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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():  XPG4-UNIX, XSH5.0

  vfork():  XPG4-UNIX, 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 segments

    ·  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 corresponding 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.

    ·  [XPG4-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
  The fork() and vfork() functions are supported for multithreaded
  applications.

  If a multithreaded process calls the fork() or vfork() function, 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
  operations it knows will not cause deadlock until one of the exec functions
  is called.




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:

  [EAGAIN]  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.

  [ENOMEM]  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), raise(3), times(3), ulimit(3)

  Standards: standards(5)

Index for Section 2

Alphabetical listing for F

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