SSH

Connect to remote host

$ ssh <username>@<hostname/ip> [-p <port>]

Setup keys (no password login)
- Generate keys on client
```
$ ssh-keygen -t ed25519  -f ~/.ssh/<key-name> -C "<Some comment>"
```
  where,
  t = type of key algo
  f = file name of generated keys
  C = comment regarding who and where of key usage
- Ensure passphrase is entered, it is remembered later
- Copy public key to remote server
```
$ ssh-copy-id  -i ~/.ssh/<key-name>.pub <username>@<hostname>
```
  where,
  i = Identity file to use
- Turn off password authentication on remote server
```
$ sudo sed -i \
  -e 's/#\?PasswordAuthentication yes/PasswordAuthentication no/' \
  -e 's/PubkeyAuthentication no/PubkeyAuthentication yes/' \
  /etc/ssh/sshd_config
```
- May also disable PermitRootLogin
- May change default port
- Reload ssh daemon via systemctl sudo systemctl reload sshd
- May change default ssh porto
- Should use tool like fail2ban to reject unauthorized attempts
- To disable login banner/info:
```
$ sed -i 's/PrintLastLog yes/PrintLastLog no/' /etc/ssh/sshd_config
$ touch /home/$USER/.hushlogin
```

Add a known host to ssh config for easier connection (also used by scp & rsync), using ssh config

$ touch ~/.ssh/config && chmod 600 ~/.ssh/config

Host server-name # server-name is pattern matched
  HostName <hostname/ip> # indentation optional but recommended
  User <username>
  Port <port>
  PreferredAuthentications publickey
  IdentityFile ~/.ssh/<private-key>

$ ssh server-name

Recommended - generate a new ssh key pair for every remote host (so even if stolen, cannot compromise others). Can add in config as:
```
Host name1
  ...
  Identity ~/.ssh/<key-name>

Host name2
  ...
  Identity ~/.ssh/<key-name>
```

Running local scripts on remote host

ssh user@server 'bash -s' <<'EOF'
# ...commands
whoami
EOF