The Tool Desk
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For a reliable remote workflow, install OpenSSH Server on the Ubuntu host, connect with an SSH client, prefer an Ed25519 key over a password, validate sshd configuration before restarting it, and run long jobs inside tmux or screen so a dropped connection does not end your work.
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Choose the way you will access the server
The correct route depends on two questions: can you physically reach the machine, and is it reachable on the network?
| Method | When to use it | Authentication | Network exposure | Recovery if something fails | Session persistence |
|---|---|---|---|---|---|
| Attached keyboard and display | You are beside the server or have a rack console | Local Ubuntu account | None | Direct access remains available | Ends when the local shell or machine ends |
| Hosting-provider web or serial console | The server is remote, but the provider exposes an out-of-band console | Provider and server credentials, depending on the service | Usually separate from the normal network path | Useful when SSH is misconfigured or the network is down | Depends on the console service |
| SSH | The server has a reachable address and an SSH service | Password, public key, or another SSH method | Encrypted network connection | Requires a local or provider console if the SSH service is broken | Use tmux or screen for disconnect-prone work |
Canonical describes OpenSSH as secure, encrypted remote control and file transfer. It replaced older tools that sent passwords in clear text, so SSH is the normal choice for routine administration across a network.
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Open a local terminal
Use the server’s attached console
Connect a keyboard and display to the Ubuntu machine, then sign in at the text login prompt. Some physical servers provide a dedicated console port; a hosting company may present the same function through a browser window or serial-console session. After login, you will normally see a prompt containing your username and hostname followed by $, such as alex@server01:$. Type a command after that symbol and press Enter; output appears on the following lines.
A local or provider console is especially important when you are changing SSH settings. If a configuration error prevents sshd from starting, this is the access path that lets you repair it without relying on SSH.
Open Terminal on Ubuntu Desktop
If the machine runs Ubuntu Desktop rather than a minimal server installation, open the Activities overview or application launcher and search for Terminal, command, prompt, or shell. Ubuntu also documents the Ctrl + Alt + T shortcut. This gives you a local shell on that desktop; it does not, by itself, open a shell on another server. To reach a different machine from it, use the SSH procedure below.
Prepare Ubuntu Server for SSH
Confirm the host and an account
You need an account that is allowed to log in and the server’s hostname or IP address. If you are using a provider, its control panel usually shows the public address and the initial account details. On a private network, use the address assigned to the Ubuntu host by that network. A DNS name works in place of an address when it resolves to the server.
Install the OpenSSH server package
Open a local or provider console on the Ubuntu host and install the service:
sudo apt install openssh-serverThe package supplies the SSH daemon that listens for incoming connections. Your client computer also needs an SSH client; OpenSSH clients are included with most Linux distributions and current macOS systems, and can be installed or enabled on other operating systems.
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Check the service before leaving the console
After installation, verify that the service is running and that the host is reachable from the client. If a firewall, cloud security rule, router, or provider access-control list blocks the SSH port, the daemon can be healthy while remote connections still fail. Keep the console session open until you have completed a successful SSH login from another computer.
Connect from another computer with SSH
Run the basic connection command
On the client, use the account name and the server’s hostname or address:
ssh username@server-addressReplace both values with your own details. If the server accepts the connection, SSH may ask you to confirm its host key the first time. Verify that the address is the server you intended to reach before accepting it. You will then be prompted for the account’s password unless key authentication is already configured.
A successful login changes your local command prompt to the remote account and hostname. Commands you type now execute on Ubuntu Server, not on the client computer. Run hostname or pwd if you need a quick reminder of where the shell is operating.
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Specify a non-default port
If the administrator has configured SSH to listen on a port other than the default, pass that port with -p:
ssh -p 2222 username@server-addressThe port number must match the daemon’s listening configuration and every intervening firewall rule. Changing a port does not replace authentication or encryption; it only changes where the client attempts to connect.
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End a session safely
When finished, type exit or press Ctrl + D. The remote shell closes and you return to the client prompt. Closing a terminal window has the same effect, but it can interrupt a command that is still running unless that command is inside a multiplexer session.
Use public-key authentication
Why keys are useful
SSH supports passwords, public keys, and other authentication methods. With public-key authentication, the private key remains on your client and the matching public key is placed in the server account’s ~/.ssh/authorized_keys file. The server can verify possession of the private key without receiving that private key.
Ubuntu recommends Ed25519 keys because they use a shorter key size and require fewer computational resources than older approaches. Generate one on the client with:
ssh-keygen -t ed25519Accept the suggested file location unless you have a reason to keep several keys separate. Protect the private-key file with a passphrase; the public half has a .pub suffix and is the part that belongs on the server.
Install the public key on the server
With password login temporarily available, copy the public key to the target account:
ssh-copy-id username@target_machineSign in again using ssh username@target_machine. The client should offer the Ed25519 key and ask for its passphrase rather than the server account password. If you generated the key under a custom filename, tell SSH which identity to use with -i:
ssh -i ~/.ssh/my_server_key username@target_machineNever copy or paste the private key into the server, a ticket, or a chat message. Only the public key belongs in authorized_keys.
