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

       This  page  is  part  of  release  5.10  of  the  Linux man-pages project.  A description of the project,
       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.