enable sshd
By default, sshd is disabled on ubuntu desktop. Therefore you need to install & enable sshd if you would like to access host remotely via ssh.
Here is short memo for this sake.
First, search for sshd package via apt-cache command.
$ sudo apt-cache search sshd
openssh-server - secure shell (SSH) server, for secure access from remote machines
$ sudo apt-cache show openssh-server
Package: openssh-server
...
Description-en: secure shell (SSH) server, for secure access from remote machines
...
This package provides the sshd server.
OK, openssh-server seems to be what we are looking for.
$ sudo apt-get install openssh-server
Installation will automatically start sshd daemon.
$ sudo lsof -nPi:22
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
sshd 3557 root 3u IPv4 35564 0t0 TCP *:22 (LISTEN)
sshd 3557 root 4u IPv6 35566 0t0 TCP *:22 (LISTEN)
$ sudo service ssh status
ssh start/running, process 3557
Please be noted, sshd daemon is registered not as sshd but as ssh.
sshd configuration can be set in /etc/ssh/sshd_config. In case that you would like to disable remote root access, then change parameter PermitRootLogin value from yes to no.
PermitRootLogin no