The Network Data Server protocol, developed by the LIGO Scientific Collaboration, offers methods to remotely fetch data stored on disk, allowing users to download data to their laptops, or other machines.
The LIGO Data Grid operates the following NDS servers, with authenticated access for collaboration members:
| nds.ligo.caltech.edu | General access to the majority of available data |
| nds.ligo-la.caltech.edu | Lower-latency access to data from the LIGO Livingston Observatory |
| nds.ligo-wa.caltech.edu | Lower-latency access to data from the LIGO Hanford Observatory |
Warning
Fetching data via NDS requires the nds2-client package (including SWIG bindings for Python) to be installed on your system.
Data for a given Channel can be fetched from NDS using the TimeSeries.fetch() method:
>>> from gwpy.timeseries import TimeSeries
>>> data = TimeSeries.fetch('L1:PSL-ODC_CHANNEL_OUT_DQ', 1067042880, 1067042912)
where the arguments are a channel name, and GPS start and end times. Optionally, the NDS server to use can be specified using the host and port keyword arguments; if these are not given, GWpy will cycle through a logically-ordered list of hosts, starting the from host server for the relevant observatory.
Access to the authenticated NDS2 protocol services (all apart from nds40) require a valid and active kerberos ticket. On all Unix-based operating systems, the kinit command-line tool provided by the KRB5 package is the standard method of generating or renewing such a ticket. If this utility is available on your system, the TimeSeries.fetch() method will call it if connecting to the NDS server fails due to an authentication error, as in the following example:
>>> from gwpy.timeseries import TimeSeries
>>> data = TimeSeries.fetch('L1:PSL-ODC_CHANNEL_OUT_DQ', 1067042880, 1067042912)
error detail: SASL(-1): generic failure: GSSAPI Error: Unspecified GSS failure. Minor code may provide more information (Credentials cache file '/tmp/krb5cc_5308' not found)
Error authenticating against nds.ligo-la.caltech.edu
Please provide username for the LIGO.ORG kerberos realm: albert.einstein
Password for albert.einstein@LIGO.ORG:
Kerberos ticket generated for albert.einstein@LIGO.ORG
where the user has been prompted for both their LIGO.ORG username and password, in order to generate a ticket.
Users can generate a kerberos keytab file to enable password-less tickets using the ktutil tool:
Run ktutil:
$ ktutil
At the ktutil: prompt enter:
addent -password -p albert.einstein@LIGO.ORG -k 1 -e des3-cbc-sha1
and enter your password when prompted. At the next prompt enter wkt followed by the name of the kerberos keytab to write to, and then quit:
wkt albert.einstein.keytab
quit
Users should store the location of this file in the KRB5_KTNAME environment variable, enabling TimeSeries.fetch() to locate and utilise the keytab for seamless authentication.