To read files from PNFS using standard UNIX commands directly the system needs to over ride the normal POSIX interface. PRELOADING is the name given to this process in the UNIX operating system. To over ride the system. the environment variable LD_PRELOAD must be set.

export LD_PRELOAD=/opt/d-cache/dcap/lib/libpdcap.so 

This instructs library linking to link libpdcap.so in preference to the system libraries and so make allow unmodified UNIX applications can read from PNFS. The following example shows "cat" operating on a file stored in PNFS.

export LD_PRELOAD=/opt/d-cache/dcap/lib/libpdcap.so 
cat /pnfs/gridpp.rl.ac.uk/data/dteam/test1 
export LD_PRELOAD=""

GSI DCAP a client POSIX interposition library uses the same configuration but with an additional environment variable to be set indicating how to authenticate and transfer the requests over the network.