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PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of
       this interface may differ (consult the corresponding Linux  manual  page  for  details  of
       Linux behavior), or the interface may not be implemented on Linux.

NAME

       futimens, utimensat, utimes — set file access and modification times

SYNOPSIS

       #include <sys/stat.h>

       int futimens(int fd, const struct timespec times[2]);
       int utimensat(int fd, const char *path, const struct timespec times[2],
           int flag);

       #include <sys/time.h>

       int utimes(const char *path, const struct timeval times[2]);

DESCRIPTION

       The  futimens() and utimensat() functions shall set the access and modification times of a
       file to the values of the times argument. The futimens() function changes the times of the
       file  associated  with the file descriptor fd.  The utimensat() function changes the times
       of the file pointed to by the path argument, relative to the directory associated with the
       file descriptor fd.  Both functions allow time specifications accurate to the nanosecond.

       For futimens() and utimensat(), the times argument is an array of two timespec structures.
       The first array member represents the date and time of last access, and the second  member
       represents the date and time of last modification. The times in the timespec structure are
       measured in seconds and nanoseconds since the Epoch. The file's relevant  timestamp  shall
       be  set  to  the  greatest value supported by the file system that is not greater than the
       specified time.

       If the tv_nsec field of a timespec structure has the special value UTIME_NOW,  the  file's
       relevant timestamp shall be set to the greatest value supported by the file system that is
       not greater than the current time. If the tv_nsec field has the special value  UTIME_OMIT,
       the file's relevant timestamp shall not be changed. In either case, the tv_sec field shall
       be ignored.

       If the times argument is a null pointer, both the access and modification timestamps shall
       be  set  to  the  greatest value supported by the file system that is not greater than the
       current time. If utimensat() is passed a relative path in the path argument, the  file  to
       be  used shall be relative to the directory associated with the file descriptor fd instead
       of the current working directory. If the file descriptor was opened without O_SEARCH,  the
       function   shall  check  whether  directory  searches  are  permitted  using  the  current
       permissions of the directory underlying the file descriptor. If the  file  descriptor  was
       opened with O_SEARCH, the function shall not perform the check.

       If  utimensat()  is  passed  the  special  value AT_FDCWD in the fd parameter, the current
       working directory shall be used.

       Only a process with the effective user ID equal to the user ID of the file, or with  write
       access  to the file, or with appropriate privileges may use futimens() or utimensat() with
       a null pointer as the times argument or with both tv_nsec fields set to the special  value
       UTIME_NOW.  Only  a process with the effective user ID equal to the user ID of the file or
       with appropriate privileges may use  futimens()  or  utimensat()  with  a  non-null  times
       argument  that  does  not have both tv_nsec fields set to UTIME_NOW and does not have both
       tv_nsec fields set to UTIME_OMIT. If  both  tv_nsec  fields  are  set  to  UTIME_OMIT,  no
       ownership or permissions check shall be performed for the file, but other error conditions
       may still be detected (including [EACCES] errors related to the path prefix).

       Values for the flag argument of utimensat() are constructed by a bitwise-inclusive  OR  of
       flags from the following list, defined in <fcntl.h>:

       AT_SYMLINK_NOFOLLOW
             If  path  names  a  symbolic  link,  then  the  access and modification times of the
             symbolic link are changed.

       Upon completion, futimens() and  utimensat()  shall  mark  the  last  file  status  change
       timestamp for update.

       The  utimes()  function  shall  be equivalent to the utimensat() function with the special
       value AT_FDCWD as the fd argument and the flag argument set to zero, except that the times
       argument  is a timeval structure rather than a timespec structure, and accuracy is only to
       the microsecond, not nanosecond, and rounding towards the nearest second may occur.

RETURN VALUE

       Upon successful completion, these functions shall return 0.   Otherwise,  these  functions
       shall  return  −1  and  set errno to indicate the error. If −1 is returned, the file times
       shall not be affected.

ERRORS

These functions shall fail if:

EACCES The times argument is a null pointer, or both tv_nsec values are UTIME_NOW, and the
effective user ID of the process does not match the owner of the file and write
access is denied.

EINVAL Either of the times argument structures specified a tv_nsec value that was neither
UTIME_NOW nor UTIME_OMIT, and was a value less than zero or greater than or equal
to 1000 million.

EINVAL A new file timestamp would be a value whose tv_sec component is not a value
supported by the file system.

EPERM The times argument is not a null pointer, does not have both tv_nsec fields set to
UTIME_NOW, does not have both tv_nsec fields set to UTIME_OMIT, the calling
process' effective user ID does not match the owner of the file, and the calling
process does not have appropriate privileges.

EROFS The file system containing the file is read-only.

The futimens() function shall fail if:

EBADF The fd argument is not a valid file descriptor.

The utimensat() function shall fail if:

EACCES fd was not opened with O_SEARCH and the permissions of the directory underlying fd
do not permit directory searches.

EBADF The path argument does not specify an absolute path and the fd argument is neither
AT_FDCWD nor a valid file descriptor open for reading or searching.

ENOTDIR
The path argument is not an absolute path and fd is a file descriptor associated
with a non-directory file.

The utimensat() and utimes() functions shall fail if:

EACCES Search permission is denied by a component of the path prefix.

ELOOP A loop exists in symbolic links encountered during resolution of the path argument.

ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.

ENOENT A component of path does not name an existing file or path is an empty string.

ENOTDIR
A component of the path prefix names an existing file that is neither a directory
nor a symbolic link to a directory, or the path argument contains at least one
non-<slash> character and ends with one or more trailing <slash> characters and the
last pathname component names an existing file that is neither a directory nor a
symbolic link to a directory.

The utimensat() and utimes() functions may fail if:

ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the
path argument.

ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic
link produced an intermediate result with a length that exceeds {PATH_MAX}.

The utimensat() function may fail if:

EINVAL The value of the flag argument is not valid.

The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       The  purpose  of  the  utimensat()  function is to set the access and modification time of
       files in directories other than the current working directory  without  exposure  to  race
       conditions.  Any  part  of  the  path  of a file could be changed in parallel to a call to
       utimes(), resulting in unspecified behavior. By opening a file descriptor for  the  target
       directory and using the utimensat() function it can be guaranteed that the changed file is
       located relative to the desired directory.

       The standard developers considered including a special case for the  permissions  required
       by  utimensat()  when  one  tv_nsec  field  is  UTIME_NOW and the other is UTIME_OMIT. One
       possibility would be to include this case in with the cases where times is a null  pointer
       or  both  fields  are  UTIME_NOW,  where  the  call  is  allowed  if the process has write
       permission for the file. However, associating write permission with an update to just  the
       last data access timestamp (which is normally updated by read()) did not seem appropriate.
       The other possibility would be to specify that this one case is allowed if the process has
       read  permission,  but  this  was  felt  to  be too great a departure from the utime() and
       utimes() functions on which utimensat() is based. If an application needs to set the  last
       data  access  timestamp to the current time for a file on which it has read permission but
       is not the owner, it can do so by opening the file, reading one or more bytes (or  reading
       a directory entry, if the file is a directory), and then closing it.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2013 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX),  The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical  Corrigendum  1  applied.)  In  the  event of any
       discrepancy between this version and the original IEEE and The Open  Group  Standard,  the
       original  IEEE  and The Open Group Standard is the referee document. The original Standard
       can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most  likely  to  have
       been  introduced  during  the conversion of the source files to man page format. To report
       such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .