fork(2) 							System Calls Manual							   fork(2)

NAME

       fork, vfork - Creates a new process

SYNOPSIS

       #include <unistd.h>

       pid_t fork (void);
       pid_t vfork (void);

       Application  developers	may  want  to  specify an #include statement for <sys/types.h> before the one for <unistd.h> if programs are being
       developed for multiple platforms. The additional #include statement is not required on Tru64 UNIX systems or by ISO  or	X/Open	standards,
       but may be required on other vendors' systems that conform to these standards.

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       fork():	XSH5.0

       vfork():  XSH5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

DESCRIPTION

       The fork() and vfork() functions create a new process (child process) that is identical to the calling process (parent process).

       The  child  process inherits the following attributes from the parent process: Environment Close-on-exec flags Signal handling settings Set
       user ID mode bit Set group ID mode bit Trusted state Profiling on/off status Nice value All attached shared libraries Process group ID  tty
       group ID Current directory Root directory File mode creation mask File size limit Attached shared memory segments Attached mapped file seg-
       ments All mapped regions with the same protection and sharing mode as in the parent process Its own copy of  the  parent's  open  directory
       streams

       The  child process differs from the parent process in the following ways: The child process has a unique process ID that does not match any
       active process group ID.  The parent process ID of the child process matches the process ID of the parent.  The child process has  its  own
       copy of the parent process's file descriptors.  Each of the child's file descriptors refers to the same open file description with the cor-
       responding file descriptor of the parent process.  The child process has its own copy of the parent's open directory  streams.	Each  open
       directory  stream  in  the child process may share directory stream positioning with the corresponding directory stream of the parent.  All
       semadj values are cleared.  Process locks, text locks, and data locks are not inherited by the child process.  The child process' values of
       tms_utime,  tms_stime,  tms_cutime,  and  tms_cstime  are  set  to  0 (zero).  Any pending alarms are cleared in the child process.  [Tru64
       UNIX]  Any interval timers enabled by the parent process are reset in the child process.  Any signals pending for the  parent  process  are
       cleared for the child process.

NOTES

       If  a  multithreaded  process forks a child process, the new process contains a replica of the calling thread and its entire address space,
       possibly including the states of mutexes and other resources.  Consequently, to avoid errors, the child process should only execute  opera-
       tions it knows will not cause deadlock.

       The fork() and vfork() functions have essentially the same implementation at the level of the operating system kernel but may differ in how
       they are supported through different libraries.	Some libraries, such as libpthread and	libc,  support	fork  handler  routines  that  can
       acquire	and  release  resources  that  are critical to the child process. Fork handlers therefore allow an application to manage potential
       deadlock situations that might occur between the parent and child processes.  Fork handlers do not work correctly if the application  calls
       vfork() to create the child process.  Therefore, applications using libpthread and libc should call fork() to create a child process.

       For  more  information  about  fork  handler  routines, see pthread_atfork(3).  For a complete list of system calls that are reentrant with
       respect to signals, see signal(4).

RETURN VALUES

       Upon successful completion, the fork() and vfork() functions return a value of 0 (zero) to the child process and return the process  ID	of
       the child process to the parent process.  Otherwise, a value of -1 is returned to the parent, no child process is created, and errno is set
       to indicate the error.

ERRORS

       The fork() and vfork() functions set errno to the specified values for the following conditions: The limit on the total number of processes
       executing  for  a  single  user	would be exceeded.  This limit can be exceeded by a process with superuser privilege.  There is not enough
       space left for this process.

RELATED INFORMATION

       Functions: exec(2), exit(2), getpriority(2), getrusage(2), plock(2), ptrace(2),	semop(2),  shmat(2),  sigaction(2),  sigvec(2),  umask(2),
       wait(2)

       Routines: nice(3), pthread_atfork(3), raise(3), times(3), ulimit(3)

       Files: signal(4)

       Standards: standards(5) delim off

																	   fork(2)