The fork(2) function causes creation of a new
process. The new process (child process) is an exact copy of the
calling process (parent 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(2) or write(2) 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 process's values of tms_utimetms_stimetms_cutime and tms_cstime are set to zero.
The child does not inherit any file locks set by the
parent.
Any pending alarms have been cleared for the child
process.
Signals pending for the child process have been initialized to
the empty set.
Upon successful completion, fork(2) 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.