SSH

# Restart client (macOS)
$ eval "$(ssh-agent -s)"
# Restart server (Linux)
$ sudo systemctl restart sshd

# Create a new key (macOS)
$ ssh-keygen -t ed25519 -C <EMAIL>
$ ssh-add --apple-use-keychain <path/to/key>
$ eval "$(ssh-agent -s)"

# Copy key to remote server
$ ssh-copy-id -i <path/to/key> <user>@<server>

# /etc/ssh/sshd_config settings:
#  PermitRootLogin no
#  PermitRootLogin without-password
#  PasswordAuthentication no

# Print settings
$ sshd -T

# Logs
$ less /var/log/auth.log
$ cat /var/log/auth.log | grep 'New session [0-9]\+ of user [a-z]\+'

# Fix SELinux context
$ restorecon -R -v /home/$USER/.ssh