4.3BSD - /usr/man/cat2/fcntl.0

FCNTL(2)                                                              FCNTL(2)


NAME
       fcntl - file control

SYNOPSIS
       #include <fcntl.h>

       res = fcntl(fd, cmd, arg)
       int res;
       int fd, cmd, arg;

DESCRIPTION
       Fcntl  provides  for  control  over  descriptors.  The argument fd is a
       descriptor to be operated on by cmd as follows:

       F_DUPFD        Return a new descriptor as follows:

                      Lowest numbered available  descriptor  greater  than  or
                      equal to arg.

                      Same object references as the original descriptor.

                      New  descriptor  shares  the  same  file  pointer if the
                      object was a file.

                      Same access mode (read, write or read/write).

                      Same file status  flags  (i.e.,  both  file  descriptors
                      share the same file status flags).

                      The  close-on-exec  flag  associated  with  the new file
                      descriptor is set to remain open across execv(2)  system
                      calls.

       F_GETFD        Get  the  close-on-exec  flag  associated  with the file
                      descriptor fd.  If the low-order bit is 0, the file will
                      remain  open  across  exec,  otherwise  the file will be
                      closed upon execution of exec.

       F_SETFD        Set the close-on-exec flag associated with fd to the low
                      order bit of arg (0 or 1 as above).

       F_GETFL        Get descriptor status flags, as described below.

       F_SETFL        Set descriptor status flags.

       F_GETOWN       Get  the process ID or process group currently receiving
                      SIGIO and SIGURG signals; process groups are returned as
                      negative values.

       F_SETOWN       Set  the  process  or process group to receive SIGIO and
                      SIGURG signals; process groups are specified by  supply‐
                      ing  arg  as negative, otherwise arg is interpreted as a
                      process ID.

       The flags for the F_GETFL and F_SETFL flags are as follows:

       FNDELAY        Non-blocking I/O; if no data  is  available  to  a  read
                      call,  or  if  a  write  operation would block, the call
                      returns -1 with the error EWOULDBLOCK.

       FAPPEND        Force each write to append at the end  of  file;  corre‐
                      sponds to the O_APPEND flag of open(2).

       FASYNC         Enable  the SIGIO signal to be sent to the process group
                      when I/O is possible, e.g., upon availability of data to
                      be read.

RETURN VALUE
       Upon  successful  completion, the value returned depends on cmd as fol‐
       lows:
         F_DUPFD   A new file descriptor.
         F_GETFD   Value of flag (only the low-order bit is defined).
         F_GETFL   Value of flags.
         F_GETOWN  Value of file descriptor owner.
         other     Value other than -1.
       Otherwise, a value of -1 is returned and errno is set to  indicate  the
       error.

ERRORS
       Fcntl will fail if one or more of the following are true:

       [EBADF]        Fildes is not a valid open file descriptor.

       [EMFILE]       Cmd  is  F_DUPFD  and the maximum allowed number of file
                      descriptors are currently open.

       [EINVAL]       Cmd is F_DUPFD and arg is negative or greater  than  the
                      maximum allowable number (see getdtablesize(2)).

       [ESRCH]        Cmd  is F_SETOWN and the process ID given as argument is
                      not in use.

SEE ALSO
       close(2), execve(2), getdtablesize(2), open(2), sigvec(2)

BUGS
       The asynchronous I/O facilities of FNDELAY  and  FASYNC  are  currently
       available only for tty and socket operations.


4.2 Berkeley Distribution        May 22, 1986                         FCNTL(2)