scp

Overview

The scp (secure copy) command securely transfers files between hosts over SSH. It provides encrypted file transfer with authentication and maintains file permissions and timestamps.

Syntax

scp [options] source destination
scp [options] source... destination

Common Options

Option Description
-r Recursive copy (directories)
-p Preserve timestamps and permissions
-v Verbose output
-q Quiet mode
-C Enable compression
-P port Specify SSH port
-i keyfile Use specific SSH key
-o option SSH options
-l limit Bandwidth limit (Kbit/s)
-S program SSH program to use

File Transfer Patterns

Pattern Description
file user@host:path Local to remote
user@host:file path Remote to local
user@host1:file user@host2:path Remote to remote
*.txt user@host:dir/ Multiple files

Key Use Cases

  1. Secure file transfer
  2. Remote backup
  3. Configuration deployment
  4. Log file collection
  5. Development file sync

Examples with Explanations

Example 1: Copy File to Remote

scp file.txt user@server:/home/user/

Copies local file to remote server

Example 2: Copy from Remote

scp user@server:/var/log/app.log ./

Downloads remote file to current directory

Example 3: Recursive Directory Copy

scp -r project/ user@server:/opt/

Copies entire directory structure

Authentication Methods

  1. Password authentication:

    scp file.txt user@server:/path/

  2. SSH key authentication:

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

  3. SSH agent:

    ssh-add ~/.ssh/id_rsa
scp file.txt user@server:/path/

Advanced Options

Option Description
-4 Force IPv4
-6 Force IPv6
-B Batch mode (no passwords/passphrases)
-F configfile SSH config file
-T Disable strict filename checking
-3 Copy between remote hosts via local

Common Usage Patterns

  1. Preserve attributes:

    scp -p file.txt user@server:/backup/

  2. Compressed transfer:

    scp -C largefile.tar user@server:/tmp/

  3. Custom SSH port:

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

Performance Optimization

  1. Enable compression for slow connections:

    scp -C file.txt user@server:/path/

  2. Limit bandwidth:

    scp -l 1000 file.txt user@server:/path/

  3. Use cipher optimization:

    scp -o Cipher=aes128-ctr file.txt user@server:/path/

Batch Operations

  1. Multiple files:

    scp file1.txt file2.txt user@server:/backup/

  2. Wildcard patterns:

    scp *.log user@server:/logs/

  3. From file list:

    cat filelist.txt | xargs -I {} scp {} user@server:/dest/

Security Considerations

  1. Use SSH keys instead of passwords
  2. Verify host keys
  3. Use specific SSH configurations
  4. Limit user permissions on target
  5. Monitor transfer logs

Additional Resources

Best Practices

  1. Use SSH keys for automation
  2. Test with small files first
  3. Verify transfers with checksums
  4. Use compression for large files
  5. Monitor network usage

SSH Configuration

Create ~/.ssh/config for easier usage:

Host myserver
    HostName server.example.com
    User myuser
    Port 2222
    IdentityFile ~/.ssh/mykey

Then use:

scp file.txt myserver:/path/

Error Handling

  1. Connection refused:

    scp -v file.txt user@server:/path/  # Debug mode

  2. Permission denied:

    scp -o PreferredAuthentications=publickey file.txt user@server:/path/

  3. Host key verification:

    scp -o StrictHostKeyChecking=no file.txt user@server:/path/

Scripting Examples

  1. Automated backup:

    #!/bin/bash
DATE=$(date +%Y%m%d)
scp -r /important/data/ backup@server:/backups/$DATE/

  2. Log collection:

    for host in server1 server2 server3; do
    scp $host:/var/log/app.log logs/$host-app.log
done

  3. Deployment script:

    scp -r dist/ production@server:/var/www/html/

Progress Monitoring

  1. Verbose output:

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

  2. With progress (using pv):

    pv file.txt | ssh user@server 'cat > /path/file.txt'

  3. Using rsync for progress:

    rsync --progress -e ssh file.txt user@server:/path/

Troubleshooting

  1. Connection timeouts
  2. Authentication failures
  3. Permission issues
  4. Network interruptions
  5. Disk space problems

Integration Examples

  1. With find:

    find . -name "*.conf" -exec scp {} user@server:/configs/ \;

  2. With tar:

    tar czf - directory/ | ssh user@server 'tar xzf - -C /destination/'

  3. Backup script:

    scp -r /home/user/ backup@server:/backups/$(date +%Y%m%d)/