fork(2)                   SYSTEM CALLS                    fork(2)



NAME
     fork - create a new process

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

     pidt fork(void);

DESCRIPTION
     fork causes creation of a  new  process.   The  new  process
     (child  process)  is  an  exact  copy of the calling process
     (parent process).  This means the child process inherits the
     following attributes from the parent process:

          real user ID, real group ID, effective user ID,  effec-
          tive group ID
          environment
          close-on-exec flag [see exec(2)]
          signal  handling  settings  (i.e.,  SIGDFL,   SIGIGN,
          SIGHOLD, function address)
          supplementary group IDs
          set-user-ID mode bit
          set-group-ID mode bit
          profiling on/off status
          nice value [see nice(2)]
          scheduler class [see priocntl(2)]
          all attached shared memory segments [see shmop(2)]
          process group ID
          session ID [see exit(2)]
          current working directory
          root directory
          file mode creation mask [see umask(2)]
          resource limits [see getrlimit(2)]
          controlling terminal

     Scheduling priority and any per-process  scheduling  parame-
     ters  that  are  specific to a given scheduling class may or
     may not be inherited according to the policy of that partic-
     ular class [see priocntl(2)].

     The child process differs from the  parent  process  in  the
     following ways:

          The child process has a unique process  ID  which  does
          not match any active process group 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 file
          descriptors and directory streams.  Each of the child's



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fork(2)                   SYSTEM CALLS                    fork(2)



          file descriptors shares a common file pointer with  the
          corresponding file descriptor of the parent.

          All semadj values are cleared [see semop(2)].

          Process locks, text locks and data locks are not inher-
          ited by the child [see plock(2)].

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

          The time left until an alarm clock signal is  reset  to
          0.

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

     Record locks set by the parent process are not inherited  by
     the child process [see fcntl(2)].

     fork will fail and no child process will be created  if  one
     or more of the following are true:

     EAGAIN         The system-imposed limit on the total  number
                    of processes under execution by a single user
                    would be exceeded.

     EAGAIN         Total amount of system memory available  when
                    reading  via  raw I/O is temporarily insuffi-
                    cient.

     ENOMEM         There is not enough swap space.

SEE ALSO
     alarm(2),   exec(2),   fcntl(2),   getrlimit(2),    nice(2),
     plock(2),  priocntl(2),  ptrace(2), semop(2), shmop(2), sig-
     nal(2), times(2), umask(2), wait(2), system(3S).

DIAGNOSTICS
     Upon successful completion, fork returns a value of 0 to the
     child  process  and returns the process ID of the child pro-
     cess to the parent process.  Otherwise, a value of (pidt)-1
     is  returned  to  the  parent  process,  no child process is
     created, and errno is set to indicate the error.










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