How to transfer files between two Linux computers

7. September 2020
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It is pretty usual that when you want to run your Machine Learning project, you need to download or transfer the dataset form somewhere to your local machine or any machine you want to run your project.

So, it would be very important to learn how we can copy a big dataset from another computer to our local computer on Linux.

One of the simplest ways to transfer files on Linux is using the "SCP" command. So, let's get more into it:

SCP, Secure Copy Linux Command

SCP (secure copy) is a command-line utility that allows you to securely copy files and directories between two locations. SCP copies files between hosts on a network. It uses ssh for data transfer, and uses the same authentication and provides the same security as ssh.

With SCP, you can copy a file or directory:

  • From your local system to a remote system.
  • From a remote system to your local system.
  • Between two remote systems from your local system.

When transferring data with SCP, both the files and password are encrypted that's why we call it secure copy command.

SCP Command Syntax

The following form is the basic synatx of using SCP.

scp [OPTION] [user@]SRC_HOST:]file1 [user@]DEST_HOST:]file2
  • Option: it includes cipher, ssh configuration, ssh port, limit, recursive copy and so on.
  • [user@]SRC_HOST:]file1: it contains the address of the host files.
  • [user@]DEST_HOST:]file2: the location of the destination file or directory should mention here.
  • The colon (:): to distinguish between SSH or IP address and the location of files.

Sometimes the address of host files is not as simple and clear as we expect so, in this case, using "tree" command can be SO helpful to find the location of data you need to work on it for your project.

When copying a source file to a target file which already exists, scp will replace the contents of the target files.

If the target file does not yet exist, an empty file with the target file name is created, then filled with the source file contents. No attempt is made at "near-atomic" transfer using temporary files.

SCP Options

There are some options to help us to use the SCP command effectively.

Let’s review some parameters of SCP command.

  • -P(Capital P) - Specifies the remote host ssh port.
  • -p - Preserves files modification and access times, and modes from the original files.
  • -q - Use this option if you want to suppress the progress meter and non-error messages.
  • -C - This option forces the SCP to compresses the data as it is sent to the destination machine.
  • -r - This option allows the SCP to copy all files and directories of the host address.

Example of using SCP

  1. Copy file from a Linux server to a local computer or vice versa.

    scp username@remote:/file/to/send /where/to/put/local-machine

  2. Copy file between two remote hosts.

    scp username@remote_1:/file/to/send username@remote_2:/where/to/put

  3. Using -r option to copy all file and directory of the host address.

    scp -r username@remote_host:/file/to/send username@remote_des:/where

Sometimes, the files you want to copy from the host are not at the same folder or directory, so we need to repeat SCP command for different locations, instead of repeating the SCP command we can make a bash file containing the several SCP commands for the different host address.

SCP and authentication

The SCP command works on ssh to transfer data, so it requires an ssh key or password to authenticate on the remote systems.

For transferring files, it reads permissions on the source file and copies permission on the target machine.

It is interesting to know that SCP will overwrite files (if the name of files for the host and destination was the same) without any warning.

You may also want to set up an SSH key-based authentication and connect to your Linux servers without entering a password. Please review this post to learn a method to get rid of typing your passwords while multiple SCP commands are running.

Conclusion

In this post, you learned how to use the SCP Linux command to copy files and directories from the host machine to destination machine. we revied some important parameters of the SCP command to make using it more effectively.

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