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OpenSolaris 2009.06 - man page for fork (opensolaris section 2)

fork(2) 				   System Calls 				  fork(2)

       fork, fork1, forkall, forkx, forkallx - create a new process

       #include <sys/types.h>
       #include <unistd.h>

       pid_t fork(void);

       pid_t fork1(void);

       pid_t forkall(void);

       #include <sys/fork.h>

       pid_t forkx(int flags);

       pid_t forkallx(int flags);

       The  fork(),  fork1(),  forkall(), forkx(), and forkallx() functions create a new process.
       The address space of the new process (child process) is an exact copy of the address space
       of  the	calling  process  (parent  process).  The  child  process  inherits the following
       attributes from the parent process:

	   o	  real user ID, real group ID, effective user ID, effective group ID

	   o	  environment

	   o	  open file descriptors

	   o	  close-on-exec flags (see exec(2))

	   o	  signal  handling  settings  (that  is,  SIG_DFL,  SIG_IGN,  SIG_HOLD,  function

	   o	  supplementary group IDs

	   o	  set-user-ID mode bit

	   o	  set-group-ID mode bit

	   o	  profiling on/off status

	   o	  nice value (see  nice(2))

	   o	  scheduler class (see priocntl(2))

	   o	  all attached shared memory segments (see shmop(2))

	   o	  process group ID -- memory mappings (see mmap(2))

	   o	  session ID (see exit(2))

	   o	  current working directory

	   o	  root directory

	   o	  file mode creation mask (see umask(2))

	   o	  resource limits (see	getrlimit(2))

	   o	  controlling terminal

	   o	  saved user ID and group ID

	   o	  task ID and project ID

	   o	  processor bindings (see processor_bind(2))

	   o	  processor set bindings (see pset_bind(2))

	   o	  process privilege sets (see getppriv(2))

	   o	  process flags (see getpflags(2))

	   o	  active contract templates (see contract(4))

       Scheduling priority and any per-process scheduling parameters that are specific to a given
       scheduling class might or might not be inherited according to the policy of that  particu-
       lar  class  (see priocntl(2)). The child process might or might not be in the same process
       contract as the parent (see process(4)). The child process differs from the parent process
       in the following ways:

	   o	  The  child  process  has  a  unique  process ID which does not match any active
		  process group ID.

	   o	  The child process has a different parent process ID (that is, the process ID of
		  the parent process).

	   o	  The  child process has its own copy of the parent's file descriptors and direc-
		  tory streams. Each of the child's file descriptors shares a common file pointer
		  with the corresponding file descriptor of the parent.

	   o	  Each	shared	memory	segment  remains attached and the value of shm_nattach is
		  incremented by 1.

	   o	  All semadj values are cleared (see semop(2)).

	   o	  Process locks, text locks, data locks, and other memory locks are not inherited
		  by the child (see plock(3C) and memcntl(2)).

	   o	  The  child  process's  tms  structure is cleared: tms_utime, stime, cutime, and
		  cstime are set to 0 (see times(2)).

	   o	  The child processes resource utilizations are set to 0; see  getrlimit(2).  The
		  it_value  and  it_interval values for the ITIMER_REAL timer are reset to 0; see

	   o	  The set of signals pending for the child process is initialized  to  the  empty

	   o	  Timers created by timer_create(3C) are not inherited by the child process.

	   o	  No  asynchronous  input  or asynchronous output operations are inherited by the

	   o	  Any preferred hardware address tranlsation sizes (see memcntl(2)) are inherited
		  by the child.

	   o	  The child process holds no contracts (see contract(4)).

       Record  locks  set  by  the  parent  process  are  not inherited by the child process (see

       Although any open door descriptors in the parent are shared by the child, only the  parent
       will  receive  a  door  invocation from clients even if the door descriptor is open in the
       child. If a descriptor is closed in the parent, attempts to operate on the door descriptor
       will fail even if it is still open in the child.

       A  call to forkall() or forkallx() replicates in the child process all of the threads (see
       thr_create(3C) and pthread_create(3C)) in the parent process. A call to fork1() or forkx()
       replicates only the calling thread in the child process.

       A  call to fork() is identical to a call to fork1(); only the calling thread is replicated
       in the child process. This is the POSIX-specified behavior for fork().

       In releases of Solaris prior to Solaris 10, the behavior of fork() depended on whether  or
       not  the  application was linked with the POSIX threads library. When linked with -lthread
       (Solaris Threads) but not linked with -lpthread (POSIX Threads), fork() was  the  same  as
       forkall().   When  linked with -lpthread, whether or not also linked with -lthread, fork()
       was the same as fork1().

       Prior to Solaris 10, either -lthread or -lpthread was required for multithreaded  applica-
       tions.  This  is no longer the case. The standard C library provides all threading support
       for both sets of application programming interfaces.  Applications that require replicate-
       all fork semantics must call forkall() or forkallx().

