List set and change standard file permissions

Managing file permissions is a core skill for any Linux administrator or user. In this guide, you’ll learn how to view ownership, adjust user and group assignments, interpret permission bits, and modify permissions using both symbolic and octal notation.

Table of Contents

1. Understanding Ownership
2. Viewing Owner, Group, and Permissions
3. Changing Owner and Group
4. File Types and Permission Bits
5. Permission Evaluation Order
6. Modifying Permissions with chmod
   • Adding Permissions
   • Removing Permissions
   • Setting Exact Permissions
   • Combining Multiple Changes
7. Using Octal Notation with chmod
8. Resources & References

Understanding Ownership

Every file or directory on Linux has:

• User owner (UID)
• Group owner (GID)

Only the file’s owner or root can change its permissions or ownership.

Viewing Owner, Group, and Permissions

Run ls -l to display permissions, owner, group, size, and timestamp:

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

• -rw-r-----: File type and permission bits
• aaron   : User owner
• family   : Group owner

Changing Owner and Group

Change Group: chgrp

$ chgrp wheel family_dog.jpg

Example:

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

$ chgrp wheel family_dog.jpg

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

$ groups
aaron wheel family

Change Owner: chown

Only root (or via sudo) can change the user owner:

$ sudo chown jane family_dog.jpg

Example:

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

$ sudo chown jane family_dog.jpg

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

You can change both user and group:

$ sudo chown aaron:family family_dog.jpg

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

File Types and Permission Bits

The first character in ls -l indicates the file type:

Permission bits follow in three sets (owner, group, others):

[!note] For directories:

• r: list contents
• w: create/delete files
• x: change into the directory

Permission Evaluation Order

Linux checks permissions in this order:

1. Owner
2. Group
3. Others

Consider a file owned by aaron:family with permissions -r--rw----:

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

• As aaron: owner bits (r--) apply → no write

  $ echo "Update" >> family_dog.jpg
  bash: family_dog.jpg: Permission denied
  

• As jane (in family): owner bits skipped, group bits (rw-) apply → can write

  $ su jane
  $ echo "Add this content" >> family_dog.jpg
  $ cat family_dog.jpg
  Picture of Milo the dog
  

• Else: “others” bits determine access.

Modifying Permissions with chmod

General syntax:

chmod [who][+|-|=][perms] file

• who: u (owner), g (group), o (others), a (all)
• +: add permissions
• -: remove permissions
• =: set exact permissions

Adding Permissions

Grant write to owner:

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

$ chmod u+w family_dog.jpg

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

Removing Permissions

Use - to revoke bits. Common patterns:

Remove read for others:

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

$ chmod o-r family_dog.jpg

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

Setting Exact Permissions

Overwrite existing bits with =:

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

$ 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

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

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

Combining Multiple Changes

Separate specs with commas:

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

# Owner: add read/write, Group: set to read-only, Others: remove all
$ chmod u+rw,g=r,o= family_dog.jpg

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

Using Octal Notation with chmod

Octal mode is a compact way to set permissions. First, inspect with stat:

$ stat family_dog.jpg
  File: family_dog.jpg
  Size: 49            Blocks: 8    IO Block: 4096   regular file
Device: fd00h/64768d  Inode: 52946177 Links: 1
Access: (0640/-rw-r-----)  Uid: ( 1000/aaron) Gid: (   10/wheel)

[!note] Each octal digit = read (4) + write (2) + execute (1).
For 0640:

• Owner 6 = rw-
• Group 4 = r--
• Others 0 = ---

Set 0640 directly:

$ chmod 640 family_dog.jpg

Resources & References

• Linux Permissions Handbook
• chmod Manual
• Kubernetes Basics