system call 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,
except for descriptors returned by
which are not inherited from the parent process.
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
on a descriptor in the child process can affect a subsequent
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' resource utilizations
are set to 0; see
- All interval timers are cleared; see
- The child process has only one thread,
corresponding to the calling thread in the parent process.
If the process has more than one thread,
locks and other resources held by the other threads are not released
and therefore only async-signal-safe functions
are guaranteed to work in the child process until a call to
or a similar function.