$ launchctl list | grep ssh
-   0   com.openssh.ssh-agent
$ ps -A | grep ssh
1483 ??         0:00.00 ssh-agent -s
8483 ??         0:00.00 ssh-agent

$ sudo launchctl unload /System/Library/LaunchDaemons/ssh.plist
$ sudo launchctl load -w /System/Library/LaunchDaemons/ssh.plist

$ sudo launchctl stop com.openssh.sshd
$ sudo launchctl start com.openssh.sshd

$ eval `ssh-agent -s`
Agent pid 9055

$ /usr/sbin/sshd -d
debug1: sshd version OpenSSH_7.9, LibreSSL 2.7.3
Could not load host key: /etc/ssh/ssh_host_rsa_key
Could not load host key: /etc/ssh/ssh_host_ecdsa_key
Could not load host key: /etc/ssh/ssh_host_ed25519_key
sshd: no hostkeys available -- exiting.