Attach to local process feature allows you to debug a project which you are developing in CLion, but (for some reasons) are not able to launch directly from your IDE.
Currently in CLion you can attach to local process with GDB on Windows and Linux or LLDB on macOS for the C/C++ applications and Python debugger for the Python scripts and use all the debugging instruments available in CLion.
Prerequisites for Ubuntu users
If you are using CLion on Ubuntu (or probably, on some other Linux distribution), upon the first attempt to attach to the local process you can get the ptrace: Operation not permitted. error message. To disable it and enable attach to the local process feature, do the following:
To disable this restriction temporarily, enter the command:
echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope
To disable this restriction permanently, open the file /etc/sysctl.d/10-ptrace.conf for editing and change the line kernel.yama.ptrace_scope = 1 to kernel.yama.ptrace_scope = 0. To apply the changes, enter sudo service procps restart or restart your system, at your choice.
To attach to a local process, follow these general steps:
Launch the process intended for debugging. You can do it from operating system or using the CLion terminal.
To find the process to attach to, do one of the following:
On the main menu, choose Run | Attach to Local Process:
On the main menu, choose Help | Find Action or press Ctrl+Shift+A. In the list of actions that appears, find the desired action by typing the first letters, and select it:
From the list of available processes that appears, select the desired process. Simplify your search by typing the first letters of its name or PID or for a Python script:
of the Debug Tool Window . 
