# 4.12. Installing custom components

By default, Open MPI looks in two places for components at run-time (in order):

1. `$prefix/lib/openmpi/`: This is the system-provided components directory, part of the installation tree of Open MPI itself.

2. `$HOME/.openmpi/components/`: This is where users can drop their own components that will automatically be “seen” by Open MPI at run-time. This is ideal for developmental, private, or otherwise unstable components.

Note that the directories and search ordering used for finding components in Open MPI is, itself, an MCA parameter. Setting the `mca_component_path` changes this value (a colon-delimited list of directories).

Note also that components are only used on nodes where they are “visible”. Hence, if your `$prefix/lib/openmpi/` is a directory on a local disk that is not shared via a network filesystem to other nodes where you run MPI jobs, then components that are installed to that directory will only be used by MPI jobs running on the local node.

More specifically: components have the same visibility as normal files. If you need a component to be available to all nodes where you run MPI jobs, then you need to ensure that it is visible on all nodes (typically either by installing it on all nodes for non-networked filesystem installs, or by installing them in a directory that is visible to all nodes via a networked filesystem). Open MPI does not automatically send components to remote nodes when MPI jobs are run.