24.6. Summary

The fork() system call creates a new process (the child) by making an almost exact duplicate of the calling process (the parent). The vfork() system call is a more efficient version of fork(), but is usually best avoided because of its unusual semantics, whereby the child uses the parent’s memory until it either performs an exec() or terminates; in the meantime, execution of the parent process is suspended.

After a fork() call, we can’t rely on the order in which the parent and the child are next scheduled to use the CPU(s). Programs that make assumptions about the order of execution are susceptible to errors known as race conditions. Because the occurrence of such errors depends on external factors such as system load, they can be difficult to find and debug.