Manage File Permissions and Ownership

In this lesson, we’ll explore how to view and modify file permissions and ownership on a Linux system. You’ll learn to inspect permission bits, change owners and groups, and apply both symbolic and numeric modes with chmod, chown, and chgrp.

Inspect Current Ownership and Permissions

Run ls -l to display the owner, group, and permission bits for files and directories:

$ ls -l
-rw-r----- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

• Owner: aaron
• Group: family
• Permissions: -rw-r-----

Only the file owner or the superuser (root) can change these settings.

Viewing and Changing Group Ownership

Use chgrp to assign a file or directory to a different group you belong to:

# Syntax: chgrp <group_name> <file_or_directory>
$ chgrp wheel family_dog.jpg
$ ls -l
-rw-r----- 1 aaron wheel 49 Oct 27 14:41 family_dog.jpg

Check your group memberships with:

$ groups
aaron wheel family

Changing File Owner with chown

Only root can change file owners. Prefix with sudo if necessary:

# Syntax: sudo chown <user>[:<group>] <file_or_directory>
$ sudo chown jane family_dog.jpg
$ ls -l
-rw-r----- 1 jane wheel 49 Oct 27 14:41 family_dog.jpg

# Change both owner and group in one go:
$ sudo chown aaron:family family_dog.jpg
$ ls -l
-rw-r----- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

Understanding Permission Bits

The permissions string (-rwxrwxrwx) breaks down as:

• First character: file type
  • - = regular file
  • d = directory
  • l = symbolic link
• Next nine: three triplets for owner, group, and others, each with r (read), w (write), and x (execute).

Permission Effects

• Files
  • r: view contents
  • w: modify contents
  • x: execute (scripts or binaries)
• Directories
  • r: list entries (ls)
  • w: create/delete entries
  • x: enter directory (cd)

Modifying Permissions with chmod

Use the symbolic syntax:

chmod [ugoa][+-=][rwx] <file_or_directory>

Adding Permissions

Allow the owner to write:

$ ls -l
-r--r----- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

$ chmod u+w family_dog.jpg
$ ls -l
-rw-r----- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

Removing Permissions

Remove the read bit for others:

$ chmod o-r family_dog.jpg
$ ls -l
-rw-r----- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

Setting Exact Permissions

Grant group read-only:

$ chmod g=r family_dog.jpg
$ ls -l
-rw-r----- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

$ chmod g=rw family_dog.jpg
$ ls -l
-rw-rw---- 1 aaron family 49 Oct 27 14:41 family_dog.jpg

Combining References

You can comma-separate multiple adjustments:

$ ls -l
-rw-r--r-- 1 appuser appuser 49 Oct 27 14:41 family.jpg

# Owner read/write, group read, others none
$ chmod u=rw,g=r,o= family.jpg
$ ls -l
-rw-r----- 1 appuser appuser 49 Oct 27 14:41 family.jpg

# Mix add/remove in one command
$ chmod u+rw,g-w family_dog.jpg

Numeric (Octal) Notation

To inspect the octal value, use stat:

$ stat family_dog.jpg
  Access: (0640/-rw-r-----)  Uid: ( 1000/aaron)   Gid: (   10/family)

Here owner has rw- (6), group has r-- (4), others have --- (0) → mode 640.

Alternatively, assign values: r=4, w=2, x=1:

• rwx = 4+2+1 = 7
• r-x = 4+0+1 = 5
• r-- = 4+0+0 = 4

Setting Numeric Permissions

$ chmod 755 family_dog.jpg  # rwxr-xr-x
$ chmod 640 family_dog.jpg  # rw-r-----

Further Reading

• Linux File Permissions – Official Documentation
• chmod Command Tutorial
• chown and chgrp Usage