SSH / SCP / rsync

Usage of SSH, SCP and rsync

Generate key

From Create ed25519 key

ed25519

ssh-keygen -t ed25519 -b 4096 -C "user@mail"

ed25519 (no mail)

ssh-keygen -t ed25519

rsa

ssh-keygen -t rsa -b 2048

Add to server

Connect to your remote server and add your public key to ~/.ssh/authorized_keys.

vim ~/.ssh/authorized_keys

ssh-ed25519 AAAAC3Nza...

~/.ssh/authorized_keys

And add your id_ed25519.pub or id_rsa.pub.

Exit your remote server and try SSH connection.

Usage

INFO

To find your IP address, you can use:

ip a | grep glo | awk '{print $2}' | head -1 | cut -f1 -d/

Here, user is your username, hostname is your server hostname or IP address.

ssh <user>@<hostname>

If it works, you can disable password authentication.

Disable password authentication

You can disable password authentication by editing the /etc/ssh/sshd_config file on your server.

vim /etc/ssh/sshd_config

Change the PasswordAuthentication option:

PasswordAuthentication yes
PasswordAuthentication no

/etc/ssh/sshd_config

Restart the SSH service:

systemctl restart sshd

Use different port

By default, SSH uses port 22. You can change it by editing the /etc/ssh/sshd_config file on your server.

vim /etc/ssh/sshd_config

Change the port number:

Port 22
Port 23

/etc/ssh/sshd_config

Restart the SSH service:

systemctl restart sshd

Firewall

Don't forget to open the port in your server firewall. If you use UFW, you can use:

ufw allow <port>

And check the status:

ufw status

You can delete old port:

ufw delete allow <old port>

fail2ban

If you use fail2ban, you need to add the new port to the configuration.

vim /etc/fail2ban/jail.local

[sshd]
port = <port>

/etc/fail2ban/jail.local

And restart the service:

systemctl restart fail2ban

To use SSH on a different port, you need to specify the port number when connecting.

ssh -p <port> <user>@<hostname>

Use different private key

By default, SSH uses ~/.ssh/id_ed25519 or ~/.ssh/id_rsa as private key. You can use different private key by using -i option.

ssh -i <private key filename> <user>@<hostname>

You can use -o option to specify IdentitiesOnly to prevent SSH from trying other authentication methods.

ssh -o "IdentitiesOnly=yes" -i <private key filename> <user>@<hostname>

SSH config

You can create a ~/.ssh/config file to store your SSH configuration.

vim ~/.ssh/config

• Host is the alias you want to use to connect to your server.
• HostName is the IP address or hostname of your server.
• User is your username.
• Port is the port number.
• IdentityFile is the path to your private key.
• IdentitiesOnly is set to yes to prevent SSH from trying other authentication methods.

Host <myserver>
  HostName <hostname_or_ip_address>
  User <username>
  Port <port>
  IdentityFile <private key filename path>
  IdentitiesOnly yes

~/.ssh/config

Now you can connect to your server using the alias.

ssh <myserver>

SSH config example

Host my-wonderful-server
  HostName 123.456.789.0
  User unicorn_admin
  Port 22
  IdentityFile ~/.ssh/id_ed25519
  IdentitiesOnly yes

Host my-other-wonderful-server
  HostName 123.456.789.1
  User panda_admin
  Port 23
  IdentityFile ~/.ssh/id_rsa
  IdentitiesOnly yes

~/.ssh/config

ssh my-wonderful-server

SCP

SCP is a command-line utility that allows you to securely copy files and directories between two locations. This command use same authentication method as SSH.

Tutorial

From server to personal computer

scp username@from_host:file.txt /local/directory/

From personal computer to server

scp file.txt username@to_host:/remote/directory/

Use different SSH port

From server to personal computer

scp -P <port> username@from_host:file.txt /local/directory/

From personal computer to server

scp -P <port> file.txt username@to_host:/remote/directory/

rsync

Good alternative to SCP, rsync is a fast and versatile command-line utility for synchronizing files and directories between two locations over a remote shell, or from/to a remote rsync daemon. It uses an algorithm that minimizes the amount of data copied by only moving the portions of files that have changed.

rsync -Phhr username@server:/home/path/to/dir ./

• -P for progress
• -hh for human human readible
• -r for recursive

Use different SSH port

rsync -Phhr -e 'ssh -p <port>' username@server:/home/path/to/dir ./