1FCNTL(2)                      System Calls Manual                     FCNTL(2)
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NAME

6       fcntl - file control
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SYNOPSIS

9       #include <fcntl.h>
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11       res = fcntl(fd, cmd, arg)
12       int res;
13       int fd, cmd, arg;
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DESCRIPTION

16       Fcntl  provides  for  control  over  descriptors.  The argument fd is a
17       descriptor to be operated on by cmd as follows:
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19       F_DUPFD        Return a new descriptor as follows:
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21                      Lowest numbered available  descriptor  greater  than  or
22                      equal to arg.
23
24                      Same object references as the original descriptor.
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26                      New  descriptor  shares  the  same  file  pointer if the
27                      object was a file.
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29                      Same access mode (read, write or read/write).
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31                      Same file status  flags  (i.e.,  both  file  descriptors
32                      share the same file status flags).
33
34                      The  close-on-exec  flag  associated  with  the new file
35                      descriptor is set to remain open across execv(2)  system
36                      calls.
37
38       F_GETFD        Get  the  close-on-exec  flag  associated  with the file
39                      descriptor fd.  If the low-order bit is 0, the file will
40                      remain  open  across  exec,  otherwise  the file will be
41                      closed upon execution of exec.
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43       F_SETFD        Set the close-on-exec flag associated with fd to the low
44                      order bit of arg (0 or 1 as above).
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46       F_GETFL        Get descriptor status flags, as described below.
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48       F_SETFL        Set descriptor status flags.
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50       F_GETOWN       Get  the process ID or process group currently receiving
51                      SIGIO and SIGURG signals; process groups are returned as
52                      negative values.
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54       F_SETOWN       Set  the  process  or process group to receive SIGIO and
55                      SIGURG signals; process groups are specified by  supply‐
56                      ing  arg  as negative, otherwise arg is interpreted as a
57                      process ID.
58
59       The flags for the F_GETFL and F_SETFL flags are as follows:
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61       O_NONBLOCK     Non-blocking I/O; if no data  is  available  to  a  read
62                      call,  or  if  a  write  operation would block, the call
63                      returns -1 with the error EWOULDBLOCK.
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65       O_APPEND       Force each write to append at the end  of  file;  corre‐
66                      sponds to the O_APPEND flag of open(2).
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68       O_ASYNC        Enable  the SIGIO signal to be sent to the process group
69                      when I/O is possible, e.g., upon availability of data to
70                      be read.
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RETURN VALUE

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

84       Fcntl will fail if one or more of the following are true:
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86       [EBADF]        Fildes is not a valid open file descriptor.
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88       [EMFILE]       Cmd  is  F_DUPFD  and the maximum allowed number of file
89                      descriptors are currently open.
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91       [EINVAL]       Cmd is F_DUPFD and arg is negative or greater  than  the
92                      maximum allowable number (see getdtablesize(2)).
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94       [ESRCH]        Cmd  is F_SETOWN and the process ID given as argument is
95                      not in use.
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SEE ALSO

98       close(2), execve(2), getdtablesize(2), open(2), sigvec(2)
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BUGS

101       The asynchronous I/O facilities of O_NONBLOCK and O_ASYNC are currently
102       available only for tty and socket operations.
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1064.2 Berkeley Distribution        Nov 30, 1994                         FCNTL(2)