Permissions in Linux

Create three users:

Example:

[root@test119 ~]# useradd kavita
[root@test119 ~]# useradd ramu
[root@test119 ~]# useradd srinu

Make ramu the member of the group kavita

Example:
[root@test119 ~]# gpasswd -a ramu kavita
Adding user ramu to group kavita


Create a directory


Example:

[root@test119 ~]# mkdir /linux

Check the default permission of the above created directory

[root@test119 ~]# ls -ld /linux/
drwxr-xr-x 2 root root 4096 Aug 28 11:26 /linux/

Give full permissions to the above created directory

Example using absolute mode

[root@test119 ~]# chmod 777 /linux/
                         (or)
Example using symbolic mode

[root@test119 ~]# chmod ugo=rwx /linux/

Check the permissions on the directory


[root@test119 ~]# ls -ld /linux/
drwxrwxrwx 2 root root 4096 Aug 28 11:26 /linux/

Log in as the user kavita

Example:

[root@localhost~]# su -kavita

As user kavita create a file inside the above created directory

-sh-4.1$ cd /linux/
-sh-4.1$ ls
-sh-4.1$
-sh-4.1$ cat >fedora
This is a version of linux operating system
ctrl+D

Check the permisson on the file


Example: 

-sh-4.1$ ls -l
total 4
-rw-r--r-- 1 kavita kavita 44 Aug 28 11:41 fedora

Explaination

1. The user kavita has Read and Write permission on this file
2. The group kavitha has read and write permisson on this file (as ramu is a member of the group kavita he     will also have rad and write permisson).
3. Others will have read only permisson ( as srinu belong to others he will have only read permisson).


To check the permissons


Example:- As kavita try to read and add some content to the file

-sh-4.1$ cat fedora
This is a version of linux operating system
-sh-4.1$ cat >> fedora
This line has been added by kavita
-sh-4.1$ cat fedora
This is a version of linux operating system
This line has been added by kavita

Example:- As ramu try to read and add some content to the file ( open another terminal and do the following)

-sh-4.1$ su - ramu
Password:
-sh-4.1$ cd /linux/
-sh-4.1$ ls
fedora
-sh-4.1$ cat fedora
This is a version of linux operating system
This line has been added by kavita
-sh-4.1$ cat >> fedora
This line has been added by ramu

Example:- As srinu to read and add some content to the file (Open another terminal and do the following)

[root@test119 ~]# su - srinu
-sh-4.1$ cd /linux/
-sh-4.1$ ls
fedora
-sh-4.1$ cat fedora
cat: fedora: Permission denied

Change the permisson on the above file


Example:- Remove write permission for the group kavita

-sh-4.1$ cd /linux/
-sh-4.1$ ls
fedora
-sh-4.1$ chmod g=r fedora
-sh-4.1$ ls -l
total 4
--w-r---w- 1 kavita kavita 106 Aug 28 12:04 fedora


Check the permisson on the above file


Example:- As ramu try to read and add some content to the file

-sh-4.1$ su - ramu
Password:
-sh-4.1$ whoami
ramu
-sh-4.1$
-sh-4.1$ cd /linux/
-sh-4.1$ ls
fedora
-sh-4.1$ cat fedora
This is a version of linux operating system
This line has been added by kavita
This line is added by ramu
-sh-4.1$ cat >> fedora
-sh: fedora: Permission denied

Change the permisson on the above file


Example:- Give write permission for others

-sh-4.1$ su - kavita
Password:
-sh-4.1$ cd /linux/
-sh-4.1$ ls
fedora
-sh-4.1$ chmod 646 fedora
-sh-4.1$ ls -l
total 4
-rw-r--rw- 1 kavita kavita 106 Aug 28 12:04 fedora

check the permisson on the above file

Example:- As srinu try to read and add some content to the file

[root@test119 ~]# su - srinu
-sh-4.1$ cd /linux/
-sh-4.1$ ls
fedora
-sh-4.1$ cat fedora
This is a version of linux operating system
This line has been added by kavita
This line is added by ramu
-sh-4.1$ cat >> fedora
This line has been added by srinu
-sh-4.1$ cat fedora
This is a version of linux operating system
This line has been added by kavita
This line is added by ramu
This line has been added by srinu