Data Transfer Tool: GridFTP (certificate-based authentication)

This article describes how to transfer data using gridftp with certificate- based authentication.

Basics of certificate-based authentication  

Gridftp servers commonly use a network of “trust” based on electronic certificates. In order to make use of a gridftp server at one end of your proposed transfer, you will need to use a certificate which identifies you as the user, and which is issued by an identity provider which is “trusted” by the servers at both ends. The trust between the servers is maintained by the administrators of the service who will ensure that the necessary certificates are in place.

The presentation of a valid credential which is trusted by the server at the other end is merely the authentication step (proving who you are). Authorisation also needs to follow: you, as a user (identified by the credential you present) need to be authorised to use the resource at the other end. You should check with the operator of the other gridftp server to see what additional steps are required before you can actually perform a transfer.

Getting a short-term credential  

In order to access the JASMIN gridftp server, you can now use your JASMIN portal account to gain a short-term credential which the server will recognise to authenticate you. This is the same username and password you would use to log in to https://accounts.jasmin.ac.uk  to administer your JASMIN account. IT IS NOT YOUR SSH PASSPHRASE.

Here’s what to do:

1. Download tools to interact with JASMIN’s Online Certificate Authority (OnlineCA). You can use these to interact with other OnlineCAs too (not just JASMIN’s. These replace the “myproxy-logon” tool previously mentioned here)
2. Use these tools to: 1. “Bootstrap trust” i.e. to setup your local certificate store with those needed to interact with the JASMIN server [First time use only] 2. Obtain a short-term credential using your JASMIN account details [First time, and to renew your short-term credendial as needed]
3. Use this short-term credential to authenticate with a remote gridftp server which trusts this credential (for example, the JASMIN gridftp server)

Download OnlineCA tools  

On the machine you intend to use as the transfer client, e.g. xfer1.jasmin.ac.uk, in your JASMIN home directory, download 2 shell scripts which will interact with the Online CA for you. Make them executable:

wget https://raw.githubusercontent.com/cedadev/online_ca_client/master/contrail/security/onlineca/client/sh/onlineca-get-cert-wget.sh
wget https://raw.githubusercontent.com/cedadev/online_ca_client/master/contrail/security/onlineca/client/sh/onlineca-get-trustroots-wget.sh
chmod u+x onlineca-get-*.sh

View help information for the shell scripts:

./onlineca-get-trustroots-wget.sh -h
./onlineca-get-cert-wget.sh -h

Bootstrap trust between your own machine and the JASMIN gridftp server: (First time only)

./onlineca-get-trustroots-wget.sh -U https://slcs.jasmin.ac.uk/trustroots/ -b
Bootstrapping Short-Lived Credential Service root of trust.
Trust roots have been installed in /home/users/USERNAME/.globus/certificates.

Obtain a credential, to be written to an output file credfile using your JASMIN Accounts Portal username USERNAME:

./onlineca-get-cert-wget.sh -U https://slcs.jasmin.ac.uk/certificate/ -l USERNAME -o ./cred.jasmin

When prompted, enter the password associated with your JASMIN account (NOT your SSH passphrase)

Change the permissions on your newly-created cred.jasmin file so that it’s only readable by you (client software may insist on this):

chmod 600 ./cred.jasmin

This credential obtained by this method is valid by default for 720 hours (30 days), as you can see by inspecting the certificate using the following command:

openssl x509 -in cred.jasmin -noout -startdate -enddate
    notBefore=Mar 11 17:32:59 2022 GMT
    notAfter=Apr 10 17:32:59 2022 GMT

After the notAfter date, it will no longer be valid, but you can repeat this process at any time (e.g. before it expires) to update it.

Example Gridftp usage  

(General case, or with a JASMIN host as gridftp client)

Once you have obtained a valid short-term credential on the client transfer server, and assuming that the gridftp server at the remote end of the transfer recognises and is able to authorize you via this credential, then you should be able to transfer data between the remote server and local client with commands such as shown below:

Please consult the documentation for the globus-url-copy command for the full range of options and arguments.

Please note that the examples below use a fictitious client gridftp-client.localsite.ac.uk and server gridftp-server.remotesite.ac.uk which need to be replaced in your commands with the hostname of the actual gridftp server and client you are actually using.

Check help documentation for the globus-url-copy command:

globus-url-copy -help

NOTE: On some systems, you have to load a relevant module to get access to the globus-url-copy command, however not on the JASMIN [hp]xfer servers.

It is recommended to try things out using the regular xfer servers xfer-vm-0[12] but to perform “real” transfers using hpxfer[34] for better performance.

