Safe Replacement Of Binaries And Libraries

When executable files are executed, only the pages that are actually used are loaded into memory. Other pages will be loaded only when commands written in them need to be executed.

If we copy a new executable on top of an old one, the same file's contents is being replaced. If a process running this executable then needs to load a page from disk, it might load some random page (cause the contents were changed), usually leading to its crash.

Lesson - first remove the old file (using 'rm'), and only then copy the new file to the same directory. don't worry - the file is removed from the directory, but will be erased from disk only when all processes close it.