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File and Directory Permissions (chmod, chown)
In Ubuntu (and Linux in general), file and directory permissions are crucial for security and access control. They define who can read, write, or execute a file or directory. The commands chmod
and chown
are used to change these permissions and ownership, respectively.
File and Directory Permissions
Each file and directory has three types of permissions for three categories of users:
- User (u): The owner of the file.
- Group (g): Other users who are in the same group as the owner.
- Others (o): All other users.
The permissions are represented as:
- r: Read (4)
- w: Write (2)
- x: Execute (1)
Permissions can be represented either symbolically (e.g., rwx
) or numerically (e.g., 7
).
Example 1: Viewing Permissions
ls -l
Output:
-rwxr-xr-- 1 user group 4096 Aug 10 10:00 myfile.txt
-rwxr-xr--
shows the permissions:rwx
(user): The owner can read, write, and execute.r-x
(group): Group members can read and execute.r--
(others): Others can only read.
chmod
Command: Changing Permissions
You can change permissions using the chmod
command.
Example 2: Changing Permissions Symbolically
chmod u+x myfile.txt
- Adds execute (
x
) permission for the user (owner).
Example 3: Changing Permissions Numerically
chmod 755 myfile.txt
- Sets permissions to:
7
(rwx) for the user5
(r-x) for the group5
(r-x) for others
chown
Command: Changing Ownership
The chown
command changes the owner and group of a file or directory.
Example 4: Changing the Owner
sudo chown newuser myfile.txt
- Changes the owner of
myfile.txt
tonewuser
.
Example 5: Changing Owner and Group
sudo chown newuser:newgroup myfile.txt
- Changes the owner to
newuser
and the group tonewgroup
.
Example 6: Changing Ownership Recursively
sudo chown -R newuser:newgroup /mydirectory
- Changes the owner and group for all files and subdirectories within
/mydirectory
.
Summary
- Permissions determine what actions can be performed on a file/directory (read, write, execute).
chmod
modifies these permissions.chown
changes the owner and group.
These tools are essential for managing access to files and directories in Ubuntu.
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