When a client computer has a maintenance window policy set, the following evaluation is made before an advertised program is be launched by Configuration Manager 2007:

• Is the available time left in the defined maintenance window greater or equal to (>=) the Maximum allowed run time for the advertised program plus (+) the Advertised Programs Client Agent countdown duration?
  
  

If the answer is yes, the advertised program will run; if not, Configuration Manager will wait until the next scheduled maintenance window in which there is sufficient time available.

Important
Any advertised program will fail to run when the maintenance windows that are defined on the client computer are set for a period less than that program's Maximum allowed run time setting. In this case, a status message will alert the user that the advertised program will not run.

Advertised programs with the Maximum allowed run time option set to Unknown can run past the end of maintenance windows. Because the program maximum allowed runtime (the program duration) is set to Unknown, client computers in the targeted collection will not evaluate the program runtime against the defined maintenance windows.

For additional information about program running sequences when using maintenance windows, including several sample scenarios, see the Program Run Scenarios Using Maintenance Windows topic in the System Center Configuration Manager 2007 documentation.

Maintenance windows are off by default, but can be set by administrators with security permissions. Permissions for setting or overriding maintenance windows must be granted separately from other security rights for a collection. These can only be granted by a site administrator.

Maintenance windows are not intended to function as a primary scheduling method for programs. Instead, they are designed to limit the interference of software deployments or changes with critical system functions.

For example, one likely use of a maintenance window would be to specifically restrict system changes on a collection of client computers to the period between midnight and 2:00 A.M., when network traffic is at a minimum or when those computers are not engaged in other activities.

It is recommended that if you use maintenance windows to restrict system changes, you should create specific collections for this purpose rather than using the default collections. Additionally, naming these new collections in a specific manner (such as "MW-<window name>") can be helpful. One or both of these methods will help you manage your collections more easily.

When using maintenance windows on your network, it will not be uncommon for a client computer to be a member of more than one collection with active maintenance windows on them. When this happens, client computers that are members of two or more collections with active maintenance windows will adhere to all defined windows.

Depending on when each of the separate maintenance windows is set to occur, this can have differing impact on running programs on a client computer:

If the maintenance windows occur at different times and do not overlap, the client computer will have two (or more) separate maintenance windows on them. Each window will function independently and will be self-contained.

If the maintenance windows occur at different times but overlap, the client will effectively have a single maintenance window that encompasses the period covered by both active windows. In this way, a client that has two maintenance windows of 1 hour each that overlap by 30 minutes would have an effective maintenance window of 90 minutes. This window will behave as if it were 90 minutes long, with respect to allowing programs to run or restarts to occur.

Note

Because the client software forecasts system restarts based on the next available maintenance window (and not based on combined or merged windows), administrators might receive an inaccurate status message saying "...the program may never reboot..." (ID 10079). However, the actual run-time evaluation of programs and restarts is done based on the combined maintenance window. When there is enough time from a combined or merged window, the system will restart, despite that status message.

The goal of maintenance windows is to limit program runs and system restarts outside of set windows. Certain types of Configuration Manager network usage are not bound by any maintenance windows that are set, including:

• Advertisements specifically set to ignore maintenance windows while running or restarting the client computer
  
  
• Some types of content downloads and advanced downloads
  
  
• Policy downloads
  
  
• Inventory data and data collection
  
  
• Baseline evaluation
  
  

If a program is set with Unknown as its Maximum allowed run time, it is not bound by the length of a maintenance window if the client countdown period is within the time left in the maintenance window.

Additionally, if settings (such as Restart Countdown) that utilize or affect the maintenance window are changed while the maintenance window is open, those changes will not be considered until the next applicable maintenance window. For example, if a maintenance window is currently open and has 4 minutes remaining in it, and the Restart Countdown is changed from 5 minutes to 1 minute, a queued program will not run in that maintenance window, even if it would otherwise have run with the new Restart Countdown.

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