1. January 26th, 2004 Class Meeting 2
Unix Filesystem
January 26th, 2004
Class Meeting 2
* Notes adapted by Christian Allgood from previous work by other members of the CS faculty at Virginia Tech

2. Unix Filesystem The filesystem is your interface to:
physical storage (disks) on your machine
storage on other machines
output devices
Everything in Unix is a file (programs, textfiles, peripheral devices, terminals)
There are no drive letters in Unix – the filesystem is a logical view of the storage devices

3. Working Directory
Working Directory – the current directory in which you are located
pwd (print working directory) command outputs the absolute path (more later) of your working directory
Unless you specify another directory, commands will assume that you want to operate on the working directory

4. Home Directory Directory for users to store personal files
At login, your working directory will be set to your home directory
The path (more later) to your home directory can be referred to by the ~ (tilde) symbol
The home directory of “user1” is represented by ~user1

5. Unix File Hierarchy / bin home etc user1 user2 textfile cs2204 lab1txt
Root Directory: /
Directories may contain plain files or other directories
Result is a tree structure for the filesystem
Unix does not recognize any special filename extensions /
bin
home
etc
user1
user2
textfile
cs2204
lab1txt
lab2txt

6. Unix Paths Separate directories by / Absolute Path Example: / bin home
start at root and follow the tree
Example:
/home/user1/textfile
~users1/textfile
~/textfile /
bin
home
etc
user1
user2
textfile
cs2204
lab1txt
lab2txt

7. Unix Paths (cont) Relative Path / bin home etc user1 user2 textfile
start at working directory
. . – level above
. – working directory /
bin
home
etc
user1
user2
textfile
cs2204
lab1txt
lab2txt

8. Some Standard Directories
/ - root directory
/bin – standard commands and utilities
/dev – block and character device directory
/etc – host-specific configuration files and directories
/home – users directory
/lib – library directory
/sbin – system commands and utilities (needed to boot)
/tmp – temporary files
/usr – most user utilities and applications
/var – files that vary as the system runs (logs, spools)

9. Changing Directories cd – changes the working directory
cd <directory_path>
can use absolute or relative path names
cd without any arguments is the same as: cd ~
Examples:
cd /home/user1
cd ../../user1

10. Output of ls -lF We’ll keep coming back to this slide
lrwxrwxrwx 1 callgood Grads 20 Jan 24 20:16 home -> /home/grads/callgood/
-rw-r--r-- 1 callgood Grads Sep 22 10:07 atoll.jpg
drwxr--r-- 2 callgood Grads 64 Jan 24 18:33 cs2204/
We’ll keep coming back to this slide
permissions
user
group
modified date
filename
file type
size

11. Types of Files Plain ( - ) Directory ( d ) Link ( l ) Special
Most files, binary or text
Directory ( d )
Directory is actually a file
Points to another set of files
Link ( l )
Pointer to another file or directory
Special
b – block device (disks, CD-ROM)
c – character device (keyboard, joystick)

12. Manipulating Files touch <file> mv <file1> <file2>
create a new file or change last modified date
mv <file1> <file2>
rename file1 as file2
mv <file1> <dir>
move file1 into the dir directory
mv <file1> <dir/file2>
move file1 into dir and rename as file2
cp <file1> [<file2>|<dir>|<dir/file2>]
copy file with new name, into directory, or both
rm [-i] <file(s)>
remove file or list of files

13. Creating and Removing Directories
mkdir <directory_name>
create a subdirectory of the current directory
rmdir <directory_name>
remove directory
only works for empty directories
rm -r <directory_name>
remove directory and all of its contents, including subdirectories

14. Creating Links ln -s <existing_file> <link_name>
creates a symbolic link
link_name will be a pointer to existing_file which may be in another directory or even on another physical machine

15. File Ownership Each file has a single owner
chown command can be used to change the owner; usually only root user can use this command
Users can also belong to various groups
Groups may have different permissions than everyone else

16. File Permissions
Permissions are used to allow or disallow access to files or directories
Three types of permission:
Read ( r )
Write ( w )
Execute ( x )
Permission exists on three levels:
User ( u )
Group ( g )
World ( o )

17. File Permissions (cont)
chmod <mode> <file(s)>
chmod 700 textfile
chmod g+rw textfile
r w x user
r w x group
r w x world
ugo
+/-
rwx

18. File Modification Date
Last time a file was changed
Useful when . . .
there are many copies of a file
many users are working on a file
touch command can be used to update the modification date to the current date (or to create a file if it doesn’t exist)

19. Looking at File Contents
cat <filename(s)>
short for concatenate
output the contents of the file all at once
more <filename(s)>
output the contents of the file one screen at a time
allows forward and backward search

20. Getting Help on Unix Commands
man <command_name>
shows all of the documentation for a command (more-style output)
apropos <keyword>
shows you all of the commands with the specified keyword in their description