FUTIMENS(3)                POSIX Programmer's Manual               FUTIMENS(3)



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

NAME
       futimens, utimensat, utimes -- set file access and modification times

SYNOPSIS
       #include <sys/stat.h>

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

       #include <fcntl.h>

       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 access
       mode of the open file description associated with the file descriptor
       is not O_SEARCH, the function shall check whether directory searches
       are permitted using the current permissions of the directory underlying
       the file descriptor. If the access mode is 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 successful completion, futimens() and utimensat() shall mark the
       last file status change timestamp for update, with the exception that
       if both tv__nsec fields are set to UTIME_OMIT, the file status change
       timestamp need not be marked 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 The access mode of the open file description associated with fd
              is not 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.

SEE ALSO
       read(), utime()

       The Base Definitions volume of POSIX.1-2017, <fcntl.h>, <sys_stat.h>,
       <sys_time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  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.opengroup.org/unix/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 .



IEEE/The Open Group                  2017                          FUTIMENS(3)
