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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]);
#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 .