Linux File Permissions

In Linux, every file and directory has permissions that determine who can read, write, or execute the file. Each file or directory has three levels of ownership:

• User owner (u).
• Group owner (g).
• Others (o).

Each ownership level can be assigned the following permissions:

• Read (r).
• Write (w).
• Execute (x).

How to check permissions

Use the following command:

ls -l

Sample output:

-rwxr-xr--  1 user1 admin  1234 Jul  2 08:00 script.sh

Explanation of the first column -rwxr-xr--:

Character	Meaning
-	Type: - (regular file), d (directory), l (symlink), etc
rwx	Owner: read, write, execute
r-x	Group: read, no write, execute
r--	Others: read only

You can also use the stat command as follows with more complete results:

stat anaconda-ks.cfg 

Sample output:

  File: anaconda-ks.cfg
  Size: 1326            Blocks: 8          IO Block: 4096   regular file
Device: fd00h/64768d    Inode: 33575044    Links: 1
Access: (0600/-rw-------)  Uid: (    0/    root)   Gid: (    0/    root)
Context: system_u:object_r:admin_home_t:s0
Access: 2025-06-28 01:09:22.473000000 +0700
Modify: 2025-06-28 01:09:22.606000000 +0700
Change: 2025-06-28 01:09:22.606000000 +0700
 Birth: 2025-06-28 01:09:22.473000000 +0700

How to Change Permissions

Using Symbols

Add execute permission to the user (owner).

chmod u+x script.sh

Symbols:

• u = user (owner)

• g = group

• o = others

• a = all (u+g+o)

Operation:

• + = tambah izin

• - = hapus izin

• = = set izin secara eksplisit

Sample:

chmod g-w file.txt     # Clear group write permissions
chmod o=rx file.txt    # Set others can only read and execute

Using Numeric

Format: chmod XYZ nama_file Each category (user, group, other) is represented by 1 digit:

Numbers	Permissions
0	---
1	--x
2	-w-
3	-wx
4	r--
5	r-x
6	rw-
7	rwx

Sample:

chmod 755 script.sh   # rwx for user, rx for group & others
chmod 644 file.txt    # rw- for user, r-- for group & others

Change Owner and Group

Change the owner of the file:

chown username file.txt

Change the owner of files and groups:

chown user:group file.txt

Change only the group;

chgrp groupname file.txt

Default Permission

Directories usually use 755

chmod 755 /var/www

Files using 644

chmod 644 file.txt

The following permissions are commonly used:

Purpose	Meaning
Scripts can only be run by the owner	chmod 700 script.sh
The file can be read by all, but only the owner can edit	chmod 644 file.txt
Directory accessible to everyone, only owner can change contents	chmod 755 /data/public
Script .sh must execute	chmod +x script.sh