When you try to change a file that’s currently running, it used to say text file busy. Example:

First terminal:

$ cc -Wall -Wextra -o test test.c
$ cp test run
$ ./run

Second terminal:

$ cp test run
cp: cannot create regular file 'run': Text file busy

But on my machines today, it crashes the running program. 🤨 As soon as I run the cp, I get a coredump:

$ ./run
... time passes, I do "cp test run" in a second terminal ...
Bus error (core dumped)

How odd. Another mystery to solve …