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.\"     @(#)utimes.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: head/lib/libc/sys/utimensat.2 294234 2016-01-17 21:14:27Z jilles $
.\"
.Dd January 17, 2016
.Dt UTIMENSAT 2
.Os
.Sh NAME
.Nm futimens ,
.Nm utimensat
.Nd set file access and modification times
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/stat.h
.Ft int
.Fn futimens "int fd" "const struct timespec times[2]"
.Ft int
.Fo utimensat
.Fa "int fd"
.Fa "const char *path"
.Fa "const struct timespec times[2]"
.Fa "int flag"
.Fc
.Sh DESCRIPTION
The access and modification times of the file named by
.Fa path
or referenced by
.Fa fd
are changed as specified by the argument
.Fa times .
The inode-change-time of the file is set to the current time.
.Pp
If
.Fa path
specifies a relative path,
it is relative to the current working directory if
.Fa fd
is
.Dv AT_FDCWD
and otherwise relative to the directory associated with the file descriptor
.Fa fd .
.Pp
The
.Va tv_nsec
field of a
.Vt timespec
structure
can be set to the special value
.Dv UTIME_NOW
to set the current time, or to
.Dv UTIME_OMIT
to leave the time unchanged.
In either case, the
.Va tv_sec
field is ignored.
.Pp
If
.Fa times
is
.No non- Ns Dv NULL ,
it is assumed to point to an array of two timespec structures.
The access time is set to the value of the first element, and the
modification time is set to the value of the second element.
For file systems that support file birth (creation) times (such as
.Dv UFS2 ) ,
the birth time will be set to the value of the second element
if the second element is older than the currently set birth time.
To set both a birth time and a modification time,
two calls are required; the first to set the birth time
and the second to set the (presumably newer) modification time.
Ideally a new system call will be added that allows the setting
of all three times at once.
If
.Fa times
is
.Dv NULL ,
this is equivalent to passing
a pointer to an array of two timespec structures
with both
.Va tv_nsec
fields set to
.Dv UTIME_NOW .
.Pp
If both
.Va tv_nsec
fields are
.Dv UTIME_OMIT ,
the timestamps remain unchanged and
no permissions are needed for the file itself,
although search permissions may be required for the path prefix.
The call may or may not succeed if the named file does not exist.
.Pp
If both
.Va tv_nsec
fields are
.Dv UTIME_NOW ,
the caller must be the owner of the file, have permission to
write the file, or be the super-user.
.Pp
For all other values of the timestamps,
the caller must be the owner of the file or be the super-user.
.Pp
The values for the
.Fa flag
argument of the
.Fn utimensat
system call
are constructed by a bitwise-inclusive OR of flags from the following list,
defined in
.In fcntl.h :
.Bl -tag -width indent
.It Dv AT_SYMLINK_NOFOLLOW
If
.Fa path
names a symbolic link, the symbolic link's times are changed.
By default,
.Fn utimensat
changes the times of the file referenced by the symbolic link.
.El
.Sh RETURN VALUES
.Rv -std
.Sh COMPATIBILITY
If the running kernel does not support this system call,
a wrapper emulates it using
.Xr fstatat 2 ,
.Xr futimesat 2
and
.Xr lutimes 2 .
As a result, timestamps will be rounded down to the nearest microsecond,
.Dv UTIME_OMIT
is not atomic and
.Dv AT_SYMLINK_NOFOLLOW
is not available with a path relative to a file descriptor.
.Sh ERRORS
These system calls will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
The
.Fa times
argument is
.Dv NULL ,
or both
.Va tv_nsec
values are
.Dv UTIME_NOW ,
and the effective user ID of the process does not
match the owner of the file, and is not the super-user, and write
access is denied.
.It Bq Er EFAULT
The
.Fa times
argument
points outside the process's allocated address space.
.It Bq Er EINVAL
The
.Va tv_nsec
component of at least one of the values specified by the
.Fa times
argument has a value less than 0 or greater than 999999999 and is not equal to
.Dv UTIME_NOW
or
.Dv UTIME_OMIT .
.It Bq Er EIO
An I/O error occurred while reading or writing the affected inode.
.It Bq Er EPERM
The
.Fa times
argument is not
.Dv NULL
nor are both
.Va tv_nsec
values
.Dv UTIME_NOW ,
nor are both
.Va tv_nsec
values
.Dv UTIME_OMIT
and the calling process's effective user ID
does not match the owner of the file and is not the super-user.
.It Bq Er EPERM
The named file has its immutable or append-only flag set, see the
.Xr chflags 2
manual page for more information.
.It Bq Er EROFS
The file system containing the file is mounted read-only.
.El
.Pp
The
.Fn futimens
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument
does not refer to a valid descriptor.
.El
.Pp
The
.Fn utimensat
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor.
.It Bq Er EFAULT
The
.Fa path
argument
points outside the process's allocated address space.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters, or an entire path name exceeded
.Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.It Bq Er ENOTSUP
The running kernel does not support this system call and
.Dv AT_SYMLINK_NOFOLLOW
is used with a path relative to a file descriptor.
.El
.Sh SEE ALSO
.Xr chflags 2 ,
.Xr stat 2 ,
.Xr symlink 2 ,
.Xr utimes 2 ,
.Xr utime 3 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn futimens
and
.Fn utimensat
system calls are expected to conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn futimens
and
.Fn utimensat
system calls appeared in
.Fx 10.3 .