Dropbear is a Lightweight SSH server. You can use it as openssh server alternative. Dropbear is particularly useful for embedded type Linux systems, such as wireless routers.
I have used this when I have a problem with openssh server, after an apt upgrade, openssh server stopped working. I installed dropbear and made it run on an alternative port, so I can debug openssh server problem without worrying about disconnecting from the server.
To install dropbear on Ubuntu, run
apt install dropbear
Dropbear SSH configuration
Let’s change SSH port to non default port by editing the file
vi /etc/default/dropbear
Find
DROPBEAR_PORT=22
Replace 22 with your custom port, I will use port 2222
DROPBEAR_PORT=2222
Find
NO_START=1
Replace with
NO_START=0
That completes the basic dropbear ssh configuration.
Using Dropbear SSH Server
Let’s restart dropbear service with
systemctl restart dropbear
Verify dropbear is working with command
ss -lntp | grep dropbear
As you can see dropbear is listening on port 2222. You will be able to login to the server using the custom port
ssh -p 2222 user@IP_ADDR
See SSH