FORK(2)

NAME
fork - spawn new process

SYNOPSIS
fork( )

DESCRIPTION
Fork and vfork(2) are the only ways new processes are created. With fork , the new process's core image is a copy of that of the caller of fork. The only distinction 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.

Vfork is the most efficient way of creating a new process when the fork is to be followed shortly by an exec, but is not suitable when the fork is not to be followed by an exec.

SEE ALSO
wait(2), exec(2), vfork(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 (PDP-11)
(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 created.