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CernVM File System on Personal Workstations

About CernVM File System

The CernVM File System ("CernVM-FS" or "CVMFS") is a tool that allows for efficient global distribution of software and data that does not change frequently. Its name indicates its origins for use by virtual machines in use by the high energy physics community, however, it has wider applicability and usage. It caches files to disk so that, after the initial download, file access for the client is speedy.

Within LIGO, CVMFS is being used to distribute both instrument data ("frame files") and analysis software for use at LIGO computing sites and on the Open Science Grid (OSG). You may elect to install CVMFS on your workstation for ease of access to recent data and software. The MacOS CVMFS client cannot yet access LIGO instrument data, though it is hoped that that feature will be developed. You should pay attention to the LIGO Software Container as it is developed to see if it may facilitate access to instrument data on your workstation.

Installation

Configuration

CVMFS uses a technology called FUSE to access remote data. On MacOS, it will be configured correctly automatically. On both Debian and Scientific Linux, you must make one configuration change to FUSE for CVMFS to work properly. Cut-and-paste these commands exactly!
sudo sed -i 's/#[[:space:]]*user_allow_other/user_allow_other/' /etc/fuse.conf
cat /etc/fuse.conf

The 2nd command should show that the option user_allow_other is present and not commented. If it is not, use your favorite editor to add it to the file.

The configuration that is installed by default is only appropriate for the low amount of traffic one might expect from a single client. After testing usage, please consider setting some Advanced Configuration Options for improved performance.

Usage

At this point, anyone can find LIGO software such as pyCBC and lalsuite under
ls -lh /cvmfs/oasis.opensciencegrid.org/ligo/sw

If you are a LIGO-Virgo member and you are running CVMFS on Linux, you should be able to able access recent LIGO instrument data with the following commands.
ligo-proxy-init albert.einstein
ls -lh /cvmfs/oasis.opensciencegrid.org/ligo/frames

Advanced Configuration Options

The full range of CVMFS options are discussed in its documentation. These options should be set in /etc/cvmfs/default.local. Two important options are set in this file upon installation. If you make any changes, you must subsequently run
sudo cvmfs_config reload

Local cache for fast access

CVMFS_QUOTA_LIMIT=20000

This tells your client to cache up to 20,000 MB of data on your workstation so that they are accessed at high speed. You can change it to any number you see fit.

Nearby cache for faster downloads

The default behavior of the client is to connect directly to "central" CVMFS servers that serve data from non-LIGO sites to LIGO computing sites. If you are at a LIGO computing site, it may be faster and cause less data usage for your internet connection to use a cache installed by your computing staff. If you configure a campus-based cache and take your laptop off-campus -- or are not actually at that campus! -- it will failover to a direct connection, although there may be a noticeable delay as it fails to connect to the campus-based cache. Recommended values for the CVMFS_HTTP_PROXY option are below.
Topic revision: r15 - 2018-07-03, thomas.downes@ligo.org
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