22.2.1 Understanding the SEV

The Security Equivalence Vector (SEV) is calculated for each NSS user based on information in the user’s profile in Novell eDirectory. It is a list of eDirectory GUIDs, for example:

After you boot the Linux server, when a user first attempts to connect to the NSS file system, NSS contacts Novell eDirectory to retrieve the user’s Security Equivalence Vector (SEV). eDirectory calculates the user’s effective rights for the NSS volume, creates the SEV, and passes it to NSS. NSS compares the user’s SEV with file system trustees and trustee rights for the specified file or directory to determine if the user can access the resource.

For NetWare, whenever a user connects to the NSS file system, NetWare retrieves the user’s SEV from eDirectory and maintains it as part of the connection structure for the user’s session. NSS automatically retrieves the user’s SEV from the NetWare connection structure, then deletes it when the session ends.

On Linux, the SEV behavior differs because NSS does not have the same integrated relationship to the connection infrastructure as it does on NetWare. NSS caches the SEV locally in the server memory, where it remains until the server is rebooted or the user is deleted from eDirectory. NSS polls eDirectory at a specified interval for updates to the SEVs that are in cache.

22.2.2 Enabling or Disabling the Background SEV Update for NSS Volumes on Linux

By default, the SEV is updated in the background and whenever the server is rebooted. You can optionally disable the background updating. If it is disabled, the user access can become unsynchronized over time, so that users might have less or more access than you have configured. We recommend that you leave the SEV updating feature enabled, then modify the polling frequency to best meet the security needs of your production environment.

To enable or disable the setting:

The SEV Update is enabled when you first reboot the server. If you disable SEV updates and want the setting to persist across server reboots, include the /SecurityEquivalenceUpdating option in the /etc/opt/novell/nss/nssstart.cfg file.

22.2.3 Configuring the Background SEV Update Interval

You might want to modify the background SEV update interval to make the polling for eDirectory updates to be more or less frequent. Polling too frequently can impact performance. Polling too infrequently can cause delays in granting or restricting access for certain users. To avoid possible security violations, you can also force an update at any time by using the /ForceSecurityEquivalenceUpdate command. For information, see Section 22.2.4, Forcing a Background SEV Update.

The interval for the background updating of the SEV is the elapsed time between the last update and the next one. At the end of the elapsed time, NSS requires updated SEVs from eDirectory. The default interval is 7200 seconds (2 hours). The valid range is 300 (5 minutes) to 7776000 (90 days).

To set the interval to use until the next server reboot:

To make the interval setting persistent across server reboots, include the /UpdateSecurityEquivalenceInterval=value option in the /etc/opt/novell/nss/nssstart.cfg file.

22.2.4 Forcing a Background SEV Update

If you modify user’s access control settings or remove a user from eDirectory in between SEV update intervals, you can to force the SEV to be updated immediately after that to avoid possible security violations. Use the /ForceSecurityEquivalenceUpdate option to force an immediate update for all users in the NSS file system so that your changes can be reflected immediately in the user’s active SEV for this server.

To force an immediate update: