Gdb breakpoint in background mode

Question

I'm trying to set breakpoing (break ) after attaching to process in background mode (attach &). However I got Cannot insert breakpoint 1. Cannot access memory at address 0x5560c872b71a Any reason why it's happening? Setting breakpoint in foreground mode is fine. Program was written in C++.

Answer 1

Any reason why it's happening?

The program must be stopped when inserting a breakpoint into it. Inserting a breakpoint is not an atomic operation, and writing to program code (which is what breakpoint insertion amounts to) while that code is executing may result in all kind of badness.

Use interrupt command to stop the process and bring it to foreground, insert your breakpoint, then continue & to put it into background again.