Linux Setup

First-boot setup snippets for fresh Linux hosts — creating an admin user and getting SSH keys in place.

Arch Linux — Add an Admin User

# -m creates the home directory; set a password after
useradd -m alice
passwd alice
 
# Add to the wheel group (sudoers). Flags first, then group, then user.
usermod -aG wheel alice
 
# Give wheel sudo rights: run visudo and uncomment the wheel line
pacman -S vi          # visudo ships with the base system / sudo package
EDITOR=vi visudo      # uncomment: %wheel ALL=(ALL:ALL) ALL

usermod argument order

usermod -aG <group> <user> — -a appends (without it the user is removed from every other supplementary group), -G names the group(s). The user always comes last.

VPS: copy your SSH key to the new user

When bootstrapping a VPS where you logged in as root, copy root’s authorized key over to the new user so key auth works immediately:

rsync --archive --chown=alice:alice ~/.ssh /home/alice/

Debian / Ubuntu — Add an Admin User

adduser alice                 # interactive: creates home + prompts for password
usermod -aG sudo alice        # 'sudo' group instead of Arch's 'wheel'

Related

Harden the SSH daemon after setup — see SSH - Snippets for key generation and SSH - Mac OS for a hardened sshd_config.