OPEN(2)                          System calls                          OPEN(2)

NAME
       open, creat - <?><?><?>/<?><?><?><?><?><?><?>

SYNOPSIS <?><?>
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <fcntl.h>

       int open(const char *pathname, int flags);
       int open(const char *pathname, int flags, mode_t mode)
       int creat(const char *pathname, mode_t mode);

<?><?> (DESCRIPTION)
       open()
       <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>
       read  ,  write <?> I/O <?><?><?><?><?><?><?><?><?><?><?> open()
       <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>
       fork (2) <?><?><?><?><?><?><?><?><?><?>
       <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>
       fcntl(2) <?><?><?><?><?><?><?><?><?><?><?><?><?><?>

       <?><?> flags <?><?><?> O_RDONLY, O_WRONLY <?> O_RDWR (<?><?> <?><?>
       <?><?> <?><?> , <?><?> <?> <?><?> <?><?> <?><?><?>) <?> <?><?><?>
       <?><?> <?> <?><?> <?><?><?><?> <?><?> -or <?><?> <?><?><?>:

       O_CREAT
              <?><?><?> <?><?><?> <?> <?><?> <?><?> <?> <?><?>.  <?> <?><?>
              <?> <?><?> (<?><?><?>ID) <?> <?><?> <?> <?> <?><?> <?> <?><?>
              <?><?><?> <?> ID.  <?><?> <?><?> <?><?> <?><?> <?> <?> <?><?>
              <?> <?> <?><?> <?> <?><?> <?><?> <?> ID <?><?> <?><?> <?><?> <?>
              <?><?> ID (<?> <?><?> <?><?><?><?> <?><?> ,<?><?><?><?> <?>
              <?><?><?><?> <?> <?><?>, <?><?>,<?> mount(8) <?> <?><?> <?> ext2
              <?><?><?><?> <?> <?><?><?><?> bsdgroups <?> sysvgroups )

       O_EXCL <?><?> O_CREAT, <?><?> <?><?> , <?> <?><?> <?><?> <?><?> , <?>
              open <?><?> , <?><?> <?><?> . <?><?> <?><?> <?><?><?><?> ,
              <?><?> <?> <?><?> <?><?><?><?> <?> <?><?> <?><?> <?><?>.  O_EXCL
              is broken on NFS file systems, programs which rely on it for
              performing locking tasks will contain a race condition.  The
              solution for performing atomic file locking using a lockfile is
              to create a unique file on the same fs (e.g., incorporating
              hostname and pid), use link(2) to make a link to the lockfile.
              If link() returns 0, the lock is successful.  Otherwise, use
              stat(2) on the unique file to check if its link count has
              increased to 2, in which case the lock is also successful.

       O_NOCTTY
              <?><?> pathname <?><?> <?><?> <?><?><?><?> -- <?><?> tty(4) --
              <?><?> <?><?> <?><?> <?><?><?><?> ,<?><?> <?><?> <?> <?><?>
              <?><?> <?><?> <?> <?><?> <?><?>.

       O_TRUNC
              <?><?> <?><?> <?><?> <?><?> , <?><?> <?><?> <?><?> <?><?>
              ,<?><?> <?><?> <?><?> <?><?>(<?> <?><?> <?> <?> O_RDWR <?>
              O_WRONLY <?><?> <?><?> <?>) , <?><?> <?><?> <?> <?><?> <?><?>
              <?> <?> , <?><?> <?><?> <?> <?><?> <?><?>.<?> <?><?> <?> <?><?>
              FIFO <?> <?><?><?><?> <?><?> , O_TRUNC <?><?> <?> <?><?>.
              <?><?> O_TRUNC <?> <?><?> <?> <?> <?><?> <?><?> <?> (<?> <?><?>
              Linux <?><?> <?> , <?><?> <?> <?> <?><?> , <?><?> <?> <?><?>
              <?><?> <?> <?><?> <?><?> <?><?>)

       O_APPEND
              <?><?> <?> <?><?> <?><?> <?><?> . <?> <?> <?><?> , <?><?> <?><?>
              <?><?> <?> <?> <?> <?><?> <?> <?><?> .  as if with lseek.
              O_APPEND may lead to corrupted files on NFS file systems if more
              than one process appends data to a file at once.  This is
              because NFS does not support appending to a file, so the client
              kernel has to simulate it, which can't be done without a race
              condition.

       O_NONBLOCK <?> O_NDELAY
              <?><?>(open) <?><?> <?><?> <?> <?><?>(non-blocking) <?><?>
              <?><?> . <?><?> <?><?> <?> <?><?> <?><?> , <?> <?><?> <?><?>
              <?><?> <?> <?><?><?><?><?> <?><?> <?><?> <?><?> , <?><?> <?>
              <?><?> <?><?> <?><?> . <?> <?><?> <?> <?><?> FIFO (<?><?><?><?>)
              <?> <?><?> , <?><?> fifo(4).  <?><?> <?><?> <?> <?><?> FIFO <?>
              <?><?> <?><?> <?><?> .

