2) Permissions

PERMISSIONS

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    v  Some important points

      Ø  / (forward slash) → root (administrator).

      Ø  In terminal: “#” → login with root user.

                      “$” → login with local user.

  v Types of User

      Ø  u → owner

      Ø  g → group

      Ø  o → other user

      Ø  a → all user (owner + group + other user)

  v Types of Permission

In Linux, there are three types of permission for file and directory.

      Ø  r → read

      Ø  w → write

      Ø  x → execute

  v File or directory permissions

  v File types

- → Regular file

             d → Directory

              l → Symbolic link or soft link

  v Umask value

 Linux Operating System has different umask value for root user and local user.

      Ø  Umask value for root user → 022

      Ø  Umask value for local user → 002

  v Base value

In Linux, there are different base value for file and directory.

      Ø  Base value for file → 666

      Ø  Base value for directory → 777

  v Default permission

Linux Operating System has different-different default permission for file and directory in root user and local user.

      Ø  In root account:  Base value – umask value

·         For a file → (666 – 022) = 644 (rw-  r--  r--)

·         For a directory → (777 – 022) = 755 (rwx  r-x  r-x)

      Ø  In local user: Base value – umask value

·         For a file → (666 – 002) = 664 (rw-  rw-  r--)

·         For a directory → (777 – 002) = 775 (rwx  rwx  r-x)

  v Permission value

File and directory permission list given bellow:-

Permission value	Permission order	Permission
0	-  - -	No permission
1	- - x	Only execute
2	- w -	Only write
3	- w x	Write & execute
4	r - -	Only read
5	r – x	Read & execute
6	r w -	Read & write
7	r w x	Read, write & execute

Command → chmod ɸ 764 ɸ directory name

              here, 7 → owner user

                        6 → group user

                        4 → other user

Note: When a file has a normal permission, then any user can delete it.

            System account Id → 01 – 999

            Root account Id → 1000

            Other user Id → 1001 - ……

  v Permission operation

      Ø + →  add the permission                 

      Ø - →   remove the permission

      Ø = → same permission

#        chmod ɸ user name + permission type ɸ file name/directory name ↵

#        chmod ɸ user name – permission type ɸ file name/directory name ↵

  v Some special permission

Ø Uid bit no. → 4

Use → use for make owner permission.

#        Chmod ɸ 4 777 ɸ file name ↵

Ø gid bit no. → 2

Use → use for make group owner permission.

#        Chmod ɸ 2 777 ɸ file name ↵

Ø Sticky bit no. → 1

Use → use for block other permission.

#        Chmod ɸ 1 777 ɸ file name ↵