NAME

fcntl - file control options

SYNOPSIS

#include <fcntl.h>

DESCRIPTION

The <fcntl.h> header  defines  the  following  requests  and
arguments  for use by the functions fcntl [see fcntl(2)] and
open [see open(2)].
   Values for cmd used by fcntl (the following values are unique):
        F_DUPFD        Duplicate file descriptor
        F_GETFD        Get file descriptor flags
        F_SETFD        Set file descriptor flags
        F_GETFL        Get file status flags
        F_SETFL        Set file status flags
        F_GETLK        Get record locking information
        F_SETLK        Set record locking information
        F_SETLKW       Set record locking information;
                       wait if blocked

   File descriptor flags used for fcntl:
        FD_CLOEXEC     Close the file descriptor upon
                       execution of an exec function [see exec(2)]

   Values for l_type used for record locking with fcntl
   (the following values are unique):
        F_RDLCK        Shared or read lock
        F_UNLCK        Unlock
        F_WRLCK        Exclusive or write lock

   The following three sets of values are bitwise distinct:
   Values for oflag used by open:
        O_CREAT        Create file if it does not exist
        O_EXCL         Exclusive use flag
        O_NOCTTY       Do not assign controlling tty
        O_TRUNC        Truncate flag

   File status flags used for open and fcntl:
        O_APPEND       Set append mode
        O_NDELAY       Non-blocking mode
        O_NONBLOCK     Non-blocking mode (POSIX)
        O_SYNC         Synchronous writes

   Mask for use with file access modes:

        O_ACCMODE      Mask for file access modes

   File access modes used for open and fcntl:
        O_RDONLY       Open for reading only
        O_RDWR         Open for reading and writing
        O_WRONLY       Open for writing only
The structure flock describes a file lock.  It includes  the
following members:
   short   l_type;     /* Type of lock */
   short   l_whence;   /* Flag for starting offset */
   off_t   l_start;    /* Relative offset in bytes */
   off_t   l_len;      /* Size; if 0 then until EOF */
   long    l_sysid;    /* Returned with F_GETLK */
   pid_t   l_pid;      /* Returned with F_GETLK */

SEE ALSO

creat(2), exec(2), fcntl(2), open(2).