User Groups and Permissions

– Users

Types: UID

1.         Root user       0

2.         System users            1-499

3.         normal users >500

/etc/passwd – User database



X=Encricpted password



Types:                        GID

1. Root users group 0

2. System User group          1-499

3. Normal user group          >500

/etc/group database file



X=encripted password


User Information commands

# whoami (displays login name)




above three commands displays list of currently logged in users



above two commands displays the list of groups of which the logged in user is

a member

Unit 5 Uses, Groups & Permission (contd…)

* Switching users account

# su – username

eg. # su – sbogati (It asks password for loging user)

* User Categories

Owner -u

Group -g



Permission types:

Permissions  Symbolic represatation       Numeric value(octual value)

Read                          r                       4

Write                           w                     2

Execute                                 x                      1

No Permission                      –                       0

Permission operators

Options                                  Meaning

——-                           ———

+                                  to add permission

[on existing one]

–                                   to remove pewrmission

(from existing one)

=                                  to absolutly assign permission

(overwriting existing one)

* Effects of permission:

Permission    Effects on a file                    Efects on a dir

1. Read (r)     1. It allows to view the         1. It allows to list the content                                                                         s of a dir


2. Write (w)    2. It allows to modify the     2. It allows to create/remove/re                                                                     name files/dirs. inside the


[cat>, mkdir, mv, rm etc.]

3. Execute (x)            3. It allows to execute the file

if it is a program file.         3. It allows to enter into the



contents of a file

[vi nano,..]

contents of a file

[cat, vi, less

* Umask


It is a value that determines default permission (ig. permission at the time of

file/dir. creation) on a file or dir.


1. – type

2. d dir

3. l symbolic link

4. b block device file

5. c character device file

Above 9 tpye are called permission string

first 3 are owners permission, sedond 3 are group permission and last 3 are others permissions