SSH (Secure Shell) is a way to securely connect to another computer over the internet. When you “SSH into a server,” you’re opening a terminal on that remote machine and running commands as if you were sitting in front of it.

It’s how developers manage servers, deploy code, and transfer files — all encrypted so nobody can snoop on the connection.

What SSH looks like

ssh alice@192.168.1.100

This connects to the machine at 192.168.1.100 as the user alice. You get a terminal prompt on that machine and can run any command.

alice@server:~$ ls /var/www
html  my-app  backups
alice@server:~$ sudo systemctl restart nginx
alice@server:~$ exit

Type exit to disconnect.

How SSH works (simplified)

1. Your computer contacts the server: “I want to connect as alice”
2. The server says: “Prove you’re alice”
3. You prove it with either a password or an SSH key
4. An encrypted tunnel is established
5. Everything you type travels through that tunnel — encrypted

Nobody between you and the server can see what you’re doing. Not your ISP, not the coffee shop WiFi, nobody.

Passwords vs. SSH keys

Passwords — simple but weak:

• You type a password every time
• Can be brute-forced
• If someone sees you type it, they have access

SSH keys — the right way:

• You generate a key pair: a private key (stays on your computer) and a public key (goes on the server)
• The server challenges you, your private key proves your identity
• No password to type, no password to steal
• Much harder to crack than any password

# Generate a key pair
ssh-keygen -t ed25519 -C "your@email.com"

# Copy the public key to the server
ssh-copy-id alice@192.168.1.100

# Now connect without a password
ssh alice@192.168.1.100

For the full setup guide, see the SSH cheat sheet.

Common uses

Managing servers:

ssh deploy@production-server
# Check logs, restart services, debug issues

Git (GitHub, GitLab):

git clone git@github.com:user/repo.git
# Uses SSH to authenticate with GitHub

Copying files:

# Copy a file to the server
scp ./app.zip alice@server:/home/alice/

# Copy from the server
scp alice@server:/var/log/app.log ./

Port forwarding (tunnels):

# Access a remote database through an SSH tunnel
ssh -L 5432:localhost:5432 alice@server
# Now connect to localhost:5432 to reach the server's PostgreSQL

This is incredibly useful when a database isn’t exposed to the internet but you need to access it from your laptop.

The SSH config file

Instead of typing long commands, save them in ~/.ssh/config:

Host prod
    HostName 203.0.113.50
    User deploy
    IdentityFile ~/.ssh/deploy_key

Host staging
    HostName 203.0.113.51
    User deploy
    IdentityFile ~/.ssh/deploy_key

Now just type:

ssh prod
ssh staging

Common issues

• “Permission denied (publickey)” — your key isn’t on the server or has wrong permissions. See: Git permission denied fix
• “Connection refused” — the SSH server isn’t running or the port is wrong. See: ERR_CONNECTION_REFUSED fix
• “Host key verification failed” — the server’s identity changed (or you’re connecting for the first time)

SSH vs. other tools

Tool	Use case
SSH	Terminal access, tunnels, file transfer
RDP	Windows remote desktop (graphical)
VNC	Remote desktop (any OS, graphical)
Telnet	Like SSH but unencrypted (never use this)

SSH is the standard for server management. If you’re a developer, you’ll use it constantly.

Next steps

1. Generate an SSH key: ssh-keygen -t ed25519
2. Add it to GitHub: Settings → SSH Keys → paste your public key
3. Clone a repo with SSH: git clone git@github.com:user/repo.git
4. Set up an ~/.ssh/config file for servers you connect to often
5. Check out the full SSH cheat sheet for tunnels, agent forwarding, and more