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Secure File Transfer (scp & rsync) ​

When you’re working with remote servers or cloud machines, you’ll often need to move files back and forth — maybe uploading your simulation code or downloading results. Two simple and reliable ways to do this are scp and rsync.

Both use SSH under the hood, so they’re secure and work seamlessly once your SSH connection is set up.

Let’s look at how to use them in a practical, easy-to-understand way.

Using scp (Secure Copy) ​

scp is the simpler of the two — think of it as “copy-paste over SSH.” It lets you copy files between your local system and a remote server safely.

Upload a file from local to remote ​

bash
scp myscript.py username@server_ip:/home/username/

This copies myscript.py from your computer to the remote server.

Download a file from remote to local ​

bash
scp username@server_ip:/home/username/output.txt ~/Downloads/

This downloads output.txt from the server into your local Downloads folder.

Copy entire folders ​

Add the -r flag (for recursive copy):

bash
scp -r results/ username@server_ip:/home/username/

That will copy your entire results folder to the server.

Tip: You can use either IP address or hostname (if you’ve set up an SSH config alias like myserver).

Using rsync (for smarter transfers) ​

rsync works like scp, but it’s smarter — it only copies what’s new or changed. So if you’re transferring large folders (like simulation outputs or datasets), rsync saves time and bandwidth.

Basic upload example ​

bash
rsync -avz myproject/ username@server_ip:/home/username/myproject/

Basic download example ​

bash
rsync -avz username@server_ip:/home/username/results/ ./results/

Here’s what the flags mean:

  • -a → preserves folder structure and permissions
  • -v → verbose (shows progress)
  • -z → compresses data during transfer (faster)

Pro Tip: You can add --progress to see live transfer updates:

bash
rsync -avz --progress ./data/ username@server_ip:/home/username/

Practical Example ​

Imagine you’ve finished a simulation on your cloud server and want to bring the results back:

bash
rsync -avz username@server_ip:/home/username/post-processing/output/ ./local_output/

This will copy everything inside the remote output/ folder to a local folder called local_output, only transferring new or changed files if you rerun it later.

Notes ​

  • Both scp and rsync use SSH, so they’re already secure — no need for passwords if you’ve set up SSH keys.

  • Use rsync for big or repeated transfers — it’s faster and smarter.

  • Always double-check the paths before running — especially if using -r (it can overwrite things).

  • If your remote port isn’t the default (22), you can specify it:

    bash
    scp -P 2222 file.txt user@server_ip:/home/user/
rsync -avz -e "ssh -p 2222" folder/ user@server_ip:/home/user/

  • To pause and resume large transfers, rsync can pick up exactly where it left off — scp cannot.

Summary ​

  • scp is perfect for quick, one-time file transfers between your local machine and a remote server.
  • rsync is ideal for large directories or repeated transfers, as it only copies what’s new or changed.
  • Both tools run securely over SSH, so there’s no extra setup once your SSH keys are ready.

With these two simple commands, you can move data between your laptop and remote servers effortlessly — no external tools, no fuss, just fast and reliable transfers.