Overview
A summary of Linux permissions.
How to Read Permissions
File Type
The first character represents the file type.
-
- File
- d Directory
- l Symbolic link
The following three-character groups represent permissions for the file owner.
2nd to 4th characters: User - permissions for the file owner
5th to 7th characters: Group - permissions for the file group
8th to 10th characters: Others - permissions for others
Types of Permissions
There are three types of permissions.
- r Read
- w Write
- x Execute
The meaning changes depending on whether it is a file or a directory, so be careful.
For Files
- r Read - can read the contents of the file
- w Write - can edit the contents of the file
- x Execute - can execute the file as a program
For Directories
- r Read - can list the files within the directory
- w Write - can create or delete files within the directory*1
- x Execute - can navigate into the directory*2
*1 Files within the directory can be deleted even without write permission.
*2 If execute permission is not granted to the directory, you cannot navigate into that directory.
Example
ls -l example.md
-rw-r--r-- 1 bmf staff 652 Jul 18 11:45 example.md
Permissions for example.md:
File type: File
User permissions: Read/Write
Group permissions: Read
Other permissions: Read
How to Set Permissions
There are two methods: specifying with numbers and specifying with letters. The chmod command is used to set permissions.
Specifying with Numbers
chmod mode target_filename
Use three digits to specify permissions.
The hundreds place is for the user, the tens place is for the group, and the units place is for others.
- 4 r Read
- 2 w Write
- 1 x Execute
To grant multiple permissions, specify the sum of the numbers.
For example, to grant read and write permissions, specify 6; to grant all permissions, specify 7.
ls -l example.md
-rw-r--r-- 1 bmf staff 652 Jul 18 11:45 example.md
chmod 766 example.md
-rwxrw-rw- 1 bmf staff 1788 Jul 18 11:57 example.md
Specifying with Letters
chmod target+operation+permissions target_file
Specify the target, operation, and permissions using letters and symbols.
Target
- u User
- g Group
- o Others
- a All
Multiple targets can be specified.
For example, if you want to target both user and group, specify ug.
Operation
- = Set to specified permissions
-
- Add specified permissions
-
- Remove specified permissions
Permissions
- r Read
- w Write
- x Execute
Multiple permissions can be specified.
For example, if you want to specify read and write, specify rw.
ls -l example.md
-rw-r--r-- 1 bmf staff 652 Jul 18 11:45 example.md
chmod a+rw example.md
-rw-rw-rw- 1 k.takeuchi staff 2877 Jul 18 12:24 example.md
References
By the Way
ls -l example.md
-rw-r--r-- 1 bmf staff 652 Jul 18 11:45 example.md
The number 1 displayed after the permissions in the output of ls -l indicates the number of hard links.
