Mac OS X Server: How To Adjust The NetBoot Client Aging Time

This document explains how to adjust the aging time of the NetBoot AFP User Binding in order to allow a greater number of NetBoot clients to access the NetBoot server.
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NetBoot clients bind to the NetBoot server using an AFP User as part of the NetBoot process. There are a finite number of AFP User bindings available to NetBoot clients in order to provide the optimal mix of network performance and number of clients.

It is possible to adjust the interval at which the AFP bindings can be reclaimed and used for another NetBoot client upon startup. In larger installations, adjusting this interval or aging time below the default setting of 24 hours (86400 seconds) provides NetBoot clients with "reclaimed" AFP bindings with greater frequency. This strategy can be used to effectively increase the number of NetBoot clients that can be served by a NetBoot server.

The default aging time for a NetBoot client is 24 hours. This can be modified by setting the NetInfo property: age_time_seconds

This property is in the local NetInfo domain in the "config" property at: /config/NetBootServer.

The main reason why aging/reclamation was added was to solve the issue of NetBoot client turnover. For example, suppose 50 NetBoot clients were started up initially, then two of the clients were removed or replaced with two other units. Without aging/reclamation, the administrator would need to manually reset the bindings in order to be able to NetBoot 50 clients again.

A NetBoot client that has not started up in the last interval of time as defined by "age_time_seconds" may have its AFP user binding reclaimed. If the server runs out of AFP User logins when servicing a NetBoot request, it may reclaim an AFP User login from one of the other NetBoot clients that has already started up. The reclamation process does not disrupt any existing, started up NetBoot systems as long as they remain turned on.

The side effect of setting the aging time to a very small value (5 minutes, for example) means that it is pretty easy to end up with multiple clients using the same AFP login, thus increasing the number of clients that the NetBoot server will serve. However, should all NetBoot clients that are currently started up from the NetBoot server restart simultaneously, they will still be limited by the maximum number of AFP logins. The maximum number of AFP logins is set in the property afp_users_max (also in /config/NetBootServer).

The preferred method of modifying the aging/reclamation value in the NetInfo database is using the niutil command in the terminal application. NetInfo Manager can also be used to modify these properties and values.

If you wish to change these settings, follow these steps:
    1. Open Terminal (/Applications/Utilities).
    2. Type: niutil -create . /config/NetBootServer
    Note: If the directory already exists, this command is unnecessary. Go to the next step.
    3. Press Return.
    4. Type: niutil -createprop . /config/NetBootServer age_time_seconds 300
    Note: Be sure to calculate the time in seconds. In this example, 300 seconds gives you a five minute age time. You may substitute another value.
    5. Press Return.
    6. Quit Terminal.

For more information see, technical document 122015, "Mac OS X Server Administration Guide: Manual".

Published Date: Feb 17, 2012