fork(2) [v7 man page]

FORK(2) 							System Calls Manual							   FORK(2)

NAME

       fork  -	spawn new process

SYNOPSIS

       fork( )

DESCRIPTION

       Fork  is  the only way new processes are created.  The new process's core image is a copy of that of the caller of fork.  The only distinc-
       tion is the fact that the value returned in the old (parent) process contains the process ID of the new (child) process,  while	the  value
       returned in the child is 0.  Process ID's range from 1 to 30,000.  This process ID is used by wait(2).

       Files open before the fork are shared, and have a common read-write pointer.  In particular, this is the way that standard input and output
       files are passed and also how pipes are set up.

SEE ALSO

       wait(2), exec(2)

DIAGNOSTICS

       Returns -1 and fails to create a process if: there is inadequate swap space, the user is not super-user and has too many processes, or  the
       system's process table is full.	Only the super-user can take the last process-table slot.

ASSEMBLER

       (fork = 2.)
       sys fork
       (new process return)
       (old process return, new process ID in r0)

       The return locations in the old and new process differ by one word.  The C-bit is set in the old process if a new process could not be cre-
       ated.

																	   FORK(2)

FORK(2) 							System Calls Manual							   FORK(2)

NAME

       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)