futimens

       #include <fcntl.h> /* Definition of AT_* constants */
       #include <sys/stat.h>

       int utimensat(int dirfd, const char *pathname,
                     const struct timespec times[2], int flags);

       int futimens(int fd, const struct timespec times[2]);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       utimensat():
           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE
       futimens():
           Since glibc 2.10:
                  _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
                  _GNU_SOURCE

DESCRIPTION
       utimensat()  and  futimens()  update  the  timestamps  of  a  file with
       nanosecond precision.  This contrasts with the historical utime(2)  and
       utimes(2),  which permit only second and microsecond precision, respec-
       tively, when setting file timestamps.

       With utimensat() the file is specified via the pathname given in  path-
       name.   With  futimens() the file whose timestamps are to be updated is
       specified via an open file descriptor, fd.

       For both calls, the new file timestamps  are  specified  in  the  array
       times:  times[0] specifies the new "last access time" (atime); times[1]
       specifies the new "last modification time" (mtime).  Each of  the  ele-
       ments  of  times specifies a time as the number of seconds and nanosec-
       onds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).   This  informa-
       tion is conveyed in a structure of the following form:

           struct timespec {
               time_t tv_sec;        /* seconds */
               long   tv_nsec;       /* nanoseconds */
           };

       Updated  file timestamps are set to the greatest value supported by the
       filesystem that is not greater than the specified time.

       If the tv_nsec field of one of the timespec structures has the  special
       value  UTIME_NOW,  then  the corresponding file timestamp is set to the
       current time.  If the tv_nsec field of one of the  timespec  structures
       has the special value UTIME_OMIT, then the corresponding file timestamp
       is left unchanged.  In both of these cases, the  value  of  the  corre-
       sponding tv_sec field is ignored.

       If times is NULL, then both timestamps are set to the current time.
       time  (i.e.,  times is not NULL, and neither tv_nsec field is UTIME_NOW
       and neither tv_nsec field is UTIME_OMIT), either condition 2 or 3 above
       must apply.

       If both tv_nsec fields are specified as UTIME_OMIT, then no file owner-
       ship or permission checks are performed, and the  file  timestamps  are
       not modified, but other error conditions may still be detected.

   utimensat() specifics
       If  pathname is relative, then by default it is interpreted relative to
       the directory referred to by the open file  descriptor,  dirfd  (rather
       than  relative to the current working directory of the calling process,
       as is done by utimes(2) for a relative pathname).  See openat(2) for an
       explanation of why this can be useful.

       If  pathname  is relative and dirfd is the special value AT_FDCWD, then
       pathname is interpreted relative to the current  working  directory  of
       the calling process (like utimes(2)).

       If pathname is absolute, then dirfd is ignored.

       The  flags  field is a bit mask that may be 0, or include the following
       constant, defined in <fcntl.h>:

       AT_SYMLINK_NOFOLLOW
              If pathname specifies a symbolic link,  then  update  the  time-
              stamps of the link, rather than the file to which it refers.

RETURN VALUE
       On  success,  utimensat()  and  futimens()  return  0.  On error, -1 is
       returned and errno is set to indicate the error.

ERRORS
       EACCES times is NULL, or both tv_nsec values are UTIME_NOW, and:
              * the effective user ID of the caller does not match  the  owner
                of  the  file,  the  caller  does not have write access to the
                file, and the caller is not privileged (Linux: does  not  have
                either the CAP_FOWNER or the CAP_DAC_OVERRIDE capability); or,
              * the file is marked immutable (see chattr(1)).

       EBADF  (futimens()) fd is not a valid file descriptor.

       EBADF  (utimensat()) pathname is a relative pathname, but dirfd is nei-
              ther AT_FDCWD nor a valid file descriptor.

       EFAULT times pointed to an invalid address; or, dirfd was AT_FDCWD, and
              pathname is NULL or an invalid address.

