Overview
There are three components that are in the picture when it comes to managing the permissions of a file.
Permission Groups
- User – Abbreviated by ‘u’
- Group – Abbreviated by ‘g’
- Other– Abbreviated by ‘o’
- All – Abbreaviated by ‘a’
Permission Types
- Read Permission – Abbreviated by ‘r’
- Write Permission – Abbreviated by ‘w’
- Execute Permission – Abbreviated by ‘x’
Operations Definitions
- + is used to add a permission
- – is used to remove a permission
- = is used to set a permission
So o-w means taking away write permission from the other user
Before we see an example let’s see how file permissions are represented when you run ls command
Below are some points about the above diagram
- The first character represents the file type. ‘-‘ means regular file and ‘d’ means directory
- The second to fourth character represents the Read, Write and Execute Permission for the owner.
- The fourth to seventh character represents the Read, Write and Execute Permissions for the group
- The eighth to the tenth character represents the Read, Write and Execute Permissions for the other user
Example
- Create a file temp.txt. Check its permissions.
ls -all | grep temp.txt
-rw-r--r-- 1 root root 0 Aug 9 14:50 temp.txtNotice that the other user only has permission to only read
- Now run command to give write permission to the other user
chmod o+w temp.txt
ls -all | grep temp.txt
-rw-r–rw- 1 root root 0 Aug 9 14:50 temp.txt
See output above. Execute permission is also given to the other user.
- Now run command to take away write permission to the other user
chmod o-w temp.txt
ls -all | grep temp.txt
-rw-r–r– 1 root root 0 Aug 9 14:50 temp.txt
Notice how write permission is taken away from the other user
Note: Check out our system design tutorial series System Design Questions