user3 class 37 Jul 24 11:06 f1
-rwxr-xr-x 1 user3 class 52 Jul 24 11:08 f2
drwxr-xr-x 2 user3 class 1024 Jul 24 12:03 memo
File Links Group Name
Type Timestamp
Owner Size
Permissions
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13. Who can access a File?
The UNIX system incorporates a three-tier structure to define who
has access to each file and directory:
user The owner of the file
group A group that may have access to the file
other Everyone else
• The ls -l command displays the owner and group who has
access to the file.
$ ls -l
-rw-r--r-- 1 user3 class 37 Jul 24 11:06 f1
-rwxr-xr-x 1 user3 class 37 Jul 24 11:08 f2
drwxr-xr-x 2 user3 class 1024 Jul 24 12:03 memo
| |
owner group
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14. File system security (access rights)
-rwxrwxrwx a file that everyone can read, write and execute
(and delete).
-rw------- a file that only the owner can read and write - no-
one else can read or write and no-one has
execution rights (e.g. your mailbox file).

15. Unix File Permissions
 File type, owner, group, others
drwx------ 2 jjoshi isfac 512 Aug 20 2003 risk management
lrwxrwxrwx 1 jjoshi isfac 15 Apr 7 09:11 risk_m->risk management
-rw-r--r-- 1 jjoshi isfac 1754 Mar 8 18:11 words05.ps
-r-sr-xr-x 1 root bin 9176 Apr 6 2002 /usr/bin/rs
-r-sr-sr-x 1 root sys 2196 Apr 6 2002 /usr/bin/passwd
 File type: regular -, directory d, symlink l, device b/c, socket s, fifo f/p
 Permission: r, w, x, s or S (set.id), t (sticky)

16.  chmod [options] file change access rights for named file
For example, to remove read write and execute permissions on the file
biglist for the group and others, type
% chmod go-rwx biglist
This will leave the other permissions unaffected.
To give read and write permissions on the file biglist to all,
% chmod a+rw biglist

17. Default Permissions
The default protections for newly created files and directories
are:
File -rw-r—r-- 644
Directory drwxr-xr-x 755
These default settings may be modified by changing the umask
value.
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18. umask - Permission Mask
Umask specifies what permission bits will be set on a new
file or directory when created.
New Directory: 777 – 022 755  rwxr-xr-x
New File : 666 – 022 644 rw-r—r—
The default value of umask is set in /etc/profile. This can be
changed for all the users or a particular user
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19. chown - Change File Ownership
Syntax:
chown owner [:group] filename ...
Changes owner of a
file(s) and, optionally, the
Example: group ID
$ id
uid=101 (user1), gid=101 (group1)
$ cp f1 /tmp/user2/f1
$ ls -l /tmp/user2/f1
-rw-r----- 1 user1 group1 3967 Jan 24 13:13 f1
$ chown user2 /tmp/user2/f1
$ ls -l /tmp/user2/f1
-rw-r----- 1 user2 class 3967 Jan 24 13:13 f1
Only the owner of a file (or root) can change the ownership of the file.
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20. The chgrp Command
Syntax:
chgrp newgroup filename ...
Example:
$ id
uid=303 (user3), gid=300 (class)
$ ls -l f3
-rw-r----- 1 user3 class 3967 Jan 24 13:13 f3
$ chgrp class2 f3
$ ls -l f3
-rw-r----- 1 user3 class2 3967 Jan 24 13:13 f3
$ chown user2 f3
$ ls -l f3
-rw-r----- 1 user2 class2 3967 Jan 24 13:13 f3 20

21. su - Switch User Id
Syntax:
su [user_name]
Change your effective user ID and group ID
Example:
$ ls -l f1
-rwxr-x--- 1 user1 group1 3967 Jan 24 23:13 class_setup
$ id
uid=303 (user1), gid=300 (group1)
$ su – user2
Password:
$ id
uid=400 (user2), gid=300 (group1)
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22. Special File Permissions – setuid, setgid,
sticky bit
 setuid – changes the effective user id of the user to the owner of
the program
 chmod u+s f1 or
– chmod 4744 f1
 setgid – changes the effective group id of the user to the group
of the program
 chmod g+s f1 or
 chmod 2744 f1
 sticky bit – ensures the deletion of files by only file owner in a
public writable directory
 chmod +t f1 or
 Chmod 1744 f1
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23. What Is vi?
• A screen-oriented text editor
• Included with most UNIX system distributions
• Command driven
• Categories of commands include
– General administration
– Cursor movement
– Insert text
– Delete text
– Paste text
– Modify text
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24. Starting and Ending a vi
Session
vi [filename] Start a vi edit session of file
Example:
$ vi testfile
- If the file doesn’t exist, it will be created
- Otherwise vi will open the existing file
All modifications are made to the copy of the file brought into
memory.
:wq or :x or <shift-zz> write and quit
:w write
:q quit
:q! Quit without saving
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25. Cursor Control Commands
1G
<ctrl-b>
H
k
<up-arrow>
0 $
b,B w,W
h l
<left-arrow> <right-arrow>
<down-arrow>
j
L
<ctrl-f>
G
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26. Input Mode: i, a, O, o
i will insert character at the present cursor position
I will insert character at the beginning of the line
a will append character at the present cursor position
A will append character at the end of the line
o will insert a blank line below
O will insert a blank line above
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27. Deleting Text: x, dw, dd, dG
x deletes the current character
dw deletes the current word
dd deletes the current line
dG delete all lines to end of file, including current line.
With any of these you can prefix a number
Example: 3dd will delete 3 lines
d$ to delete to the end of the line
d0 to delete to the start of the line
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28. Copying, moving and
changing Text
yy copy the line
yw copy the word p will paste the yanked lines below
dw cut the word P will paste the yanked lines above
dd cut the line
r will overwrite the current character
R will replace all text on the right of the cursor position
cw will replace only the current word
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29. Searching for Text: /, n, N
/director will locate for the first occurrence of the
pattern ‘director’
n to locate the next occurrence
N to locate the previous occurence
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30. Monitoring Process
The ps command dislays process status information
$ ps -f
UID PID PPID ... TTY ... COMMAND
john 202 1 ... tty0 ... -ksh
john 204 202 ... tty0 ... ksh
john 210 204 ... yyu0 ... ls -R /
john 212 204 ... tty0 ... ps -f
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31. Shell Scripting
 Shell scripting skills have many applications, including:
 Ability to automate tasks, such as
 Backups
 Administration tasks
 Periodic operations on a database via cron
 Any repetitive operations on files
 Increase your general knowledge of UNIX
 Use of environment
 Use of UNIX utilities
 Use of features such as pipes and I/O redirection

32. Examples of Shell Scripting
 Store the following in a file named simple.sh and execute it
#!/bin/sh
# Show some useful info at the start of the day
date
echo Good morning $USER
cal
last | head -6
 Shows current date, calendar, and a six of previous logins
 Notice that the commands themselves are not displayed, only
the results