VOMS Clients guide

For VOMS clients 3.0.6

Table of contents

Installing the clients  

To install the VOMS clients, configure the UMD repositories as appropriate for your target distribution.

On SL/CENTOS 6, VOMS clients are installed with the following command:

yum install voms-clients3

On CENTOS 7, VOMS clients are available in EPEL 7, and are installed with the following command:

yum install voms-clients-java

Configuring VOMS trust anchors  

VOMS clients need local configuration to validate the signature on Attribute Certificates issued by trusted VOMS servers.

The VOMS clients and APIs look for trust information in the /etc/grid-security/vomsdir directory.

The vomsdir directory contains a directory for each trusted VO. Inside each VO directory two types of files can be found:

  • An LSC file contains a description of the certificate chain of the certificate used by a VOMS server to sign VOMS attributes.
  • An X509 certificates used by a VOMS server to sign attributes.

These files are commonly named using the following pattern:


where hostname is the host where the VOMS server is running.

When both lsc and pem files are present for a given VO and hostname, the lsc file takes precedence.

The LSC file contains a list of X.509 subject strings, one on each line, encoded in OpenSSL slash-separated syntax, describing the certificate chain (up and including the CA that issued the certificate). For instance, the voms.cnaf.infn.it VOMS server has the following LSC file:


For more details see the vomsdir man page.

Configuring VOMS server endpoints  

The list of known VOMS server is maintained in vomses files. A vomses file is a simple text file which contains one or more lines formatted as follows:

"vo_name" "hostname" "port" "dn" "alias"

where vo_name is the name of the VO served by the VOMS server, hostname is the hostname where the VOMS server is running, port is the port where the VOMS server is listening for incoming requests, dn is the subject of the certificate of the VOMS server, and alias is an alias that can be used for this VOMS server (this is typically identical to the vo_name).

System wide VOMSES configuration is maintained in the /etc/vomses file or directory. If /etc/vomses is a directory, all the files contained in such directory are parsed looking for VOMS contact information.

A user can define its custom vomses configuration in the ~/.glite/vomses file or directory, which will be parsed in the same way as just described.

For more details on how to configure vomses files on the system, see the vomses man page.

User credentials  

While user credentials may be put anywhere, and then their location passed to voms-proxy-init via the appropriate options, there are obviously default values.

User credentials should be put in the $HOME/.globus directory.

Certificates encoded in PKCS12 and PEM formats are correctly handled by the VOMS clients.

The default path for looking up PKCS12 credentials is:


Permissions on $HOME/.globus/usercred.p12 must be 600.

For PEM credentials the following paths are used:

$HOME/.globus/usercert.pem (certificate)
$HOME/.globus/userkey.pem (private key)

Permissions on the pem files must be:

  • 644 for $HOME/.globus/usercert.pem
  • 400 for $HOME/.globus/userkey.pem

In case both the PEM and PKCS12 formats are present, PEM takes precedence.

Controlling java options

To the change the options with which the virtual machine that executes the clients is started, use the VOMS_CLIENTS_JAVA_OPTIONS environment variable. For example, for setting the maximum heap size to 2MB, use


Creating a proxy  

The command voms-proxy-init is used to contact the VOMS server and retrieve an AC containing user attributes that will be included in the proxy certificates.

$ voms-proxy-init --voms voname

where voname is the name of the VO to which the user belongs. This will create a proxy containing all the groups to which the user belongs. The -voms option may be specified multiple times in case the user belongs to more than one VO.

Omitting the –voms option results in the creation of a plain proxy, as you would get running grid-proxy-init.

No roles are ever include in proxy by default. In case they are needed, they must be explicitly requested. For example, to request the role sgm in the /test/italian group, the following syntax should be used:

$ voms-proxy-init --voms test:/test/italian/Role=sgm

thus obtaining a role that will be included in the AC, in addition to all the other information that will be normally present. In case multiple roles are needed, the -voms option may be used several times.

By default, all FQANs explicitly requested on the command line will be present in the returned credentials, if they were granted, and in the exact order specified, with all other FQANs following in an unspecified ordering. If a specific order is needed, it should be explicitly requested via the -order option. For example, the following command line:

$ voms-proxy-init --voms test:/test/Role=sgm --order /test

asks for the Role sgm in the root group, and specifies that the resulting AC should begin with membership in the root group instead, while posing no requirements on the ordering of the remaining FQANs. This also means that with the above command line there is no guarantee that the role will end up as the second FQAN. If this is desired, use the following command line instead:

$ voms-proxy-init --voms test:/test/Role=sgm --order /test --order /test/Role=sgm

The validity of an AC created by VOMS will generally be as long as the proxy which contains it. However, this cannot always be true. For starters, the VOMS server is configured with a maximum validity for all the ACs it will create, and a request to exceed it will simply be ignored. If this happens, the output of voms-proxy-init will indicate the fact.

For example, in the following output (slightly reformatted for a shorter line then on screen):

$ voms-proxy-init --voms valerio --vomslife 50:15
Enter GRID pass phrase:
Your identity: /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini
Creating temporary proxy .................................... Done
Contacting datatag6.cnaf.infn.it:50002
[/C=IT/O=INFN/OU=Host/L=CNAF/CN=datatag6.cnaf.infn.it] "valerio" Done
Warning: datatag6.cnaf.infn.it:50002:
The validity of this VOMS AC in your proxy is shortened to 86400 seconds!
Creating proxy ......................................... Done
Your proxy is valid until Fri Sep 8 01:55:34 2006

You can see that the life of the voms AC has been clearly shortened to 24 hours, even though 50 hours and 15 minutes had been requested.

If your certificate is not in the default place, you may specify it explicitly by using the –cert and –key options, like in the following example:

voms-proxy-init --voms valerio --cert \$HOME/cert.pem --key \$HOME/key.pem

See voms-proxy-init --help or the man page for a complete list of available options.

Showing VOMS attributes information  

Once a proxy has been created, the voms-proxy-info command allowes the user to retrieve several information from it. The two most basic uses are:

$ voms-proxy-info
subject : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini/CN=proxy
issuer : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini
identity : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini
type : proxy
strength : 512 bits
path : /tmp/x509up_u502
timeleft : 10:33:52

which, as you can see, prints the same information that would be printed by a plain grid-proxy-info, and then there is:

$ voms-proxy-info --all
subject : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini/CN=proxy
issuer : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini
identity : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini
type : proxy
strength : 512 bits
path : /tmp/x509up_u502
timeleft : 11:59:59
=== VO valerio extension information ===
VO : valerio
subject : /C=IT/O=INFN/OU=Personal Certificate/L=CNAF/CN=Vincenzo Ciaschini
issuer : /C=IT/O=INFN/OU=Host/L=CNAF/CN=datatag6.cnaf.infn.it
attribute : /valerio
attribute : /valerio/asdasd
attribute : /valerio/qwerty
attribute : attributeOne = 111 (valerio)
attribute : attributeTwo = 222 (valerio)
timeleft : 11:59:59
uri : datatag6.cnaf.infn.it:15000

which prints everything that there is to know about the proxy and the included ACs.

Several options enable the user to select just a subset of the information shown here. See voms-proxy-info --help or the man page for a complete list of available options.

Destroying a proxy  

The voms-proxy-destroy command erases an existing proxy from the system. Its basic use is:

$ voms-proxy-destroy

See voms-proxy-destroy --help or the man page for a complete list of available options.