Linux commands for system administrators

1. What Is SSH?

ssh enables encrypted remote shell access between Linux machines. You can remotely log in to servers and manage systems securely.

ssh user@hostname

Example:

ssh [email protected]

2. Installing SSH

• SSH client: Usually preinstalled
• SSH server: Required on destination machine

sudo apt install openssh-server

sudo systemctl enable --now ssh

3. Common SSH Options

• -p: Specify a custom port

ssh -p 2222 user@host

• -i: Use a private key for authentication

ssh -i ~/.ssh/id_rsa user@host

• -L: Setup tunneling or port forwarding

ssh -L 8080:localhost:80 user@host

4. What Is SCP?

scp copies files securely between hosts over SSH. It encrypts both credentials and file data during transfer.

5. Upload File from Local to Remote

scp file.txt [email protected]:/home/user/

6. Download File from Remote to Local

scp [email protected]:/home/user/file.txt ./

7. Copy Folders with SCP

scp -r myfolder/ user@host:/home/user/

8. Important SCP Flags

scp -P 2222 file.txt user@host:/path

scp -i ~/.ssh/id_rsa file.txt user@host:/path

scp -r dir/ user@host:/path

scp -v file.txt user@host:/path

9. Security Best Practices

• Use SSH key pairs instead of passwords (ssh-keygen)
• Place public key in ~/.ssh/authorized_keys on remote host
• Secure key permissions: chmod 600 ~/.ssh/id_rsa
• Configure firewall or fail2ban to prevent brute-force SSH attacks

10. Conclusion

ssh and scp are foundational tools for remote management and secure file transfers in Linux. Mastering them enables efficient and encrypted access between systems, strengthening both productivity and data security.