FORK(2) Linux Programmer s Manual FORK(2)

NAME fork - create a child process

SYNOPSIS #include <sys/types.h> #include <unistd.h>

pid_t fork(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 that it incurs is the time and memory required to dupli- cate 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 parents thread of execution, and a 0 is returned in the childs thread of exe- cution. 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 parents page tables and allocate a task structure for the child.

EAGAIN It was not possible to create a new process because the callers RLIMIT_NPROC resource limit was encountered. To exceed this limit, the process must have either the CAP_SYS_ADMIN or the CAP_SYS_RESOURCE capability.

ENOMEM fork() failed to allocate the necessary kernel structures because memory is tight.

CONFORMING TO SVr4, 4.3BSD, POSIX.1-2001.

EXAMPLE See pipe(2) and wait(2).

SEE ALSO clone(2), execve(2), setrlimit(2), unshare(2), vfork(2), wait(2), capa- bilities(7)

Linux 2.6.6 2004-05-27 FORK(2)