scp Command Linux: Complete Guide to Secure File Transfer Over SSH

The scp (Secure Copy Protocol) command is one of the most essential tools in Linux for securely transferring files between local and remote systems over SSH. Built on top of SSH protocol, scp provides encrypted file transfers, making it the preferred choice for system administrators and developers who need to move files across networks safely.

In this comprehensive guide, we’ll explore everything you need to know about the scp command, from basic syntax to advanced usage scenarios with practical examples.

What is the scp Command?

The scp command stands for “Secure Copy Protocol” and is a network protocol that supports file transfers between hosts on a network. It uses SSH (Secure Shell) for data transfer and authentication, ensuring that your files are encrypted during transmission.

Key Features of scp:

• Encrypted transfers: All data is encrypted using SSH
• Authentication: Uses SSH keys or password authentication
• Preserves file attributes: Maintains timestamps, permissions, and modes
• Recursive copying: Can copy entire directory structures
• Cross-platform: Works between different Unix-like systems

Basic Syntax and Structure

The basic syntax of the scp command follows this pattern:

scp [options] source destination

Where:

• source – The file or directory to copy from
• destination – The location to copy to
• [options] – Various flags to modify behavior

Remote Path Format

For remote files, use the format:

[user@]hostname:path

Examples:

• [email protected]:/home/user/file.txt
• [email protected]:/var/log/
• [email protected]:/etc/nginx/nginx.conf

Essential scp Command Options

Basic File Transfer Examples

1. Copy Local File to Remote Server

scp /path/to/local/file.txt [email protected]:/path/to/destination/

Example:

scp document.pdf [email protected]:/home/john/Documents/

Expected Output:

document.pdf                          100%  245KB   2.1MB/s   00:00

2. Copy Remote File to Local System

scp [email protected]:/path/to/remote/file.txt /local/destination/

Example:

scp [email protected]:/var/log/apache2/access.log ./logs/

Expected Output:

access.log                            100%  1.2MB   890KB/s   00:01

3. Copy File Between Two Remote Servers

scp [email protected]:/path/file.txt [email protected]:/path/destination/

Example:

scp [email protected]:/backup/database.sql [email protected]:/tmp/

Directory Transfer Examples

1. Copy Directory Recursively

Use the -r flag to copy entire directories:

scp -r /local/directory/ [email protected]:/remote/path/

Example:

scp -r ./website/ [email protected]:/var/www/html/

Expected Output:

index.html                            100%   12KB   1.2MB/s   00:00
style.css                             100%    8KB   980KB/s   00:00
script.js                             100%    5KB   750KB/s   00:00
images/logo.png                       100%   45KB   2.1MB/s   00:00
images/banner.jpg                     100%  156KB   3.2MB/s   00:00

2. Preserve File Attributes

Use -p to maintain original timestamps and permissions:

scp -rp /local/backup/ [email protected]:/backups/

Advanced scp Usage

1. Using Custom SSH Port

When your SSH server runs on a non-standard port:

scp -P 2222 file.txt [email protected]:/home/user/

Note: Use capital -P for port specification (unlike ssh which uses lowercase -p).

2. Using SSH Private Key

scp -i ~/.ssh/private_key file.txt [email protected]:/home/user/

Example:

scp -i ~/.ssh/aws-key.pem application.zip [email protected]:/home/ec2-user/

3. Enable Compression for Large Files

Use -C to compress data during transfer:

scp -C large-file.tar.gz [email protected]:/tmp/

4. Verbose Output for Troubleshooting

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

Sample Verbose Output:

Executing: program /usr/bin/ssh host server.com, user user, command scp -v -t /home/user/
OpenSSH_8.0p1, OpenSSL 1.1.1c  28 May 2019
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Connecting to server.com [192.168.1.100] port 22.
debug1: Connection established.
debug1: Authentication succeeded (publickey).
file.txt                              100%    1KB     1.2KB/s   00:00

Practical Real-World Examples

1. Website Deployment

# Deploy website files to production server
scp -r ./dist/ [email protected]:/var/www/html/

# Deploy with compression for faster transfer
scp -rC ./dist/ [email protected]:/var/www/html/

2. Database Backup Transfer

# Transfer database backup to backup server
scp -C database_backup_$(date +%Y%m%d).sql [email protected]:/backups/mysql/

# Transfer with custom SSH key
scp -i ~/.ssh/backup-key -C backup.sql [email protected]:/encrypted/backups/

3. Log File Collection

# Collect application logs from multiple servers
scp app-server1.com:/var/log/app.log ./logs/app-server1.log
scp app-server2.com:/var/log/app.log ./logs/app-server2.log
scp app-server3.com:/var/log/app.log ./logs/app-server3.log

