Question

If I chdir within a thread, will that affect the cwd of the parent program?

Answer 1

Yes.

If you need relative paths in a multithreaded application, it’s safest to use the at() versions of functions. For example, openat() is like open():

int openat(int dirfd, const char *pathname, int flags);

The first parameter is the fd to a directory. The path is relative to that directory.