How to connect to a server with the ssh command - Rocketeers app

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How to connect to a server with the ssh command
===============================================

### [\#CommandLine](https://rocketeersapp.com/knowledge/command-line)

Connect to a remote server with the ssh command, including custom ports, key files, the host key prompt, SSH config aliases, and verbose debugging.

 Published by [Mark van Eijk](https://rocketeersapp.com/author/mark-van-eijk) on June 23, 2026 · 2 minute read

1. [Connecting with ssh](#content-connecting-with-ssh)
2. [Custom port](#content-custom-port)
3. [Using a specific key file](#content-using-a-specific-key-file)
4. [The first-connection prompt](#content-the-first-connection-prompt)
5. [Host aliases with ~/.ssh/config](#content-host-aliases-with-sshconfig)
6. [Debugging with -v](#content-debugging-with--v)
7. [Where to go next](#content-where-to-go-next)

[\#](#content-connecting-with-ssh "Permalink")Connecting with ssh
-----------------------------------------------------------------

SSH is how I reach almost every server I work with. The basic form is the command, the user, and the host:

 ```
ssh jane@203.0.113.10

```

You can use a hostname instead of an IP, and SSH will resolve it:

 ```
ssh jane@app.example.com

```

If you don't pass a key explicitly, SSH tries the default keys in `~/.ssh`. If you don't have a key yet, generate one first: [create SSH keys with ssh-keygen](/generate-ssh-keys-ssh-keygen).

[\#](#content-custom-port "Permalink")Custom port
-------------------------------------------------

SSH listens on port 22 by default. Many servers move it elsewhere for security. Use `-p` (lowercase) to specify the port:

 ```
ssh -p 2222 jane@app.example.com

```

[\#](#content-using-a-specific-key-file "Permalink")Using a specific key file
-----------------------------------------------------------------------------

Cloud providers often hand you a `.pem` file. Point SSH at it with `-i` (identity file):

 ```
ssh -i ~/.ssh/aws-key.pem ubuntu@203.0.113.10

```

If the key has loose permissions, SSH refuses to use it. Fix it with `chmod 400 ~/.ssh/aws-key.pem` so only you can read it.

[\#](#content-the-first-connection-prompt "Permalink")The first-connection prompt
---------------------------------------------------------------------------------

The first time you connect to a host, SSH shows the server's fingerprint and asks:

 ```
The authenticity of host 'app.example.com' can't be established.
ED25519 key fingerprint is SHA256:abc123...
Are you sure you want to continue connecting (yes/no/[fingerprint])?

```

Type `yes` and SSH stores the fingerprint in `~/.ssh/known_hosts`. On later connections it checks silently. This is expected; it only warns you again if the fingerprint changes.

[\#](#content-host-aliases-with-sshconfig "Permalink")Host aliases with ~/.ssh/config
-------------------------------------------------------------------------------------

Typing long commands gets old fast. I keep a `~/.ssh/config` so I can connect with a short alias:

 ```
Host prod
    HostName app.example.com
    User jane
    Port 2222
    IdentityFile ~/.ssh/aws-key.pem

```

Now the whole thing collapses to:

 ```
ssh prod

```

Every flag above can live in the config, which keeps it out of your muscle memory and your shell history.

[\#](#content-debugging-with--v "Permalink")Debugging with -v
-------------------------------------------------------------

When a connection misbehaves, `-v` (verbose) shows exactly what SSH is doing: which keys it offers, what the server accepts, and where it stops. Add more `v`s for more detail:

 ```
ssh -v prod
ssh -vvv prod

```

If you hit `Permission denied (publickey)`, I've written up the causes and fixes here: [SSH permission denied (publickey)](/ssh-permission-denied-publickey).

[\#](#content-where-to-go-next "Permalink")Where to go next
-----------------------------------------------------------

Once you can connect, you can do more than open a shell. Run a single command without a full session with [run a command over SSH](/run-command-over-ssh), and move files with [scp over SSH](/copy-files-over-ssh-scp).

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