Run keys cause programs to automatically run each time that a user logs on. The Windows XP registry includes the following four Run keys:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunOnce
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\RunOnce

Each of these keys has a series of values. The values allow multiple entries to exist without overwriting one another. The data value for a value is a command line.

There are some special considerations for the third and fourth keys in the list, the RunOnce keys:

1. By default, Run keys are ignored when the computer starts in Safe mode. Under the RunOnce keys, you can prefix a value name with an asterisk (*) to force the associated program to run even in Safe mode.
2. You can prefix a RunOnce value name with an exclamation point (!) to defer deletion of the value until after the command runs.
3. Without the exclamation point prefix, a RunOnce value is deleted before the command runs. As a result, if a RunOnce operation does not run properly, the associated program is not asked to run the next time you start the computer.

If more than one program is registered under any particular key, the order in which those programs are run is indeterminate. A program run from any of these keys should not write to the key during its execution. Doing so will interfere with the execution of other programs registered under the key. Furthermore, applications should use the RunOnce keys only for transient conditions (such as to complete application setup); an application must not continually re-create entries under RunOnce. Doing so will interfere with Windows Setup.