Accessing Swestore with the ARC client

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The ARC client

This guide describes how to use the Nordugrid ARC client for storing and retrieving files from SweStore National Storage. The ARC client is usually used for sending grid jobs to grid clusters, but it also contain commands for data management.

If your system doesn't have the ARC client installed you can look at the ARC client installation page in this wiki or the official Nordugrid [http://www.nordugrid.org/documents/arc-client-install.html ARC installation] page for more information. Please note that the windows and MacOS clients are a bit unstable.

A complete user guide for the ARC client can be found in http://www.nordugrid.org/documents/arc-ui.pdf.

ARC can handle many different file transfer protocols, such as: http, https, httpg, ftp, gsiftp, lfc, rls, srm. But only the srm protocol is currently is supported when accessing SweStore using the ARC client.

ARC 0.8 versus 1.0

In late spring 2011 Nordugrid release the 1.0 version of ARC (sometimes called 11.05). One of the new features of 1.0 compared to the previous 0.8 release was a new command set. Basically most of the ng* commands was replaced with the new arc* commands. Some functionality moved between commands (ngstat became arcinfo and arcstat) and some new commands was introduced (arcproxy as an replacement for grid-proxy-init, which wasn't an arc command at all but a part of the Globus Toolkit). There are still legacy compatibility binaries in place for the old ng* commands, but I strongly suggest that you use arc* when available.

If you on the same local account switch between ng* and arc* commands you may get warnings:

Bad format detected in file /home/jens/.arc/srms.conf, in line srm.swegrid.se 8443 2.2
Unwrapped data does not fit into buffer
Connection to server failed: Connection refused
Connection to server failed: Connection refused

or

WARNING: Bad or old format detected in file /home/jens/.arc/srms.conf, in line srm.swegrid.se 8443 gsi 2.2
WARNING: Bad or old format detected in file /home/jens/.arc/srms.conf, in line srm.swegrid.se 8443 gsi 2.2

There is a file, srm.conf, that gets automatically updated when accessing a resource. ngls and arcls does not agree on the content of that file. There are bug reports about it. That warning is just confusing and shouldn't be displayed. Another attempt using the same command will probably not display those errors again.

arcproxy 1.0.1

There us a bug in dCache which makes proxy certificates from arcproxy 1.0.1 unusable. The error you get is:

ERROR: Failed listing files

All other version of arcproxy should be fine. If you encounter this version av arcproxy, please use grid-proxy-init if available. The generated proxy certificates should be equivalent.

Preparations

In addition to the installed ARC client you need the proper access rights and a valid grid proxy certificate. Please check the Grid certificates page for more information.

Copying files

Copying files to and from resources is accomplished using the arccp command.

Copying single files

Copying single files is accomplished in the same way as using the normal cp command as shown in the following example:

$ arccp archive.tar.gz srm://srm.swegrid.se/ops/

Please note the trailing / which marks the destination as a directory. Without a / the destination will be a file, which may or may not be what you wanted. All required directories are created when needed so the destination may be a nonexisting directory.

Recursive copying

Recursive copying is accomplished using the --recursive option to arccp. The argument to the option determines the depth of the recursive copy.

$ arccp --recursive=3 foobar/ srm://srm.swegrid.se/ops/foobar/

Listing files

Listing files on a resources is done using the arcls command. In the simplest form the command just takes a URL as input and displays names and directories without any extra information as shown in the following example:

$ arcls srm://srm.swegrid.se/ops/
motd.1
bla
generated
ops
motd.f343

Additional information can be listed by adding the --long option:

$ arcls --long srm://srm.swegrid.se/ops
<Name> <Type> <Size> <Creation> <Validity> <CheckSum> <Latency>
motd.1 file 354 2008-06-05 12:28:23 (n/a) adler32:582d7718 NEARLINE
bla dir 512 2008-08-22 12:23:49 (n/a) (n/a) NEARLINE
foobar dir 512 2008-11-17 15:07:39 (n/a) (n/a) NEARLINE
ops dir 512 2010-01-21 11:26:00 (n/a) (n/a) NEARLINE
motd.f343 file 436 2010-01-08 14:35:40 (n/a) adler32:0fed94f2 ONLINE

Metadatainformation on a specific file can be listed by specifying the -m or --metadata option. In the following example the metadata information of the motd.1 file is shown:

$ arcls --metadata srm://srm.swegrid.se/ops/motd.1
/ops/motd.1
accessperm:rw-r--r--
checksum:adler32:582d7718
ctime:2008-06-05 12:28:23
filestoragetype:PERMANENT
group:25001
latency:NEARLINE
lifetimeassigned:PT1S
lifetimeleft:PT1S
mtime:2011-03-24 12:57:42
owner:25001
path:/ops/motd.1
size:354
spacetokens:
type:file

Creating directories

There is no command line tool for creating directories. This command will probably be added in an upcoming release. In the meantime the following procedure can be used:

$ touch dummyfile
$ arccp dummyfile srm://srm.swegrid.se/ops/newdir/
$ arcls srm://srm.swegrid.se/ops/newdir/
dummyfile

The dummmyfile can be removed using the arcrm command described in the following section.

Removing files or directories

$ arcrm srm://srm.swegrid.se/ops/newdir/dummyfile
$ arcrm srm://srm.swegrid.se/ops/newdir/

To remove directories they have to be empty.