In linux there the file access is based under three categories
CurrentUser - Users in Group - Other Users
drwxr-xr-x
drwxr – CurrentUser can read, write and execute
xr – Users in Group can read and execute
x – Users can execute
>>ls -l -rw-r--r-- 1 root root 0 Apr 14 17:19 test.txt
The test.txt file has only Read and Write access (rw) for Current User – Read access for Users in Group – Read access for other Users
>>chmod u+x test.txt
Now the test.txt file has Execute access along with Read and Write as below
>>ls -l -rwxr--r-- 1 root root 0 Apr 14 17:19 test.txt
Giving Read wrtite to Group
>>chmod g+r test.txt
Giving read right to Current User, Group Users and Other Users
>>chmod a+r test.txt
Giving Execute right to Other Users
>>chmod o+x test.txt
rwx – 111 7
r-x – 101 5
rw- – 110 6
rw- – 101 4
-wx – 011 3
-w- – 010 2
–x – 001 1
— – 000 0
Example of binary format
>>chmod 752 test.txt
Current User can rwx
Group User can r-x
Other User can -w-
Giving Multiple Permission for Multiple User Types at Once
>>chmod u+r, o+x test.txt