4. Configuration File Synchronization

# Sync configuration files across servers
scp -p /etc/nginx/nginx.conf [email protected]:/etc/nginx/
scp -p /etc/nginx/nginx.conf [email protected]:/etc/nginx/

Using Wildcards and Multiple Files

Transfer Multiple Files

# Multiple specific files
scp file1.txt file2.txt file3.txt [email protected]:/home/user/

# Using wildcards (quote them to prevent local expansion)
scp "*.txt" [email protected]:/home/user/documents/

# Copy all .conf files
scp /etc/nginx/*.conf [email protected]:/backup/nginx/

Security Best Practices

1. Use SSH Keys Instead of Passwords

# Generate SSH key pair
ssh-keygen -t rsa -b 4096 -C "[email protected]"

# Copy public key to remote server
ssh-copy-id [email protected]

# Use scp with key authentication
scp -i ~/.ssh/id_rsa file.txt [email protected]:/home/user/

2. Specify SSH Options

# Disable host key checking for automated scripts (use carefully)
scp -o StrictHostKeyChecking=no file.txt [email protected]:/tmp/

# Set connection timeout
scp -o ConnectTimeout=10 file.txt [email protected]:/home/user/

# Use specific cipher
scp -o Cipher=aes256-ctr file.txt [email protected]:/home/user/

Error Handling and Troubleshooting

Common Error Messages and Solutions

1. Permission Denied

scp: /remote/path/file.txt: Permission denied

Solutions:

• Check file permissions on the destination directory
• Ensure the user has write permissions
• Use sudo if necessary: scp file.txt [email protected]:/tmp/ && ssh [email protected] 'sudo mv /tmp/file.txt /root/'

2. Host Key Verification Failed

Host key verification failed.

Solutions:

• Remove old host key: ssh-keygen -R hostname
• Accept new host key manually: ssh user@hostname

3. Connection Refused

ssh: connect to host server.com port 22: Connection refused

Solutions:

• Check if SSH service is running on remote host
• Verify the correct port number
• Check firewall settings

Performance Optimization Tips

1. Use Compression for Large Files

# Enable compression
scp -C large-file.tar [email protected]:/home/user/

# For multiple files
scp -rC ./large-directory/ [email protected]:/backup/

2. Parallel Transfers

For multiple files, use parallel processing:

# Using GNU parallel (if available)
parallel -j4 scp {} [email protected]:/destination/ ::: file1.txt file2.txt file3.txt file4.txt

# Using background processes
scp file1.txt [email protected]:/dest/ &
scp file2.txt [email protected]:/dest/ &
scp file3.txt [email protected]:/dest/ &
wait

3. Optimize SSH Configuration

Add to ~/.ssh/config:

Host myserver
    HostName server.example.com
    User myuser
    Port 22
    IdentityFile ~/.ssh/my_key
    Compression yes
    ServerAliveInterval 60

Then use:

scp file.txt myserver:/home/myuser/

Automation and Scripting

Bash Script Example

#!/bin/bash
# Automated backup script using scp

SOURCE_DIR="/important/data"
REMOTE_SERVER="[email protected]"
REMOTE_PATH="/backups/daily"
DATE=$(date +%Y%m%d_%H%M%S)
BACKUP_NAME="backup_${DATE}.tar.gz"

# Create compressed backup
tar -czf "/tmp/${BACKUP_NAME}" "${SOURCE_DIR}"

# Transfer to backup server
if scp -C "/tmp/${BACKUP_NAME}" "${REMOTE_SERVER}:${REMOTE_PATH}/"; then
    echo "Backup successful: ${BACKUP_NAME}"
    rm "/tmp/${BACKUP_NAME}"
else
    echo "Backup failed!"
    exit 1
fi

Alternatives to scp

While scp is excellent for basic file transfers, consider these alternatives for specific use cases:

• rsync: Better for synchronizing files and handling interruptions
• sftp: Interactive file transfer with more features
• pscp (PuTTY): Windows equivalent of scp
• wget/curl: For downloading files from web servers

Conclusion

The scp command is an indispensable tool for secure file transfers in Linux environments. Its integration with SSH provides robust security, while its straightforward syntax makes it accessible for both beginners and advanced users. Whether you’re deploying applications, backing up data, or managing configuration files across multiple servers, mastering scp will significantly improve your workflow efficiency.

Remember to always prioritize security by using SSH keys, keeping your systems updated, and following the principle of least privilege when setting up file transfer operations. With the examples and techniques covered in this guide, you’re well-equipped to handle any file transfer scenario securely and efficiently.