Users & Groups

1. Users and Group Management

Creating Users and Groups

• Add User: sudo adduser username
• Add Group: sudo addgroup groupname

Modifying Users and Groups

• Add User to Group: sudo adduser username groupname
• Change User's Primary Group: sudo usermod -g groupname username

2. Permissions and Ownership

Every file and directory in Linux has associated access rights, which are defined by the file's owner, the group, and others.

Viewing Permissions

• List with Permissions: ls -l

Modifying Permissions

• Change Permissions: chmod 755 filename

Changing Ownership

• Change Owner: chown username:groupname filename

File Permissions and Ownership

• Change file permissions. chmod 755 script.sh
• Change file owner and group. chown user:usergroup file.txt
• Change the group of a file. chgrp newgroup file.txt

Special Permissions

• setuid on an executable file: chmod u+s /path/to/executable
• setgid on a directory: chmod g+s /path/to/directory
• Sticky bit on a directory: chmod +t /path/to/directory

Permissions Numeric System Example

• Give read, write, and execute permissions to the owner, read and execute to the group, and only read to others: chmod 754 file.txt