FUTIMENS(3P) POSIX Programmer's Manual FUTIMENS(3P)
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 modi-
fication times of a file to the values of the times argument. The futi-
mens() 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 time-
stamp 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 modifica-
tion 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 parame-
ter, 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 bit-
wise-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 argu-
ment set to zero, except that the times argument is a timeval structure
rather than a timespec structure, and accuracy is only to the microsec-
ond, 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 resolu-
tion 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 modi-
fication 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 permis-
sion 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 permis-
sion, 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.1-2008, <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, 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 Electri-
cal 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.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FUTIMENS(3P)
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