1. Remote directory listing issued by client on gridftp- client.localsite.ac.uk to server gridftp-server.remotesite.ac.uk where you have a home directory /home/users/USERNAME:

globus-url-copy -cred cred.jasmin -vb -list gsiftp://gridftp-server.remotesite.ac.uk/home/users/USERNAME/

2. Download a file from remote directory /home/users/USERNAME to destination on the client machine:

globus-url-copy -cred cred.jasmin -vb gsiftp://gridftp-server.remotesite.ac.uk/home/users/USERNAME/myfile file:///path/to/localdir/myfile

The -p N and -fast options can additionally be used in combination to enable N parallel streams at once, as shown below. You can experiment with N in the range 4 to 16 to obtain the best performance, but please be aware that many parallel transfers can draw heavily on shared resources and degrade performance for other users:

globus-url-copy -cred cred.jasmin -vb -p 16 -fast gsiftp://gridftp-server.remotesite.ac.uk/home/users/USERNAME/myfile file:///path/to/localdir/myfile

3. Recursively download the contents of a directory on a remote location to a local destination.

globus-url-copy -cred cred.jasmin -vb -p 4 -fast -cc 4 -cd -r gsiftp://gridftp-server.remotesite.ac.uk/home/users/USERNAME/mydir/ file:///path/to/localdir/mydir/

Where:

• -cc N requests N concurrent transfers (in this case, each with p=4 parallel streams)
• -cd requests creation of the destination directory if this does not already exist
• -r denotes recursive transfer of directories

• -sync and -sync-level options can be used to synchronise data between the two locations, where destination files do not exist or differ - y criteria that can be selected) from corresponding source files. See -help option for details.

• the file:/// URI is used to specify the destination on the local file system.

Uploading data  

The above commands can also be adapted to invoke transfers from a local source to a remote destination, i.e. uploading data, since the commands all take the following general form:

globus-url-copy [OPTIONS] source-uri desination-uri

You can use the above examples by replacing the local machine gridftp-client.localsite.ac.uk with one of the jasmin xfer or hpxfer servers as a client, To do this, you first need to be logged in via SSH to one of these hosts and can initiate a transfer by invoking globus-url-copy in one of the ways above.

• For high-performance transfer (large volumes and/or longer distances), use Globus or the hpxfer servers
• For remote hosts using JASMIN’s dedicated network link (Met Office only) use xfer-vm-0[123].jasmin.ac.uk as the client (These are virtual machines so have limited performance, but your transfer will be over a dedicated network connection)

Connecting to the JASMIN GridFTP server  

In order to do a transfer using a JASMIN host as the gridftp server (rather than client), you would need to interact with the JASMIN GridFTP server gridftp1.jasmin.ac.uk. You cannot log in to this server directly via SSH: you only initiate GridFTP transfers to and from it from another client.

In the following example, a client is initiated on a fictitious remote host client.remotesite.ac.uk and tests the connection by transferring from /dev/zero on the local machine (at remotesite ) to /dev/null on the JASMIN gridftp server. Note that you can use the SLCS server at JASMIN to obtain the short-term credential required ( but the first time, you will need to download and use the OnlineCA tools as described above ). You can renew your credential and perform the test transfer as follows:

./onlineca-get-cert-wget.sh -U https://slcs.jasmin.ac.uk/certificate/ -l USERNAME -o ./cred.jasmin
globus-url-copy -cred cred.jasmin -vb -p 8 -fast /dev/zero gsiftp://gridftp1.jasmin.ac.uk/dev/null
    Source: file:///dev/
    Dest:   gsiftp://gridftp1.jasmin.ac.uk/dev/
      zero  ->  null

    4153409536 bytes       792.20 MB/sec avg       792.20 MB/sec inst

This server is also used as the JASMIN GridFTP Server globus endpoint, see GridFTP transfers using Globus Online (however you can only currently use your CEDA SLCSs credential with Globus Online. The JASMIN team is working on a solution for this).

Please note that the servers xfer-vm-0[123].jasmin.ac.uk and hpxfer[34].ceda.ac.uk are not gridftp servers. They have the globus-url-copy client installed, so can be used as clients to connect to remote gridftp servers, and also support gridftp over SSH (both incoming and outgoing), but do not act as servers for certificate-based gridftp as shown in these examples. The JASMIN gridftp server for read-write access to home directories and group workspaces is gridftp1.jasmin.ac.uk. Access to this requires the hpxfer access role. See also Transfer Servers.

Third-party transfers  

It should be possible, with the correct configuration at each site, to initiate on host A a transfer of data between two other gridftp servers B and C (a third party transfer). Both URIs would use gsiftp: as the protocol:

globus-url-copy -vb -p 4 gsiftp://B/source gsiftp://C/destination

Further information can be found in the documentation for globus-url-copy.

This is the basis of the Globus Online  managed service to orchestrate and monitor transfers between gridftp endpoints in a more user-friendly way. It has evolved considerably since diverging from the “traditional” gridftp setup described in this article and is recommended as it provides a much easier user experience and better reliability.

See Globus transfers with JASMIN.

Future plans  

As [support for the open-source Globus Toolkit (including globus-url-copy) has now been withdrawn by Globus]( https://www.globus.org/blog/support-open-source-  globus-toolkit-ends-january-2018), the future of direct gridftp transfers is uncertain. It is currently maintained by the Grid Community Forum.

We advise users to spend some time understanding and testing transfer workflows with the Globus Online transfer service, including the command-Line, web interfaces and (for advanced users) a Python SDK, as these are likely to replace direct gridftp on JASMIN in due course.