Complete Guide to the SCP Command: Secure File and Directory Copy

SCP Command Format and Basic Usage

The SCP (Secure Copy Protocol) command is used to securely copy files and directories between a local host and a remote host, or between two remote hosts, using the SSH protocol. Its basic command format is:

scp [options] [source_path] [destination_path]

Copy a File from Local to Remote Host

Copy the local file /home/abc.tar.gz to the /root/ directory on remote host 123.123.123.123, using a non-default SSH port 2233:

scp -P 2233 /home/abc.tar.gz [email protected]:/root/abc.tar.gz

Explanation:

• -P 2233: Specifies the SSH port number as 2233. This parameter can be omitted if the remote host uses the default port 22.
• [email protected]:/root/abc.tar.gz: Specifies the remote destination. The format is username@host:path.

Copy a File from Remote Host to Local

Copy the file test.tar.gz from the /remote/ directory on remote host 10.23.185.16 to the local /local/ directory, preserving the file's original attributes (modification time, access time, permissions), and optionally rename it:

scp -P 2223 -p [email protected]:/remote/test.tar.gz /local/test.tar.gz

Explanation:

• -p: Preserves the source file's modification time, access time, and access permissions.
• -P 2223: Specifies the SSH port (note the uppercase P).
• The destination path /local/test.tar.gz can be customized, allowing you to rename the file during the copy.

Common SCP Command Options Explained

Below are common SCP command options and their descriptions:

• -1: Forces the use of SSH1 protocol (obsolete; SSH2 is recommended).
• -2: Forces the use of SSH2 protocol (default for modern systems).
• -4: Forces the use of IPv4 addresses only.
• -6: Forces the use of IPv6 addresses only.
• -B: Uses batch mode; does not prompt for passwords or passphrases during transfer.
• -C: Enables compression; passes the -C flag to SSH to improve efficiency for large file transfers.
• -p: Preserves the source file's modification time, access time, and access permissions.
• -q: Quiet mode; suppresses the transfer progress meter.
• -r: Recursively copies entire directories and their contents.
• -v: Verbose mode; outputs debug messages about the entire transfer process, useful for troubleshooting connection or configuration issues.
• -c cipher: Specifies the encryption cipher (e.g., aes256-ctr); this option is passed directly to SSH.
• -F ssh_config: Specifies an alternative SSH configuration file path.
• -i identity_file: Specifies the path to the private key file for authentication (e.g., ~/.ssh/id_rsa).
• -l limit: Limits the bandwidth used for the transfer, in Kbit/s (e.g., -l 800 limits to 800 Kbit/s).
• -o ssh_option: Passes additional options in SSH configuration format (e.g., -o StrictHostKeyChecking=no).
• -P port: Note the uppercase P; specifies the SSH connection port number (default is 22).
• -S program: Specifies the path to the program used for the encrypted connection; this program must understand SSH options.

Usage Tips and Important Notes

1. Specifying Port: If the remote SSH service runs on a non-default port, you must use the -P parameter (uppercase) to specify it. The lowercase -p is for preserving file attributes. These have different functions; be careful not to confuse them.

2. Recursive Directory Copy: When copying a directory, you must use the -r option, for example:

scp -r /local/directory/ user@remote-host:/remote/path/

3. Using Key Authentication: For improved security and automation, it is recommended to configure SSH key pairs and specify the private key using the -i option:

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

4. Bandwidth Limiting: Use the -l option to limit transfer speed when bandwidth is constrained or to avoid impacting other services.

5. Special Characters in Paths: If file or directory names contain spaces or other special characters, enclose the paths in quotes, for example: scp "local file.txt" user@host:"/remote path/".