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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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]);
#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]);
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.
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 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.
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.1‐2017, 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 1003.1-2017, 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)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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