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fork(2) [bsd man page]

FORK(2) 							System Calls Manual							   FORK(2)

fork - create a new process SYNOPSIS
pid = fork() int pid; DESCRIPTION
Fork causes creation of a new process. The new process (child process) is an exact copy of the calling process except for the following: The child process has a unique process ID. The child process has a different parent process ID (i.e., the process ID of the parent process). The child process has its own copy of the parent's descriptors. These descriptors reference the same underlying objects, so that, for instance, file pointers in file objects are shared between the child and the parent, so that an lseek(2) on a descriptor in the child process can affect a subsequent read or write by the parent. This descriptor copying is also used by the shell to establish standard input and output for newly created processes as well as to set up pipes. The child processes resource utilizations are set to 0; see setrlimit(2). RETURN VALUE
Upon successful completion, fork returns a value of 0 to the child process and returns the process ID of the child process to the parent process. Otherwise, a value of -1 is returned to the parent process, no child process is created, and the global variable errno is set to indicate the error. ERRORS
Fork will fail and no child process will be created if one or more of the following are true: [EAGAIN] The system-imposed limit on the total number of processes under execution would be exceeded. This limit is configuration- dependent. [EAGAIN] The system-imposed limit MAXUPRC (<sys/param.h>) on the total number of processes under execution by a single user would be exceeded. [ENOMEM] There is insufficient swap space for the new process. SEE ALSO
execve(2), wait(2) 3rd Berkeley Distribution May 22, 1986 FORK(2)

Check Out this Related Man Page

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

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 incurred by fork 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 parent's thread of execution, and a 0 is returned in the child's 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 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. CONFORMING TO
The fork call conforms to SVr4, SVID, POSIX, X/OPEN, BSD 4.3. SEE ALSO
clone(2), execve(2), vfork(2), wait(2) Linux 1.2.9 1995-06-10 FORK(2)
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