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Starting an SSH Session and Transferring Files with SCP in Ubuntu ​

This guide demonstrates how to establish an SSH connection to a remote Ubuntu server and transfer files using SCP (Secure Copy Protocol) within the same SSH session.

Prerequisites ​

  • Ubuntu operating system (local machine)
  • Access credentials (username and password or SSH key) for the remote server
  • SSH client installed (pre-installed in Ubuntu)

Step 1: Connecting to a Remote Server via SSH ​

SSH (Secure Shell) allows you to securely connect to a remote server to perform commands.

Basic SSH Connection ​

bash
ssh username@remote_server_ip

Example:

bash
ssh admin@192.168.1.100

To connect to a server using a specific port (if not using the default port 22):

bash
ssh -p port_number username@remote_server_ip

Example:

bash
ssh -p 2222 admin@192.168.1.100

Using SSH Keys for Authentication ​

If you have an SSH key for passwordless authentication:

bash
ssh -i /path/to/private_key username@remote_server_ip

Example:

bash
ssh -i ~/.ssh/id_rsa admin@192.168.1.100

Step 2: Transferring Files Using SCP ​

SCP allows secure file transfers between hosts over an SSH connection.

Transferring a Single File to Remote Server ​

bash
scp /path/to/local/file username@remote_server_ip:/path/to/remote/directory/

Example:

bash
scp ~/Documents/report.pdf admin@192.168.1.100:/home/admin/documents/

Transferring a Directory to Remote Server ​

To transfer an entire directory, use the -r (recursive) option:

bash
scp -r /path/to/local/directory username@remote_server_ip:/path/to/remote/directory/

Example:

bash
scp -r ~/Projects/website admin@192.168.1.100:/var/www/

Transferring Files from Remote Server to Local Machine ​

To download files from the remote server:

bash
scp username@remote_server_ip:/path/to/remote/file /path/to/local/directory/

Example:

bash
scp admin@192.168.1.100:/home/admin/logs/server.log ~/Downloads/

Advanced SCP Options ​

Preserving file attributes:

bash
scp -p /path/to/local/file username@remote_server_ip:/path/to/remote/directory/

Limiting bandwidth usage (e.g., to 1000 Kilobits/second):

bash
scp -l 1000 /path/to/local/file username@remote_server_ip:/path/to/remote/directory/

Compress data during transfer:

bash
scp -C /path/to/local/file username@remote_server_ip:/path/to/remote/directory/

Step 3: Using SFTP for Interactive File Transfers ​

For an interactive file transfer session:

bash
sftp username@remote_server_ip

SFTP commands:

  • put localfile - Upload a file
  • get remotefile - Download a file
  • ls - List directory contents
  • cd directory - Change directory
  • pwd - Show current directory
  • mkdir directory - Create directory
  • exit - Close the connection

Step 4: Using SSH and SCP in the Same Session ​

Method 1: Use SCP After SSH Session ​

  1. First, connect via SSH:

    bash
    ssh admin@192.168.1.100

  2. Complete your SSH tasks, then exit the SSH session:

    bash
    exit

  3. Use SCP to transfer files:

    bash
    scp ~/Documents/config.json admin@192.168.1.100:/etc/myapp/

Method 2: Use SSH to Execute SCP Remotely ​

While connected via SSH, you can initiate file transfers from the remote server:

bash
# From local machine
ssh admin@192.168.1.100

# Now on remote server, pull files from another server
scp user@another-server:/path/to/file /path/on/current/server/

# Or push files to another server
scp /local/path/file user@another-server:/remote/path/

Method 3: Using SSH Tunneling for File Transfer ​

You can create an SSH tunnel and perform file operations through it:

bash
ssh -L 8000:localhost:8000 username@remote_server_ip

Then use a web browser or other tools to access localhost:8000 for file operations.

Troubleshooting ​

  • Permission Denied: Ensure you have the correct permissions on both the source and destination.

    bash
    chmod 600 ~/.ssh/id_rsa  # For key-based authentication

  • Connection Timed Out: Check network connectivity and firewall settings.

    bash
    ping remote_server_ip

  • Host Key Verification Failed: If you've reconnected to a server with a changed host key:

    bash
    ssh-keygen -R remote_server_ip

  • "Load key '/path/to/key': error in libcrypto": This error typically occurs due to:

    1. Incorrect key format or corruption: The SSH key file may be corrupted or in an unsupported format
    2. OpenSSL library issues: There might be a mismatch between the OpenSSL version used to create the key and the one trying to read it
    3. Permissions issues: The key file permissions may be too open

    Solutions:

    bash
    # Fix permissions (most common solution)
chmod 600 ~/.ssh/id_rsa

# Check the key format
ssh-keygen -l -f ~/.ssh/id_rsa

# If needed, regenerate the key
mv ~/.ssh/id_rsa ~/.ssh/id_rsa.old
ssh-keygen -t rsa -b 4096

# Ensure correct OpenSSL libraries are installed
sudo apt update
sudo apt install --reinstall openssl libssl-dev

Best Practices ​

  1. Use SSH keys instead of passwords for improved security
  2. Keep your SSH client and server software updated
  3. Consider using rsync for synchronizing directories with many files
    bash
    rsync -avz ~/local/directory/ username@remote_server_ip:/remote/directory/
  4. Use SSH config file to simplify connections:
    bash
    # In ~/.ssh/config
Host myserver
    HostName 192.168.1.100
    User admin
    Port 22
    IdentityFile ~/.ssh/id_rsa

# Then connect with:
ssh myserver
# Or transfer files with:
scp myfile.txt myserver:/remote/path/

With these commands and techniques, you can efficiently manage remote server connections and file transfers in Ubuntu.