The lcg_util RPM
contains many small command line applications which interact
with SRM implementations, these where developed
independently from dCache and provided by the
LCG grid computing effort.
Each command line application operates on a different method
of the SRM interface. These applications where not designed
for normal use but to provide components upon which operations
can be built.
lcg-gt queries the BDII information server. This adds an additional requirement that the BDII information server can be found by lcg-gt, please only attempt to contact servers found on your user interface using.
[user] $lcg-infosites --vo dteam se
SRM provides a protocol negotiating interface, and returns
a TURL (transfer URL). The protocol specified by the
client will be returned by the server if the server supports
the requested protocol.
To read a file from dCache using lcg-gt
you must specify two parameters the SURL (storage URL),
and the protcol (GSIdCap or GSI-FTP) you wish to use to
access the file.
[user] $lcg-gt srm://srm-door.example.org/pnfs/example.org/data/dteam/group gsidcapgsidcap://gsidcap-door.example.org:22128/pnfs/example.org/data/dteam/group -2147365977 -2147365976
Each of the above three lines contains different information. These are explained below.
gsidcap://gsidcap-door.example.org:22128/pnfs/example.org/data/dteam/group
is the transfer URL (TURL).
-2147365977 is the SRM Request
Id, Please note that it is a negative number in
this example, which is allowed by the specification.
-2147365976 is the Unique identifier for
the file with respect to the Request
Id. Please note that with this example this is a
negative number.
Request Id
dCache limits the number of Request
Ids a user may have. All Request
Ids should be returned to dCache using the
command lcg-sd.
If you use lcg-gt to request a file with
a protocol that is not supported by dCache the command
will block for some time as dCache’s SRM interface times
out after approximately 10 minutes.
This command should be used to return any TURLs given by
dCache’s SRM interface. This is because dCache
provides a limited number of TURLs available concurrently.
lcg-sd takes four parameters: the SURL,
the Request Id, the File
Id with respect to the Request
Id, and the direction of data transfer.
The following example is to complete the get operation, the values are taken form the above example of lcg-gt.
[user] $lcg-sd srm://srm-door.example.org:22128/pnfs/example.org/data/dteam/group " -2147365977" " -2147365976" 0
dCache returns negative numbers for Request
Id and File Id. Please note
that lcg-sd requires that these values
are places in double-quotes with a single space before the
- sign.
The Request Id is one of the values
returned by the lcg-gt command. In this
example, the value (-2147365977) comes
from the above example lcg-gt.
The File Id is also one of the values
returned returned by the lcg-gt command.
In this example, the value (-2147365976)
comes from the above example lcg-gt.
The direction parameter indicates in which direction data
was transferred: 0 for reading data and
1 for writing data.