basic unix © mcgraw hill 2000. all rights reserved
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Basic UNIX
© McGraw Hill 2000. All rights reserved.
Introduction
UNIX is an operating system UNIX has 3 main parts:
Kernel - manages hardware resources like terminals and printers
File System - accesses files; tree structured Shell - interacts with users
UNIX is interactive UNIX is multi-tasking UNIX is multi-user
System Prompt % or $ or computername> System prompt indicates that system is
waiting for a command Enter commands at the prompt:
%pine %menu %date %who %help %whoami %cal %cal arg (arg = year) %man arg (arg = command name)
Note: UNIX commands are case sensitive!
File System
File is a container for data
3 kinds of files:
Directories (like folders) Container for files and other directories
Sub-directory is a directory contained within another
directory
Ordinary files
Special files
File Structure
Directories and files are organized in a tree-like hierarchy
Directory at the top is known as the root directory and is represented as a /
Some standard subdirectories under the root directory are etc, usr, and tmp
UNIX Tree-like Hierarchy
/
mnt n bin tmp_mnt
m
00 37 39
jrp hdb ehepp
root
Full pathname:
/n/m/37/ehepp
Home Directory
“Home” directory is where you find yourself when you log in
To print the name of the directory you are in: %pwd (print working directory)
Shows the “full pathname” eg. /n/m/37/ehepp
Pathnames
A pathname is the concatenation of the directories you traverse to reach a file
A relative pathname is the concatenation of the directory names from where you are currently “located” in the file hierarchy
A full pathname specifies the complete path traversed starting with the root (also called an absolute pathname)
File and Directory Organization You can create and maintain files and
directories in your home directory Use subdirectories to organize files Use the mkdir command to create a
subdirectory: %mkdir myCS403stuff
New subdirectory will be be created in current directory (also called working directory)
Moving Through the File Structure Using the cd command cd is the change directory command
Specify a directory name as an argument to cd command to move to that directory within the current directory %cd myCS403stuff
Specify a full pathname as an argument to change directories %cd /n/m/37/ehepp/myCS403stuff
cd Command (continued)
%cd or %cd ~ will put you in your home directory: %cd %pwd /n/m/37/ehepp
To move up one one level in a directory hierarchy, follow the cd command with two dots: %cd .. %pwd /n/m/37
File Manipulation
Rename a file (move)
%mv index.html index.old
Delete a file (remove)
%rm -i mystuff.txt
Look at contents of a file
%more index.html
Copy a file %cp -i index.html index.bkup
Create a file %pico myfile.html
Update a file %pico myfile.html
Other UNIX Commands
List a directory’s contents %ls
List a directory’s contents in the “long form” %ls -l
List a directory’s contents including hidden files %ls -a
Remove a directory %rmdir myCS403stuff
File Permissions
Permissions provide a measure of security by establishing who is able to access what files and directories, and how they can be accessed
File and directory permissions can be displayed using the ls -l command%ls -l
-r--r--r-- 1 marymc Spanish 167 Jul 27 08:15 file.txt
Permission Codes
3 identifiers specify who can access the file: User who owns file – u (aka “owner”) Users who are members of the same group as the
file owner - g All other users - o (aka “rest of the world”)
3 levels of access: Read - r Write - w Execute – x (or “search” for directories)
Permission Codes (continued)
r w x r w x r w x
u g
Nine characters are split into three sets of three characters each:
- 1st set identifies permissions for the user- 2nd set identifies permissions for the group- 3rd set identifies permissions for others (the rest of the world)
o
Permission Code Examples
r - - r - - r - -user, group members, and others can read the file
r - - - - - - - -only the user can read the file
r w - r - - - - -user can read and write the file, group members
can read the file, all others are denied access
Changing Permissions Use the chmod command to change
permissions Two ways to use chmod command:
Symbolic form Numeric form
Symbolic Form of chmod Uses permission code symbols (u, g, o, r,
w, x) to add and remove permissions Basic form of command:
To add a permission: %chmod [who]+[access] filename eg. - %chmod o+r README To remove a permission: %chmod [who]-[access] filename eg. - %chmod o-w README
Note: Can set more than one at a timeeg. - %chmod o+r,og-w myfile.html
Numeric Form of chmod
Think of 9 character permission codes as 9 on/off switches represented by 1/0r w x r w x r w x 1 1 1 1 1 1 1 1 1
r w x r - x r - - 1 1 1 1 0 1 1 0 0 View the binary representation as 3 triplets
1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 0 0
7 7 7 7 5 4
Numeric Form of chmod (continued)
Use chmod command with octal value representing desired permissions
Examples:%chmod 777 myfile.html
1 1 1 1 1 1 1 1 1 r w x r w x r w x
%chmod 711 mydirectory1 1 1 0 0 1 0 0 1 r w x - - x - - x
%chmod 644 myfile.html1 1 0 1 0 0 1 0 0 r w - r - - r - -
File Names
UNIX is case sensitive so Myfile.html is not the same as myfile.html
Avoid special characters in file names: < > | & *
Extension at end of file name indicates type of file: .html or .htm - Web page .c - C program file .ps - postscript file
* represents any arbitrary character string eg. - %ls *.html
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