Understand and edit SSH configuration without locking yourself out
Know where settings live
Ubuntu’s main SSH daemon configuration is /etc/ssh/sshd_config. Additional snippets can be stored in /etc/ssh/sshd_config.d/. A setting in an included snippet can affect the final configuration just as a line in the main file can, so inspect both locations when diagnosing an unexpected behavior.
Keep a recovery path open
Do not close your working SSH connection while changing remote-access settings. Keep a second session or a local/provider console available. A typo, an invalid directive, a disabled authentication method, or an incorrect port can stop sshd from starting or prevent every new login.
Validate before restarting
After editing a configuration file, test its syntax first:
sudo sshd -tNo output generally means the syntax check passed. If an error is printed, correct the reported file or line and run the test again. Only after a clean test should you restart the service:
sudo systemctl restart ssh.serviceTest a new SSH login before ending the old one. If the new connection fails, use the still-open session or the provider console to restore the last known-good configuration.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Keep work running through an SSH disconnect
Start a tmux session
A network interruption normally closes the interactive shell, but commands running inside a terminal multiplexer can continue. Ubuntu’s terminal-multiplexer documentation notes that tmux is pre-installed on Ubuntu Server.
- Connect to the server with SSH.
- Start a named session:
tmux new -s maintenance - Run your update, build, backup, or server-management commands inside that session.
- Detach without stopping the work by pressing
Ctrl+B, thenD. - If SSH disconnects, reconnect and list sessions:
tmux ls - Reattach to the existing session:
tmux attach -t maintenance
The same principle works with screen. Use one multiplexer consistently so you know which command set to use when reconnecting. A multiplexer preserves the process and terminal state; it does not make a failed command succeed or protect data that the command itself did not save.
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Read the complete manual
For the authoritative reference for a command, run:
man commandFor example, man ssh documents SSH client options and man tmux documents multiplexer behavior. Press q to leave the manual viewer.
Get a concise option list
Most command-line programs provide a shorter summary:
command --helpThis is useful when you know what a command does but need to confirm an option quickly.
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If you know the concept but not the command name, search the manual database:
man -k keywordUbuntu’s command-line guidance also covers foundational navigation commands such as pwd (print the current directory), ls (list directory contents), and cd (change directory). Start with those before running unfamiliar administrative commands, and read the relevant manual page first.
Troubleshoot common access failures
| What you see | Likely area to check | Safe next action |
|---|---|---|
| Connection timed out | The address is wrong, the host is offline, or a firewall/router/provider rule blocks the SSH port | Confirm the address and port from the provider or local network, then use the console to verify the host and service |
| Connection refused | No SSH daemon is listening on the target port, or a local rule rejects it | Open the local/provider console, install or start OpenSSH Server, and check the configured port |
| Permission denied | Wrong username, password, key, or account authorization | Confirm the account name, retry the intended key, and check that its public half is in the account’s authorized_keys |
| Host-key warning | The client has a stored key for that address that does not match the server’s current key | Stop and verify the server identity through a trusted console or administrator before accepting a replacement |
| SSH stopped accepting logins after an edit | Invalid syntax or an authentication/port setting that prevents new sessions | Use the existing session or provider console, run sudo sshd -t, fix the reported problem, then restart ssh.service |
| Long command vanished after disconnect | The command was running in the ordinary interactive shell | Reconnect and use a tmux or screen session for future long-running work |
A safe first-login workflow
Use this sequence whenever you receive a new Ubuntu Server:
Quick Recap
- Record the hostname or address, account name, and the available local or provider-console method.
- Open the console and install OpenSSH Server with
sudo apt install openssh-serverif it is not already present. - From a separate computer, connect with
ssh username@server-address. - Confirm that the shell prompt identifies the intended host.
- Generate an Ed25519 key on the client with
ssh-keygen -t ed25519and install it usingssh-copy-id username@target_machine. - Open a second key-authenticated session while the first remains available.
- For any SSH configuration change, edit the appropriate file, run
sudo sshd -t, restart withsudo systemctl restart ssh.service, and verify a new login before closing the old session. - Start
tmuxbefore updates, builds, backups, or other jobs that must survive a dropped connection.
What to remember
- Local keyboard/display access and SSH are the two practical ways to reach an Ubuntu Server terminal.
- SSH needs an OpenSSH server on the Ubuntu host and an SSH client on the computer you are using.
- Ed25519 public-key authentication keeps the private key on the client and places only the public key in
~/.ssh/authorized_keys. - Always run
sudo sshd -tbefore restarting SSH after an edit, and retain a console-based recovery path. - Use
tmuxorscreenwhen an unstable connection must not interrupt the work. - Use
man,--help, andman -kto investigate commands instead of guessing options.
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