All rights reserved.
%sccs.include.redist.man%
@(#)fcntl.2 6.6 (Berkeley) 06/23/90
#include <fcntl.h>res = fcntl(fd, cmd, arg) int res; int fd, cmd, arg;
DESCRIPTIONFcntl provides for control over descriptors. The argument fd is a descriptor to be operated on by cmd as follows:15 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.15 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.
15 F_SETFD Set the close-on-exec flag associated with fd to the low order bit of arg (0 or 1 as above).
15 F_GETFL Get descriptor status flags, as described below.
15 F_SETFL Set descriptor status flags.
15 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 supplying arg as negative, otherwise arg is interpreted as a process ID.
The flags for the F_GETFL and F_SETFL flags are as follows:
15 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; corresponds 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 VALUEUpon successful completion, the value returned depends on cmd as follows: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.ERRORSFcntl will fail if one or more of the following are true:15 [EBADF] Fildes is not a valid open file descriptor.
15 [EMFILE] Cmd is F_DUPFD and the maximum allowed number of file descriptors are currently open.
15 [EINVAL] Cmd is F_DUPFD and arg is negative or greater than the maximum allowable number (see getdtablesize (2)).
15 [ESRCH] Cmd is F_SETOWN and the process ID given as argument is not in use.
"SEE ALSOclose(2), execve(2), getdtablesize(2), open(2), sigvec(2)BUGSThe asynchronous I/O facilities of FNDELAY and FASYNC are currently available only for tty and socket operations.