       EINVAL Invalid value in flags.

       EINVAL Invalid  value in one of the tv_nsec fields (value outside range
              0 to 999,999,999,  and  not  UTIME_NOW  or  UTIME_OMIT);  or  an
              invalid value in one of the tv_sec fields.

       ENOTDIR
              (utimensat()) pathname is a relative pathname, but dirfd is nei-
              ther  AT_FDCWD  nor  a file descriptor referring to a directory;
              or, one of the prefix components of pathname is not a directory.

       EPERM  The caller attempted to change one or both timestamps to a value
              other  than the current time, or to change one of the timestamps
              to the current time while leaving the other timestamp unchanged,
              (i.e.,  times  is  not NULL, neither tv_nsec field is UTIME_NOW,
              and neither tv_nsec field is UTIME_OMIT) and:
              * the caller's effective user ID does not  match  the  owner  of
                file,  and  the caller is not privileged (Linux: does not have
                the CAP_FOWNER capability); or,
              * the file is marked append-only or immutable (see chattr(1)).

       EROFS  The file is on a read-only filesystem.

       ESRCH  (utimensat()) Search permission is denied for one of the  prefix
              components of pathname.

VERSIONS
       utimensat()  was  added  to  Linux  in kernel 2.6.22; glibc support was
       added with version 2.6.

       Support for futimens() first appeared in glibc 2.6.

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

       +------------------------+---------------+---------+
       |Interface               | Attribute     | Value   |
       +------------------------+---------------+---------+
       |utimensat(), futimens() | Thread safety | MT-Safe |
       +------------------------+---------------+---------+

CONFORMING TO
       futimens() and utimensat() are specified in POSIX.1-2008.

NOTES
       utimensat() obsoletes futimesat(2).

       On Linux, timestamps cannot be changed for a file marked immutable, and
       the only change permitted for files marked append-only is  to  set  the
       timestamps  to the current time.  (This is consistent with the histori-
       cal behavior of utime(2) and utimes(2) on Linux.)

       On Linux, futimens() is a library function implemented on  top  of  the
       utimensat() system call.  To support this, the Linux utimensat() system
       call implements a nonstandard feature: if pathname is  NULL,  then  the
       call  modifies  the  timestamps  of  the  file  referred to by the file
       descriptor dirfd (which may refer to any type  of  file).   Using  this
       feature, the call futimens(fd, times) is implemented as:

         UTIME_NOW or UTIME_OMIT, then the value of the  corresponding  tv_sec
         field  should  be ignored.  Instead, the value of the tv_sec field is
         required to be 0 (or the error EINVAL results).

       * Various bugs mean that for the purposes of permission  checking,  the
         case  where  both  tv_nsec  fields  are set to UTIME_NOW isn't always
         treated the same as specifying times as NULL, and the case where  one
         tv_nsec  value is UTIME_NOW and the other is UTIME_OMIT isn't treated
         the same as specifying times as a pointer to an array  of  structures
         containing  arbitrary  time  values.   As a result, in some cases: a)
         file timestamps can be updated by a process that shouldn't have  per-
         mission  to perform updates; b) file timestamps can't be updated by a
         process that should have permission to perform updates;  and  c)  the
         wrong errno value is returned in case of an error.

       * POSIX.1  says  that  a  process that has write access to the file can
         make a call with times as NULL, or with times pointing to an array of
         structures  in  which  both tv_nsec fields are UTIME_NOW, in order to
         update both timestamps to  the  current  time.   However,  futimens()
         instead  checks whether the access mode of the file descriptor allows
         writing.

SEE ALSO
       chattr(1), futimesat(2),  openat(2),  stat(2),  utimes(2),  futimes(3),
       path_resolution(7), symlink(7)

COLOPHON
       This  page  is  part of release 4.04 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
       http://www.kernel.org/doc/man-pages/.

Linux                             2015-07-23                      UTIMENSAT(2)
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