Users and Permissions

# Create user with home directory
adduser username

# Non-interactive version
useradd -m -s /bin/bash username
passwd username

# Delete user but keep home
userdel username

# Delete user and their home directory
userdel -r username

cat /etc/passwd | grep -v nologin | grep -v false

# Debian/Ubuntu
usermod -aG sudo username

# CentOS/AlmaLinux
usermod -aG wheel username

su - username
sudo whoami
# should respond: root

nano /etc/sudoers.d/username

ls -la /path/file

# Numeric (most common)
chmod 755 file       # rwxr-xr-x: public directory
chmod 644 file       # rw-r--r--: text file
chmod 600 file       # rw-------: private file (SSH keys)
chmod 777 file       # rwxrwxrwx: all permissions (avoid!)

# Symbolic
chmod u+x script.sh     # Add execute to owner
chmod g-w file.txt      # Remove write from group
chmod o-r file.txt      # Remove read from others

# Recursive (entire folder)
chmod -R 755 /var/www/html/

# Change owner and group
chown www-data:www-data file.html

# Recursive
chown -R www-data:www-data /var/www/html/

# Typical configuration for a website with Nginx/Apache
chown -R www-data:www-data /var/www/mysite/
find /var/www/mysite/ -type d -exec chmod 755 {} \;
find /var/www/mysite/ -type f -exec chmod 644 {} \;

# Create a group
groupadd groupname

# Add user to a group
usermod -aG groupname user

# See user's groups
groups username

# See all groups
cat /etc/group