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fork(2)                          System Calls                          fork(2)



NAME
       fork, fork1, forkall - create a new process

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

       pid_t fork(void);

       pid_t fork1(void);

       pid_t forkall(void);

DESCRIPTION
       The  fork(), fork1(), and forkall() 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 address)

         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 particular 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  descrip-
            tors  and  directory streams. Each of the child's file descriptors
            shares a common file pointer with the corresponding file  descrip-
            tor 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  getr-
            limit(2).  The it_value and it_interval values for the ITIMER_REAL
            timer are reset to 0; see getitimer(2).

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

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

         o  No asynchronous input or asynchronous output operations are inher-
            ited by the child.

         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 fcntl(2)).

       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.

   Threads
       A  call to forkall() 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()  replicates  only  the  calling  thread  in the child
       process.

       In Solaris 10, 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 previous releases of Solaris, 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().

       In  Solaris  10,  neither -lthread nor -lpthread is required for multi-
       threaded applications. The standard C library  provides  all  threading
       support  for both sets of application programming interfaces.  Applica-
       tions that require replicate-all fork semantics must call forkall().

   fork() Safety
       If a multithreaded application calls fork() or fork1(), and  the  child
       does  more  than  simply  call one of the exec(2) functions, there is a
       possibility of deadlock occurring 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()  or  fork1().  See   "MT-Level   of
       Libraries" on the attributes(5) manual page.

RETURN VALUES
       Upon  successful completion, fork(), fork1(), and forkall() 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.

ERRORS
       The fork(), fork1(), and forkall()function 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 calling process.



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


       tab()     allbox;     cw(2.750000i)|    cw(2.750000i)    lw(2.750000i)|
       lw(2.750000i).  ATTRIBUTE  TYPEATTRIBUTE  VALUE  Interface  StabilityT{
       fork()  is  Standard.  fork1()  and  forkall() are Stable.  T} MT-Leve-
       lAsync-Signal-Safe.


SEE ALSO
       alarm(2), exec(2), exit(2), fcntl(2), getitimer(2), getrlimit(2),  mem-
       cntl(2),  mmap(2),  nice(2), priocntl(2), semop(2), shmop(2), times(2),
       umask(2), door_create(3DOOR), exit(3C), plock(3C),  pthread_atfork(3C),
       pthread_create(3C),  signal(3C),  system(3C), thr_create(3C) timer_cre-
       ate(3RT),  wait(3C),   contract(4),   process(4)attributes(5),   privi-
       leges(5), standards(5)

NOTES
       An  applications  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() or fork1() 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 5.10                        19 Jul 2004                          fork(2)