Attach to process
JetBrains Rider provides a way to attach the debugger to both local and remote processes.
The steps to attach to a process depend on how and where the process was launched.
First off, if you want to debug a program that can be started from JetBrains Rider, the best way to do so is to start a local debugging session.
Attach to a local process
Press Ctrl+Alt+F5 or choose from the main menu.
JetBrains Rider will show the list of the running local processes. Select the process to attach to.
If necessary, narrow down the list of processes by typing the first letters of its name or PID. If the target process was started after you'd opened this dialog, you may need to click Refresh
. 
If you don't know the name or ID of the desired process, try the following:
Click Show as: Tree on the toolbar and start with expanding the parent process nodes.
Select a specific debugger in the top-right corner of the dialog. For example, if you are debugging a .NET process, select .NET to hide all native and JVM processes.
To connect to the process with the default debugger, press Enter. If there are several debuggers that can be used for the process, you can choose the debugger with the selector in the bottom-right corner of the dialog.
If you don't have sources of the target .NET process, you can still attach to it either as described above or by clicking Attach to Process on the Welcome screen, right after you start the IDE. JetBrains Rider will automatically load and decompile all assemblies from the process.
To get a proper starting point for debugging the target process, you can search for types in the loaded assemblies and set breakpoints in the decompiled code.
Attach to a remote process
Debugging a remote process (usually, a Web application running on a remote host), is a completely different scenario, which requires setting up the debug agent on the remote host and configuring the connection before actually attaching to the target process. All those steps are described in the Debug remote applications via SSH tutorial.
Detach from a process
The procedure to detach from a remote process is the same as for stopping a local debug session, however, the effect is different. When you detach, the debugging session closes but the process continues to run.
Click the Stop
button on the main toolbar on in the Debug window.Alternatively, click Stop
on the main toolbar or press Ctrl+F2, then select the session to be closed.