   Fork Extensions
       The  forkx()  and  forkallx()  functions  accept  a flags argument consisting of a bitwise
       inclusive-OR of zero or more of the following flags,  which  are  defined  in  the  header


	   Do  not post a SIGCHLD signal to the parent process when the child process terminates,
	   regardless of the disposition of the SIGCHLD signal in the parent. SIGCHLD signals are
	   still  possible  for job control stop and continue actions if the parent has requested


	   Do not allow wait-for-multiple-pids by the parent, as  in  wait(),  waitid(P_ALL),  or
	   waitid(P_PGID),  to	reap  the child and do not allow the child to be reaped automati-
	   cally due the disposition of the SIGCHLD signal being set to be ignored in the parent.
	   Only  a  specific  wait  for the child, as in waitid(P_PID, pid), is allowed and it is
	   required, else when the child exits it will remain a zombie until the parent exits.

       If the flags argument is 0 forkx() is identical to fork() and forkallx() is  identical  to

   fork() Safety
       If  a multithreaded application calls fork(), fork1(), or forkx(), and the child does more
       than simply call one of the exec(2) functions, there is a possibility of  deadlock  occur-
       ring  in  the  child.  The application should use pthread_atfork(3C) to ensure safety with
       respect to this deadlock. Should there be any outstanding mutexes throughout the  process,
       the  application  should call pthread_atfork() to wait for and acquire those mutexes prior
       to calling fork(), fork1(), or forkx(). See  "MT-Level of Libraries" on the  attributes(5)
       manual page.

       The pthread_atfork() mechanism is used to protect the locks that libc(3LIB) uses to imple-
       ment interfaces such as malloc(3C).  All interfaces provided by libc are safe to use in	a
       child process following a fork(), except when fork() is executed within a signal handler.

       The  POSIX  standard  (see  standards(5))  requires  fork  to  be  Async-Signal-Safe  (see
       attributes(5)). This cannot be made to happen with fork handlers in  place,  because  they
       acquire	locks.	To  be	in nominal compliance, no fork handlers are called when fork() is
       executed within a signal context.  This leaves the child process in a  questionable  state
       with  respect  to  its  locks,  but  at	least the calling thread will not deadlock itself
       attempting to acquire a lock that it already owns.  In  this  situation,  the  application
       should  strictly  adhere to the advice given in the POSIX specification: "To avoid errors,
       the child process may only execute Async-Signal-Safe operations until such time as one  of
       the exec(2) functions is called."

       Upon  successful  completion, fork(), fork1(), forkall(), forkx(), and forkallx() return 0
       to the child process and return the process ID of the child process to the parent process.
       Otherwise,  (pid_t)-1  is returned to the parent process, no child process is created, and
       errno is set to indicate the error.

       The fork(), fork1(), forkall(), forkx(), and forkallx() functions will fail if:

       EAGAIN	 A resource control or	limit on the total number of  processes,  tasks  or  LWPs
		 under	execution  by a single user, task, project, or zone has been exceeded, or
		 the total amount of system  memory  available	is  temporarily  insufficient  to
		 duplicate this process.

       ENOMEM	 There is not enough swap space.

       EPERM	 The {PRIV_PROC_FORK} privilege is not asserted in the effective set of the call-
		 ing process.

       The forkx() and forkallx() functions will fail if:

       EINVAL	 The flags argument is invalid.

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       |Interface Stability	     |Committed 		   |
       |MT-Level		     |Async-Signal-Safe.	   |
       |Standard		     |See below.		   |

       For fork(), see standards(5).

       alarm(2), exec(2), exit(2), fcntl(2),  getitimer(2),  getrlimit(2),  memcntl(2),  mmap(2),
       nice(2),  priocntl(2), semop(2), shmop(2), times(2), umask(2), waitid(2), door_create(3C),
       exit(3C),  plock(3C),  pthread_atfork(3C),  pthread_create(3C),	signal(3C),   system(3C),
       thr_create(3C)  timer_create(3C), wait(3C), contract(4), process(4), attributes(5), privi-
       leges(5), standards(5)

       An application should call _exit() rather than  exit(3C)  if  it  cannot  execve(),  since
       exit() will flush and close standard I/O channels and thereby corrupt the parent process's
       standard I/O data structures. Using exit(3C) will flush buffered data twice. See exit(2).

       The thread in the child that calls fork(), fork1(), or fork1x() must  not  depend  on  any
       resources  held by threads that no longer exist in the child. In particular, locks held by
       these threads will not be released.

       In a multithreaded process, forkall() in one thread can cause blocking system calls to  be
       interrupted and return with an EINTR error.

SunOS 5.11				   28 Oct 2008					  fork(2)

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