       O_SYNC <?><?> <?><?> <?><?> I/O <?> <?><?> . <?><?> <?><?>
              <?><?><?><?><?> <?> <?><?> <?> write <?><?> <?> <?><?> <?>
              <?><?> <?><?> , <?><?> <?><?> <?> <?><?> <?><?> <?><?> <?> .
              <?><?> , <?><?> RESTRICTIONS.

       O_NOFOLLOW
              <?><?> pathname <?> <?><?> <?><?> <?><?> , <?> <?><?> <?><?> .
              <?><?> FreeBSD <?> <?><?> , <?> 2.1.126 <?><?> <?><?> <?> <?><?>
              <?> Linux <?><?> .  <?> glibc2.0.100 <?> <?><?> , <?><?><?><?>
              <?> <?><?> <?> <?><?> <?><?> <?> <?><?>;
                kernel 2.1.126 <?><?> <?> <?><?> <?><?> <?><?>.

       O_DIRECTORY
              <?><?> pathname <?><?> <?><?> , <?><?> <?> <?><?> . <?><?>
              <?><?> <?> Linux <?><?> <?> , <?> kernel 2.1.126 <?> <?><?> ,
              <?><?> <?><?> <?> <?><?> FIFO <?> <?><?><?><?> <?> <?> denial-
              of-service <?><?> , <?><?> <?><?><?> <?> <?><?> opendir <?><?>
              <?><?>.

       O_LARGEFILE
              <?> 32<?> <?><?> <?> <?><?> <?> <?><?><?><?> , <?><?> <?><?>
              <?><?> <?> 31<?> <?> <?><?> <?><?> <?> <?><?> <?> <?> <?><?> .

       <?> <?><?> <?><?> <?> , <?><?> <?><?> <?><?> <?><?> <?><?> fcntl <?>
       <?><?> .

       <?> <?><?><?> <?> <?><?> <?> , <?><?> mode <?><?> <?><?> <?> <?><?>
       <?><?><?> . <?> <?><?> <?> <?> <?> umask <?><?> . <?><?> <?><?> <?><?>
       <?><?> <?> <?><?><?> <?> (mode & ~umask).  <?><?> <?><?> <?> <?> <?><?>
       <?> <?><?> <?> <?> <?><?><?> <?> <?><?> <?>; open <?><?> <?><?> <?><?>
       <?><?> <?><?> <?><?> , <?> <?> <?> <?><?> <?><?> <?> <?><?> <?><?>
       <?><?><?>.

       <?><?> <?> <?><?> mode <?> <?><?> <?><?>:

       S_IRWXU
              00700 <?><?> <?><?> <?> <?><?> <?> , <?> <?> <?><?> <?><?>

       S_IRUSR (S_IREAD)
              00400 <?><?> <?><?> <?> <?><?> <?> <?><?>

       S_IWUSR (S_IWRITE)
              00200 <?><?> <?><?> <?> <?><?> <?> <?><?>

       S_IXUSR (S_IEXEC)
              00100 <?><?> <?><?> <?> <?><?> <?><?> <?><?>

       S_IRWXG
              00070 <?><?> <?><?> <?><?> <?> <?><?> <?> , <?> <?> <?><?>
              <?><?>

       S_IRGRP
              00040 <?><?> <?><?> <?><?> <?> <?><?> <?> <?><?>

       S_IWGRP
              00020 <?><?> <?><?> <?><?> <?> <?><?> <?> <?><?>

       S_IXGRP
              00010 <?><?> <?><?> <?><?> <?> <?><?> <?><?> <?><?>

       S_IRWXO
              00007 <?><?> <?><?> <?><?><?> <?> , <?> <?> <?><?> <?><?>

       S_IROTH
              00004 <?><?> <?><?> <?><?><?> <?> <?><?>

       S_IWOTH
              00002 <?><?> <?><?> <?><?><?> <?> <?><?>

       S_IXOTH
              00001 <?><?> <?><?> <?><?><?> <?><?> <?><?>

       mode <?><?> <?> <?> flags <?> <?><?> O_CREAT <?> <?> <?><?> , <?><?>
       <?> <?><?>.

       creat <?><?> <?> open <?> <?><?> flags <?><?> O_CREAT|O_WRONLY|O_TRUNC.

RETURN VALUE <?><?><?>
       open <?> creat <?> <?><?> <?><?> <?><?> <?><?><?><?><?> (<?><?> <?>
       <?><?> <?><?> <?><?> -1 ,<?><?> errno <?><?> <?><?> <?><?>).  <?><?>
       open <?><?> <?><?> <?><?> <?><?> <?><?> , <?><?> creat
       <?><?><?><?>,<?><?><?> mknod(2) <?><?><?>.

