What happens to a file descriptor when a process forks?

When a process is forked, the file descriptor is copied to the child process, meaning both processes (parent and child) have descriptors pointing to the same open file. However, the reference count on the descriptor increases, and the read/write position in the file is shared, so changes to the position in one process affect the other.

This means that if both processes are reading or writing to the file, access must be carefully synchronized to avoid conflicts or unpredictable behavior.