SCP

In short: Secure Copy Protocol — a simple command-line tool and protocol for copying files between computers over an encrypted SSH connection.

In more detail: Syntactically modelled on cp (scp file.txt user@host:/path/), but network-capable. Now considered outdated compared with SFTP (more functions, better error handling), but because of its simplicity still widely used for quick one-off copies.

In Depth

A typical SCP command:

# Copy a file to the server
scp local-file.txt user@server.example.com:/path/target/
 
# Fetch a file from the server
scp user@server.example.com:/path/file.txt ./local/
 
# Copy a whole folder recursively
scp -r local-folder/ user@server.example.com:/path/

For the transfer, SCP uses the same encrypted connection as a normal SSH session — so there’s no separate login step; authentication runs identically to an ordinary SSH login (password or key pair). The big criticism of the SCP protocol: it offers hardly any way to resume interrupted transfers, and its error messages are often not very meaningful — exactly the points that SFTP, as a more modern successor, solves much better. Many SSH implementations have now even deactivated SCP support by default and explicitly recommend SFTP.

See also: SFTP, SSH