Bash

🔐 chmod – Modify File Permissions

Syntax:

chmod [OPTIONS] MODE FILE

Permission Values:

Symbolic	Numeric	Meaning
r	4	Read
w	2	Write
x	1	Execute

Common Usage:

Mode	Description
755	rwxr-xr-x (owner all, others read/exec)
644	rw-r–r– (owner read/write)
700	rwx—— (private)

Examples:

chmod 755 script.sh
chmod +x file.sh            # Add execute permission
chmod -x file.sh            # Remove execute
chmod u+x file.sh           # Add exec to owner
chmod g-w file.txt          # Remove write from group

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👤 chown – Change File Owner

Syntax:

chown [OPTIONS] OWNER[:GROUP] FILE

Options:

Option	Description
-R	Recursive
-v	Verbose output

Examples:

chown user file.txt
chown user:group file.txt
chown -R newuser /home/newuser/

You must be root or use sudo to change ownership.

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👥 chgrp – Change Group Ownership

Syntax:

chgrp [OPTIONS] GROUP FILE

Options:

Option	Description
-R	Apply recursively
-v	Verbose mode

Examples:

chgrp developers script.sh
chgrp -R teamgroup /var/www/

Useful when multiple users share a group for project files.

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🔑 Understanding File Ownership in Linux

Each file or directory in Linux has:

• Owner: The user who owns the file.
• Group: The group associated with the file.
• Others: Everyone else.

View Ownership:

ls -l

Example output:

-rw-r--r-- 1 alice developers 1024 Jul 3 file.txt

• alice is the owner
• developers is the group

Change Ownership:

chown newuser file.txt

Change Group:

chgrp newgroup file.txt

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