futimens(3p) — Linux manual page

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

PROLOG         top

       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         top

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

SYNOPSIS         top

       #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         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       read(3p), utime(3p)

       The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
       sys_stat.h(0p), sys_time.h(0p)

COPYRIGHT         top

       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(3P)

Pages that refer to this page: fcntl.h(0p)sys_stat.h(0p)sys_time.h(0p)utime.h(0p)touch(1p)time(3p)utime(3p)utimensat(3p)