FORK Section: Linux Programmer's Manual (2) Updated: 10 June 2025 Index   NAME fork, vfork - create a child process   SYNOPSIS #include <unistd.h> pid_t fork(void); pid_t vfork(void);   DESCRIPTION fork creates a child process that differs from the parent process only in its PID and PPID, and in the fact that resource utilizations are set to 0. File locks and pending signals are not inherited. Under Linux, fork is implemented using copy-on-write pages, so the only penalty incurred by fork is the time and memory required to duplicate the parent's page tables, and to create a unique task structure for the child.   RETURN VALUE On success, the PID of the child process is returned in the parent's thread of execution, and a 0 is returned in the child's thread of execution. On failure, a -1 will be returned in the parent's context, no child process will be created, and errno will be set appropriately.   ERRORS EAGAIN fork cannot allocate sufficient memory to copy the parent's page tables and allocate a task structure for the child. ENOMEM fork failed to allocate the necessary kernel structures because memory is tight.   BUGS Under Linux, vfork is merely an alias for fork.   CONFORMING TO The fork call conforms to SVr4, SVID, POSIX, X/OPEN, BSD 4.3.   SEE ALSO   Index NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS BUGS CONFORMING TO SEE ALSO This document was created by using the manual pages. Time: 11:56:05 GMT, March 24, 2025