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CHOWN-CHMOD.md

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CHOWN and CHMOD

1. Changing Ownership with chown

The chown command is used to change the owner and/or group of a file or directory.

Check the Current Owner and Group

To see the ownership of a file:

ls -l filename

Example output:

-rw-r--r-- 1 user1 group1 1234 Feb 14 10:00 file.txt
  • First user1 → File owner
  • Second group1 → File group

Change the Owner of a File

To assign a new owner to a file:

chown newuser filename

Change the Group of a File

To change only the group:

chown :newgroup filename

Change Both Owner and Group

To change both owner and group:

chown newuser:newgroup filename

Change Ownership Recursively

To apply changes to all files inside a directory:

chown -R newuser:newgroup directory/

2. Changing Permissions with chmod

The chmod command modifies read (r), write (w), and execute (x) permissions for the user (u), group (g), and others (o).

Permission Structure

Symbol User Permission Type Numeric Value
r Read Can read the file 4
w Write Can modify the file 2
x Execute Can execute the file 1

To check permissions:

ls -l filename

Example output:

-rwxr-xr-- 1 user group 1234 Feb 14 10:00 script.sh
  • rwx → Owner can read, write, execute
  • r-x → Group can read and execute
  • r-- → Others can only read

Change Permissions Using Numeric (Octal) Mode

chmod 755 script.sh
  • Owner (7) → rwx (4+2+1)
  • Group (5) → r-x (4+0+1)
  • Others (5) → r-x (4+0+1)

Change Permissions Using Symbolic Mode

chmod u+rwx,g+rx,o+r script.sh
  • u+rwx → User gets read, write, execute
  • g+rx → Group gets read and execute
  • o+r → Others get read-only

Common Permission Settings

Command Meaning
chmod 777 file Everyone can read, write, and execute (⚠️ Security risk)
chmod 755 file Owner can read, write, execute; others can read and execute
chmod 644 file Owner can read/write, others can only read
chmod 600 file Only owner can read/write
chmod 400 file Only owner can read (no write/execute)
chmod 000 file No one can access the file

Change Permissions Recursively

chmod -R 755 directory/
  • Applies permissions to all files and subdirectories inside directory/.

Conclusion

  • Use chown to change file ownership.
  • Use chmod to modify file permissions.
  • Use octal (755) or symbolic (u+x) notation for permission changes.
  • Be careful with chmod 777—it gives everyone full control!
  • Use -R for recursive changes.