NAME

       lseek64 - reposition 64-bit read/write file offset

SYNOPSIS

       #define _LARGEFILE64_SOURCE     /* See feature_test_macros(7) */
       #include <sys/types.h>
       #include <unistd.h>

       off64_t lseek64(int fd, off64_t offset, int whence);

DESCRIPTION

       The lseek() family of functions reposition the offset of the open file associated with the
       file descriptor fd to offset bytes relative to the start, current position, or end of  the
       file, when whence has the value SEEK_SET, SEEK_CUR, or SEEK_END, respectively.

       For more details, return value, and errors, see lseek(2).

       Four interfaces are available: lseek(), lseek64(), llseek(), and _llseek().

   lseek()
       Prototype:

           off_t lseek(int fd, off_t offset, int whence);

       The  C  library's  lseek()  wrapper function uses the type off_t.  This is a 32-bit signed
       type on 32-bit architectures, unless one compiles with

           #define _FILE_OFFSET_BITS 64

       in which case it is a 64-bit signed type.

   lseek64()
       Prototype:

           off64_t lseek64(int fd, off64_t offset, int whence);

       The lseek64() library function uses a 64-bit type even when off_t is a 32-bit  type.   Its
       prototype (and the type off64_t) is available only when one compiles with

           #define _LARGEFILE64_SOURCE

       The function lseek64() is available since glibc 2.1.

   llseek()
       Prototype:

           loff_t llseek(int fd, loff_t offset, int whence);

       The  type  loff_t  is a 64-bit signed type.  The llseek() library function is available in
       glibc and works without special defines.  However, the glibc  headers  do  not  provide  a
       prototype.   Users  should  add the above prototype, or something equivalent, to their own
       source.  When users complained about data loss caused by a  miscompilation  of  e2fsck(8),
       glibc 2.1.3 added the link-time warning

           "the `llseek´ function may be dangerous; use `lseek64´ instead."

       This makes this function unusable if one desires a warning-free compilation.

       Since   glibc  2.28,  this  function  symbol  is  no  longer  available  to  newly  linked
       applications.

   _llseek()
       On 32-bit architectures, this is the system call that is used (by the  C  library  wrapper
       functions) to implement all of the above functions.  The prototype is:

           int _llseek(int fd, off_t offset_hi, off_t offset_lo,
                       loff_t *result, int whence);

       For more details, see llseek(2).

       64-bit systems don't need an _llseek() system call.  Instead, they have an lseek(2) system
       call that supports 64-bit file offsets.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────┬───────────────┬─────────┐
       │Interface │ Attribute     │ Value   │
       ├──────────┼───────────────┼─────────┤
       │lseek64() │ Thread safety │ MT-Safe │
       └──────────┴───────────────┴─────────┘

NOTES

       lseek64() is one of the functions that was  specified  in  the  Large  File  Summit  (LFS)
       specification that was completed in 1996.  The purpose of the specification was to provide
       transitional support that allowed applications on 32-bit systems  to  access  files  whose
       size exceeds that which can be represented with a 32-bit off_t type.  As noted above, this
       symbol is exposed by header  files  if  the  _LARGEFILE64_SOURCE  feature  test  macro  is
       defined.  ALternatively, on a 32-bit system, the symbol lseek is aliased to lseek64 if the
       macro _FILE_OFFSET_BITS is defined with the value 64.

SEE ALSO

       llseek(2), lseek(2)

COLOPHON

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