# How Patch Manager operations work
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This section provides technical details that explain how Patch Manager, a tool in Amazon Systems Manager, determines which patches to install and how it installs them on each supported operating system. For Linux operating systems, it also provides information about specifying a source repository, in a custom patch baseline, for patches other than the default configured on a managed node. This section also provides details about how patch baseline rules work on different distributions of the Linux operating system.

**Note**  
The information in the following topics applies no matter which method or type of configuration you are using for your patching operations:  
A patch policy configured in Quick Setup
A Host Management option configured in Quick Setup
A maintenance window to run a patch `Scan` or `Install` task
An on-demand **Patch now** operation