1 © 2001 John Urrutia. All rights reserved. Chapter 4 The LINUX Filesystem

1© 2001 John Urrutia. All rights reserved.

Chapter 4

The LINUX FilesystemThe LINUX Filesystem


TopicsThe Hierarchical File System

Directory and Ordinary Files

Working With Directories

Access Permissions

Links


Hierarchical File SystemsStructured like an upside-down

tree

Grandparents at the top

Parents follow

Then Children

Topics


Child 1 Child 2 Child 3

Grandparent

Parent aunt uncle

/Alice /Bobby /Carol

/home /tmp /bin

Hierarchical Structure/

(aka root)


Hierarchical File SystemsDirectories and ordinary files

Directories / sub-directoriesSpecial files used for grouping

Ordinary FilesContain the kitchen sink


Directory assistanceDirectories provide an organized

method to access ordinary files.path –

A series of directory files traveling from the root to the ordinary file.

pathname – The sequenced listing of directory names

from the root to the ordinary file.


FilenamesFilenames

Max length 255 characters

A thru Z, a thru z, 0 thru 9 _ . ,Some file systems limit these to 14 characters

Make them meaningful30952344 IMd12CRU OOicu812


Filename ExtensionsBegins with a period

Generally are optional

Used by applications to identify specific file needed by the applicationExamples: CPP TXT INI


Invisible FilesMust start with a period

Normally not displayed

Used by Unix for special purposes

Use “ls –a” to see these

˜


TopicsThe Hierarchical File System

Directory and Ordinary Files

Working With Directories

Access Permissions

Links


Creating a directorymkdir – utility creates a directory

The argument can either specify an absolute pathname or a relative pathname

mkdir mydirectoryIn this example “mydirectory” will be

created under the current or working directory


Directory fileTwo invisible files are created for

each directory createdOne is the pathname of the working

directory named “”

Two is the pathname of the parent directory named “ ”cat ./Test.filecat Test.file


Path (to glory or destruction)

Every file has a PATHNAMEAbsolute Pathnames begin with the root

(/)

Each directory in the hierarchy from the root to the file is separated by a slash


Test.file

Path example:

/Alice /Bobby /Carol

/home /tmp /bin

//

/home

/Bobby

Test.file

/home/Bobby/Test.file


Absolute & Relative PathAbsolute path is fully qualified

cat /home/Bobby/Test.file

Relative path is based on the working directorypwd – Print Working Directory

/home/Bobbycat Test.file


The Working DirectoryYou’re working directory is assigned

by the login process.

To access files in working directory simply refer to the filename no path is needed.

Files outside your working directory require a pathname.


Your Working DirectoryGenerally you’re working directory

will be/home/userid


Important Directories and FilesThe root - / (of all evil)

/root – Home directory for root

/boot – static files of the boot loader

/bin – files needed to boot the system

/sbin – /usr/sbin system admin. utilities

/dev – device files

/etc – admin. and configuration files


Important Directories and Files/tmp – temporary files

/home – user home directories

/lib – shared libraries

/mnt – mount point of temporary partitions

/tmp – temporary files

/usr – 2nd major hierarchy – rarely change

/proc – kernel and process information


Changing working directorypwd – displays your working directory

cd - change directoryBy default places you in your working

directory(ie /home/userid)

cd ~ (will do the same thing)

cd path/path1 – changes relative to your working directory


Access PermissionsEvery file has access “permissions”

associated with them.r – read

w – write

x – execute


Access PermissionsEvery ordinary file has three access

groups.Owner or User

User who created the file

GroupUsers who are associated

OthersThe rest of the world


Access PermissionsDirectory file access “permissions”

r – read the directory

w – write the directory

x – search the directory


Access PermissionsSetting default “permissions”

umask 000One digit each for U,G,OOctal value representing the 3 bits

R W X R W X R W X

4 2 1 4 2 1 4 2 1


Directory Utilitieschmod – change access mode

u – User or owner

g – group

o – others

+ – add permission

- – remove permission


Directory Utilitiesmkdir – Make Directory

mkdir –p directory-listThe –p option creates the parent

directory if it doesn’t existdirectory-list

One or more directories separated by space


Directory Utilitiesrmdir – remove Directory

rmdir directory-listdirectory-list



Directory Utilitiesrm – remove

rm –r directory-listThe –r option removes recursively. All

subdirectories are removeddirectory-list



Directory Utilitiescd – change directory

cd directory The directory (pathname) becomes the

working directory


Linksaka – Also Known As

Creates an entry in the directory that point to an existing file or directory.

Doesn’t create a copy of the file


Links – Hard and SymbolicHard links

Behave just like a file

Cannot distinguish the original filename from the link

Cannot cross file systems

Directory links by superuser only


Links – Hard and SymbolicSymbolic links

Indirect pointer to file or directory

Can be created by anyone

Can reside anywhere

Can become an orphan


Link Utilityln – Make a link entry

ln [–s] filename linkname

ln [–s] file-list directory

Documents

1 © 2001 John Urrutia. All rights reserved. Chapter 4 The LINUX Filesystem