Permission Groups
There are below three permission groups for each file and directory
- Owner : The Owner permissions apply only the owner of the file or directory.
- Group : This permissions apply only to the group that has been assigned to the file or directory.
- Others : This permissions apply to all other users on the system.
If the group of the file is the same as the user’s group, the group permission determine the access. Also if the user is not the file owner, and is not in the group, then the other permission is used.
Permission Types
Each file or directory has three permission types:
- Read (r) : Allow a user to read the contents of the file or list the files within the directory.
- Write (w) : It refer to a user’s capability to write or modify a file. In case of directory, it allows the user to create, rename, or delete files and modify the directory’s attributes.
- Execute (x) : It refers to a user’s capability to execute a file or view the contents of a directory and access directories inside.
You can view the permissions of file and directory by reviewing the output of the ls -l command in the terminal. The permission in the command line is displayed as:
- The first character is the special permission flag that can vary.
- Following set of three characters (rw-) is for the owner permissions.
- Second set of three characters (r–) is for the Group permissions.
- Last set of three characters (r–) is for the other Users permissions.
Following that grouping number displays the number of hard links to the file. The last piece is the Owner and Group assignment to which this file belongs.
Modifying the Permissions
Permissions of file and directory are edited by using the command chmod. Notation use for permission group are:
- u : Owner
- g : Group
- o : Others
- a : All users
Notation used to represent permission types are:
- r : Read
- w : Write
- x : Execute
Assignment Operator + (plus) is used to add permission and – (minus) to remove the specific permissions. For an example, file named hello.txt currently has the permissions set to rw-r–r–. Now to add the execute permission for the user, execute below command
chmod u+x hello.txt
Permissions can also be modified using binary notation. The first number represents the Owner permission; the second represents the Group permissions; and the last number represents the permissions for all other users.
chmod 640 hello.txt
Each number is a binary representation of the rwx string:
- r : 4
- w : 2
- x : 1
So to allow owner to have read, write and execute permissions ie rwx------, you would enter chmod 700.
Recursive Permissions
You can give permission to folder and all its contents using option -R i.e recursive permissions. Below command will give permissions to all files currently in the folder and files added in the future without giving permissions to the directory itself.
chmod -R 777 ./
To apply permissions to all the folder and new folders added in the future without giving permissions to the files itself, execute below command
chmod -R 777 /www/store
Copy File Permissions
chmod command also allows to copy permissions of one file to another. Use –reference option to copy permissions from one file to another. For example the below command will set permissions on file2 same as that of file1.
chmod --reference=file1 file2
Permissions of the file2 file were cloned and set to be the same as permissions of file1 file.