fork - create a new process
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 starts with no pending signals and an inactive alarm
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.
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. (The kernel variable NR_PROCS in
<minix/config.h> (Minix), or <minix/const.h> (Minix-vmd).)
[ENOMEM] There is insufficient (virtual) memory for the new