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    Command:

    utimensat

    
    
    

    SYNOPSIS

           #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-
           To make any change other than setting both timestamps  to  the  current
           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  times-
                  tamps 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
    
           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.
    
    
    

    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:
    
               utimensat(fd, NULL, times, 0);
    
    
    

    BUGS

           Several bugs afflict  utimensat()  and  futimens()  on  kernels  before
           2.6.26.   These  bugs are either nonconformances with the POSIX.1 draft
           specification or inconsistencies with historical Linux behavior.
    
             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)
    
    
    

    Linux 2014-01-24 UTIMENSAT(2)

    
    
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