______ system call creates new process in Unix.

Answer: fork

Key idea: fork duplicates the calling process to create a new (child) process.

• What fork does: creates a child process that is a copy of the parent (same code, data, and open file descriptors).

• Return values: fork returns the child's process ID (positive integer) in the parent, returns 0 in the child, and returns -1 on error (setting errno).

• Common usage: programs often call exec (one of the exec family) in the child after fork to run a different program; the parent may wait for the child using wait or waitpid.

• Clarification: 'create', 'create new', and 'fork new' are not Unix system calls for creating processes. There is a file-creation call spelled creat (without the final 'e'), which creates files, not processes.