Understanding Linux Permissions
Linux file permissions control who can read, write, or execute a file or directory. They are managed for three distinct categories of users:
User (U) - The Owner
- This refers to the individual user who owns the file or directory.
- When you create a new file or directory, you are typically its owner by default.
- The 'User' permissions apply only to this specific owner.
Group (G) - Group Members
- This refers to a group of users defined on the system.
- Users can be members of one or more groups.
- The 'Group' permissions apply to all users who are members of the file's assigned group. This is useful for team projects where multiple users need similar access.
Others (O) - Everyone Else
- This refers to all other users on the system who are not the owner and are not members of the file's assigned group.
- These permissions are often the most restrictive to prevent unauthorized access by general users.
Each of these categories (User, Group, Others) can have Read, Write, and Execute permissions:
Read (r / 4)
- For Files: Allows viewing the contents of the file. You can open and read it.
- For Directories: Allows listing the contents of the directory (i.e., seeing what files and subdirectories are inside).
Write (w / 2)
- For Files: Allows modifying, saving changes to, or deleting the file.
- For Directories: Allows creating new files or subdirectories within that directory, deleting existing files or subdirectories, and renaming files within that directory.
Execute (x / 1)
- For Files: Allows running the file as a program or script. Without execute permission, you can't run a script even if you can read its contents.
- For Directories: Allows "entering" or traversing into the directory. Without execute permission, you cannot `cd` into the directory or access files within it, even if you have read permission to list its contents.
The numbers (4, 2, 1) represent the octal values for each permission, which are summed up to form the 3-digit octal permission mode (e.g., rwx = 4+2+1 = 7).