Copying files using scp

SSH keys are required to connect to Puhti and Mahti over SSH

Since April 14th 2025, connecting to Puhti and Mahti over SSH only works using SSH keys added in MyCSC. Password authentication and public keys stored in users' personal ~/.ssh/authorized_keys file on the supercomputer no longer works.

Read the detailed instructions on setting up and using SSH keys.

Copying files between different Linux, macOS and Windows machines can be done with the scp command. Thus, you can use scp to transport data between CSC and your local computer, or between different file systems at CSC.

The basic syntax for copying data from a local machine to a remote server is:

scp /path/to/file username@server:/path/to/remote/destination

And correspondingly the syntax to copy files from a remote server to a local machine is:

scp username@server:/path/to/file /path/to/local/destination

Non-standard location or name for SSH keys

If you have stored your SSH key file with a non-default name or in a non-default location (somewhere else than ~/.ssh/id_<algorithm>), you must specify where scp should look for the key using the -i option, e.g:

scp -i /path/to/sshkey /path/to/file username@server:/path/to/remote/destination

The rest of this page assumes the key is stored in a default location using a standard name, so the -i flag is omitted.

Using scp to copy data between your local computer and Puhti

For example, the command to copy a local file data.txt from the current directory to the home directory of user bob on Puhti would be:

scp data.txt bob@puhti.csc.fi:~/

The special symbol ~ points to the user's home directory. You can use the csc-workspaces command on Puhti to show other available disk areas.

To copy complete directories, you should use scp command with option -r. For example:

scp -r /path/to/data_directory bob@puhti.csc.fi:/scratch/project_2001234/data_dir

The above command would copy the directory data_directory and all its contents to Puhti at /scratch/project_2001234/data_dir.

Copying the data from a CSC server to your local machine is done in the same way:

scp bob@puhti.csc.fi:/scratch/project_2001234/data.txt .

The . symbol points to the current working directory on your local machine, i.e. the location where you're running the scp command.

In the commands above, files and directories have been copied one at a time. However, scp can also copy several files at once. For example:

scp data1.txt data2.txt data3.txt bob@puhti.csc.fi:~/

You can also use wildcards when defining the files to be copied. For example, to copy all files with extension .txt from the current directory on your local machine to your home directory on Puhti, you could use the command:

scp *.txt bob@puhti.csc.fi:~/

By default, the copied files are treated as new files, but if you add option -p to the scp command, then the copied file will inherit the timestamp and access mode information from the original file.

Using scp to copy data directly between CSC supercomputers

To copy data directly between CSC supercomputers, scp must be able to access the SSH keys you've set up on your local workstation for authenticating to CSC supercomputers. This is accomplished by forwarding your SSH agent to the supercomputer you're first connecting to.

After this, scp can be used to copy data directly between CSC supercomputers using the same syntax as above. For example, the command to copy a file data.txt from directory /scratch/project_2001234 on Puhti to the same directory on Mahti would be:

scp /scratch/project_2001234/data.txt bob@mahti.csc.fi:/scratch/project_2001234