Allow only one command for SSH connection

For example to allow only managing processes, just add

command="htop" ssh-rsa AAAAB3NzaC1yc2E (...)

at the beginning of selected public key in ~/.ssh/authorized_keys

If you want to be extra safe, use following options:

command="htop",no-port-forwarding,no-agent-forwarding,no-X11-forwarding,no-pty ssh-rsa AAAAB3NzaC1yc2E (...)