How do you create, modify, and delete users in Linux?

Create with useradd, change with usermod, remove with userdel, set the password with passwd — and always use usermod -aG (with the -a) when adding someone to a group.

The single biggest gotcha lives in usermod -G: without -a it replaces the user's entire supplementary group list, silently dropping them from every other group (including wheel/sudo). The -a means "append", which is almost always what you want.

User management commands:

Create user:

sudo useradd -m -g groupname username
sudo useradd -u 1221 -g student -s /bin/bash -c "Full Name" username

useradd options:

Modify user:

# Add to group (append!)
sudo usermod -aG wheel username
sudo usermod -d /new/home username # Change home directory
sudo usermod -L username           # Lock account
sudo usermod -U username           # Unlock account

Delete user:

sudo userdel username        # Delete user (keep files)
sudo userdel -r username     # Delete user AND home directory

Important: Use -a with -G to APPEND groups. Without -a, existing groups are replaced!