       On NFS file systems with UID mapping enabled, open may return a file
       descriptor but e.g. read(2) requests are denied with EACCES.  This is
       because the client performs open by checking the permissions, but UID
       mapping is performed by the server upon read and write requests.

       <?> <?><?> <?> <?> <?><?> <?> , <?> <?> atime(<?><?><?><?><?><?>),
       ctime(<?><?><?><?>), mtime(<?><?><?><?>) <?> <?> <?><?> <?> <?><?>
       <?><?> , <?><?> <?><?> <?>atime , ctime <?> <?> <?><?> <?><?> .
       <?><?><?> , <?><?> <?><?> <?> <?> O_TRUNC <?><?> <?><?> <?> ,<?><?>
       ctime , mtime <?> <?> <?> <?><?> <?> <?><?> <?><?>.


ERRORS <?><?><?><?>
       EEXIST <?><?> O_CREAT and O_EXCL <?> <?><?>,<?><?><?><?>( pathname
              )<?><?><?><?>.

       EISDIR <?><?> ( pathname ) <?> <?><?> <?><?> , <?> <?> <?><?> <?> <?>
              <?><?>.

       EACCES
               <?><?> <?><?> <?> <?><?> (<?><?><?><?><?>) , <?> <?><?> (
              pathname )<?> <?> <?> <?><?> <?><?><?> <?><?> (<?><?>
              <?><?><?><?><?>) , <?><?> <?><?> <?> <?><?><?> <?> <?>
              <?><?><?><?> <?> <?> <?><?> <?> <?><?><?>.

       ENAMETOOLONG
              <?><?> ( pathname ) <?> <?> <?>

       ENOENT <?><?> ( pathname ) <?><?><?> <?><?> <?> <?><?> <?><?> <?>
              <?><?> <?><?>.

       ENOTDIR
              pathname <?><?> <?><?> <?><?><?>

       ENXIO  <?><?> O_NONBLOCK | O_WRONLY, <?><?> <?> <?><?> <?> FIFO ,
              <?><?> <?><?> <?> <?><?> <?><?> <?> <?><?> , <?><?> , <?><?>
              <?><?> <?><?> <?><?> <?><?> <?> <?><?> <?> <?><?> <?><?><?>

       ENODEV <?><?> ( pathname ) <?><?> <?> <?><?> <?><?> <?><?> <?><?> , <?>
              <?><?> <?> <?><?> <?> <?><?><?>.  (<?><?> linux kernel <?>
              <?><?>bug - ENXIO <?><?> <?> <?> <?><?> .)

       EROFS  <?><?> ( pathname )
              <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>

       ETXTBSY
              <?><?> ( pathname )
              <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>

       EFAULT pathname <?><?><?><?><?><?><?><?><?><?><?><?><?>.

       ELOOP  <?> <?><?> pathname <?> , <?><?> <?><?> <?><?><?><?> <?><?>
              <?><?> O_NOFOLLOW <?><?> pathname <?> <?><?> <?><?><?><?>

       ENOSPC pathname <?><?><?><?><?>,<?><?><?><?><?><?><?><?><?><?><?>
              pathname <?><?><?>

       ENOMEM <?> <?><?> <?> <?><?><?><?><?>(kernel memory) <?><?>

       EMFILE <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>

       ENFILE <?><?><?><?><?><?><?><?><?><?><?><?><?><?><?><?>

CONFORMING TO
       SVr4, SVID, POSIX, X/OPEN, BSD 4.3 The O_NOFOLLOW and O_DIRECTORY flags
       are Linux-specific.  One may have to define the _GNU_SOURCE macro to
       get their definitions.

RESTRICTIONS <?><?><?>
       There are many infelicities in the protocol underlying NFS, affecting
       amongst others O_SYNC and O_NDELAY.

       POSIX provides for three different variants of synchronised I/O,
       corresponding to the flags O_SYNC, O_DSYNC and O_RSYNC.  Currently
       (2.1.130) these are all synonymous under Linux.

SEE ALSO <?><?>
       read(2), write(2), fcntl(2), close(2), link(2), mknod(2), mount(2),
       stat(2), umask(2), unlink(2), socket(2), fopen(3), fifo(4)


[<?><?><?><?><?><?>]
       Daniel <badlong@163.com>

[<?><?><?><?><?><?><?>]
       2002/01/10

<?><?><?>linux<?><?>man<?><?><?><?><?><?><?><?>:
       http://cmpp.linuxforum.net

<?>
       <?><?><?><?><?><?><?><?><?> man <?><?><?><?><?><?><?><?>
       <?><?> man <?><?><?><?><?><?>https://github.com/man-pages-zh/manpages-
       zh

Linux                             1999-06-03                           OPEN(2)