Lesson Unix file system

Unix File System

Unix File System

File System

Unix Overview

1


File System
The file system has the following qualities:
• Made for power and flexibility
• Navigation is cryptic
• Single root directory
– The root directory is designated /
• Everything in Unix is a file

File System

Directories are special files:
• Hold names of files or directories
• Looks like a hierarchical tree
• Similar to DOS
• Unix uses forward slashes (/)
• DOS uses backslashes (\)

Unix Overview

2

Unix File System

File Attributes

File Attributes
File Name:
• String of characters
• No relevance to periods or other
characters
• Some programs can expect specific
type of file names
– Compilers can expect file extensions

Unix Overview

3


File Attributes
File Path:
• Full path specifies all directories
-> /usr/aci/class02/temp
• Filename used when in current
directory

File Attributes

/

“/” represents the root directory

aci

class02

tempfile

/aci/class02/tempfile

Unix Overview

4


File Attributes
File Permissions:
• Each file has permissions for owner,
group, and others access
• Read, write, and execute are the
permissions
• Permissions can be set different for
owner, group, and others usage
• Permissions apply to directories as well
as files

Unix File System

File Types

Unix Overview

5


File Types
Unix has four file types:

• Ordinary files
• Directory
• Device
• Link

File Types
Ordinary files:
• Text files - ASCI
-> program source code
• Binary files
-> Compiled objects
• Hidden files – profiles or configuration
files
-> Begin with a period
-> Are not displayed when listing files
unless the “all” option is used

Unix Overview

6

File Types

Directory files:
• A directory is considered to be a file
since it also contains information
about its contents, such as file names,
file sizes, and last modification time

File Types

Device files:
• Physical devices are represented as
files the same read() and write()
functions that work on files also work
on devices

Unix Overview

7


File Types
Link files:
• A link file is an alias to an existing file
• Both names use the same physical file
• If the link is removed, the file still
exists
• If the file name is removed with a link
to it, the file remains but uses the link

name

File Types
Example of file types

Unix Overview

8


Unix File System

Working With Directories

Working With Directories

Know where you are to work effectively!
• To change directories
• To manipulate files
• To run processes
Know the directory you are in!!!

Unix Overview

9


Working With Directories

Unix has a command to identify the

current working directory.

• Print Working Directory
– pwd

Working With Directories
pwd Command

Unix Overview

10


Working With Directories

Two other useful commands to know:
• clear
-> clears the screen
• history
-> Displays a list of previous commands

Working With Directories
history Command

Unix Overview

11


Working With Directories

Before clear Command exectues

Working With Directories
After clear Command exectues

Unix Overview

12


Working With Directories
Common Directory Commands:
• Make a directory
-> mkdir <directory name>
• Remove a directory
-> rmdir <directory name>
• Change directories
-> cd <options>

Working With Directories

• When making or removing directories,
remember that Unix is case sensitive.

• However the directory name is typed
will be the only way to reference the
directory name correctly!

Unix Overview

13


Working With Directories
The following commands,
mkdir sourceCode
rmdir SourceCode
are accessing different directories since
the spelling contains different upper
and lower case letters

Working With Directories

•

Unix Overview

When using the mkdir command, the
file created will have the owner’s
permissions

14


Working With Directories

•

When using the rmdir command, the
write permissions must be set

accordingly to allow the removal of
the file and the directory must be
empty:
– rmdir emptyDirectoryName

Working With Directories

•

To remove a directory that is not
empty use the rm command with the
-r command:
– rm –r directoryName

Unix Overview

15


Working With Directories
The change directory command has a
number of variations:

• cd
• cd /directory name/directory name/…
• cd ..
• cd ./directory name/directory name/…

Working With Directories

• Every Unix user should be assigned a
home directory where the user is
place upon completion of logon

• The cd command by itself will return
the user to their home directory

Unix Overview

16


Working With Directories
cd

Working With Directories

• To change from one directory to another
directory, the change directory
command can be used with a complete
directory path starting at the root
directory ( / )

Unix Overview

17


Working With Directories
cd /directory name/ …

Working With Directories

• To return to the previous directory use
the change directory command and
two periods

• Separate change directory command
and the two periods with a space

Unix Overview

18


Working With Directories
cd ..

Working With Directories

• To change from one directory to another
that is more than one directory from the
current directory, use the change
directory command with the current
directory option ( ./)
cd ./next directory/next directory/…

Unix Overview

19

Working With Directories
To display the contents of a directory
use the list command. Depending on
what information you wish to display will
determine what options to include
• List contents of a directory command
– ls <options>
• Options are included by using a space
and a hyphen followed by the list of
options

Working With Directories
The list command has a number of options:
• No options returns a file list
• -a -> include all files (hidden files too)
• -l -> see file information
• -r -> list in reverse order
• -t -> sort by modification

Unix Overview

20


Working With Directories
When using ls –l option, the file information is
read from right to left and includes:
• The file name

• The last modification date and time
• The file size in bytes
• The group of the file owner
• The owner of the file
• The number of links to the file
• The file permissions

Working With Directories
Examples of the ls command

Unix Overview

21


Working With Directories
Examples of the ls command

Unix File System

File Permissions

Unix Overview

22


File Permissions

• Unix has several users and groups

• A user can belong to multiple groups, but
•
•

can be active in only a single group at a
time
Users are assigned a primary group and
can assume the privileges of secondary
groups
Files have user, group, and others
permissions

File Permissions
File permissions are defined for
three levels of access:
• u -> owner/user
• g -> group
• o -> others
When changing permissions by
groups to the same setting, you
can use the all group level:
• a -> all

Unix Overview

23


File Permissions
File permissions define what actions

may be taken on a file in Unix:
• r -> Read
• w -> Write
• x -> Execute

File Permissions

• Read permissions control whether
•
•

Unix Overview

someone can view a file
Write permissions allows or disallows
changes to be made to a file such as
update or delete
Execute permissions control whether
a file can be run

24


File Permissions
The permissions on a file are displayed when
a long list command (ls -l) is performed.
The right-most 10 characters displayed:
• Positon 1 is the file type
• Postions 2-4 are the owner permissions
• Postions 5-7 are the group permissions

• Postions 8-10 are the others permissions

File Permissions
051o:/db01/pmdev/r051o>ls
total 240
drwxrwxr-x
3 pmdev
drwxrwxr-x
3 pmdev
drwxrwxr-x
3 pmdev
drwxrwxr-x
3 pmdev
drwxrwxr-x
4 pmdev
drwxrwxr-x
3 pmdev
drwxrwxr-x
2 pmdev
drwxrwxr-x
2 pmdev
drwxr-xr-x
2 pmdev
drwxr-xr-x 10 pmdev
-rw-r--r-1 pmdev

•
•
•
•

Unix Overview

File Type
User Permissions
Group Permissions
World Permissions

-lrt
pmdev
pmdev
pmdev
pmdev
pmdev
pmdev
pmdev
pmdev
pmdev
pmdev
pmdev

96
96
96
96
96
96
16384
8192
8192

8192
45

Column
Columns
Columns
Columns

May
May
May
May
May
May
May
May
May
Jun
Jun

4
4
4
4
4
4
9
13
19
22

27

2005
2005
2005
2005
2005
2005
2005
2005
2005
2005
2005

fh
hm
ip
mc
sz
vs
dcllib
testdata
script
PMJournalFeed
afiedt.buf

1
2-4
5-7
8-10

25