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FUTIMENS(3P) POSIX Programmer's Manual FUTIMENS(3P)
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.
futimens, utimensat, utimes — set file access and modification times
#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]);
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.
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.
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.
None.
None.
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.
None.
read(3p), utime(3p)
The Base Definitions volume of POSIX.1‐2008, fcntl.h(0p),
sys_stat.h(0p), sys_time.h(0p)
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 .
IEEE/The Open Group 2013 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)
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