futimens.3p (10743B)
- '\" et
- .TH FUTIMENS "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH 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.
- .\"
- .SH NAME
- futimens, utimensat, utimes
- \(em set file access and modification times
- .SH SYNOPSIS
- .LP
- .nf
- #include <sys/stat.h>
- .P
- int futimens(int \fIfd\fP, const struct timespec \fItimes\fP[2]);
- .P
- #include <fcntl.h>
- .P
- int utimensat(int \fIfd\fP, const char *\fIpath\fP, const struct timespec \fItimes\fP[2],
- int \fIflag\fP);
- .P
- #include <sys/time.h>
- .P
- int utimes(const char *\fIpath\fP, const struct timeval \fItimes\fP[2]);
- .fi
- .SH DESCRIPTION
- The
- \fIfutimens\fR()
- and
- \fIutimensat\fR()
- functions shall set the access and modification times of a file
- to the values of the
- .IR times
- argument. The
- \fIfutimens\fR()
- function changes the times of the file associated with the file
- descriptor
- .IR fd .
- The
- \fIutimensat\fR()
- function changes the times of the file pointed to by the
- .IR path
- argument, relative to the directory associated with the file
- descriptor
- .IR fd .
- Both functions allow time specifications accurate to the nanosecond.
- .P
- For
- \fIfutimens\fR()
- and
- \fIutimensat\fR(),
- the
- .IR times
- argument is an array of two
- .BR 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
- .BR 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.
- .P
- If the
- .IR tv_nsec
- field of a
- .BR 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
- .IR tv_nsec
- field has the special value UTIME_OMIT, the file's relevant timestamp
- shall not be changed. In either case, the
- .IR tv_sec
- field shall be ignored.
- .P
- If the
- .IR 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
- \fIutimensat\fR()
- is passed a relative path in the
- .IR path
- argument, the file to be used shall be relative to the directory
- associated with the file descriptor
- .IR 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.
- .P
- If
- \fIutimensat\fR()
- is passed the special value AT_FDCWD in the
- .IR fd
- parameter, the current working directory shall be used.
- .P
- 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
- \fIfutimens\fR()
- or
- \fIutimensat\fR()
- with a null pointer as the
- .IR times
- argument or with both
- .IR 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
- \fIfutimens\fR()
- or
- \fIutimensat\fR()
- with a non-null
- .IR times
- argument that does not have both
- .IR tv_nsec
- fields set to UTIME_NOW and does not have both
- .IR tv_nsec
- fields set to UTIME_OMIT. If both
- .IR 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
- .BR [EACCES]
- errors related to the path prefix).
- .P
- Values for the
- .IR flag
- argument of
- \fIutimensat\fR()
- are constructed by a bitwise-inclusive OR of flags from the following
- list, defined in
- .IR <fcntl.h> :
- .IP AT_SYMLINK_NOFOLLOW 6
- .br
- If
- .IR path
- names a symbolic link, then the access and modification times
- of the symbolic link are changed.
- .br
- .P
- Upon successful completion,
- \fIfutimens\fR()
- and
- \fIutimensat\fR()
- shall mark the last file status change timestamp for update,
- with the exception that if both
- .IR tv_nsec
- fields are set to UTIME_OMIT, the file status change timestamp
- need not be marked for update.
- .P
- The
- \fIutimes\fR()
- function shall be equivalent to the
- \fIutimensat\fR()
- function with the special value AT_FDCWD as the
- .IR fd
- argument and the
- .IR flag
- argument set to zero, except that the
- .IR times
- argument is a
- .BR timeval
- structure rather than a
- .BR timespec
- structure, and accuracy is only to the microsecond, not nanosecond,
- and rounding towards the nearest second may occur.
- .SH "RETURN VALUE"
- Upon successful completion, these functions shall return 0.
- Otherwise, these functions shall return \-1 and set
- .IR errno
- to indicate the error. If \-1 is returned, the file times shall
- not be affected.
- .SH ERRORS
- These functions shall fail if:
- .TP
- .BR EACCES
- The
- .IR times
- argument is a null pointer, or both
- .IR 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.
- .TP
- .BR EINVAL
- Either of the
- .IR times
- argument structures specified a
- .IR tv_nsec
- value that was neither UTIME_NOW nor UTIME_OMIT, and was a value less
- than zero or greater than or equal to 1\|000 million.
- .TP
- .BR EINVAL
- A new file timestamp would be a value whose
- .IR tv_sec
- component is not a value supported by the file system.
- .TP
- .BR EPERM
- The
- .IR times
- argument is not a null pointer, does not have both
- .IR tv_nsec
- fields set to UTIME_NOW, does not have both
- .IR 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.
- .TP
- .BR EROFS
- The file system containing the file is read-only.
- .P
- The
- \fIfutimens\fR()
- function shall fail if:
- .TP
- .BR EBADF
- The
- .IR fd
- argument is not a valid file descriptor.
- .P
- The
- \fIutimensat\fR()
- function shall fail if:
- .TP
- .BR EACCES
- The access mode of the open file description associated with
- .IR fd
- is not O_SEARCH and the permissions of the directory underlying
- .IR fd
- do not permit directory searches.
- .TP
- .BR EBADF
- The
- .IR path
- argument does not specify an absolute path and the
- .IR fd
- argument is neither AT_FDCWD nor a valid file descriptor open
- for reading or searching.
- .TP
- .BR ENOTDIR
- The
- .IR path
- argument is not an absolute path and
- .IR fd
- is a file descriptor associated with a non-directory file.
- .P
- The
- \fIutimensat\fR()
- and
- \fIutimes\fR()
- functions shall fail if:
- .TP
- .BR EACCES
- Search permission is denied by a component of the path prefix.
- .TP
- .BR ELOOP
- A loop exists in symbolic links encountered during resolution of the
- .IR path
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- The length of a component of a pathname is longer than
- {NAME_MAX}.
- .TP
- .BR ENOENT
- A component of
- .IR path
- does not name an existing file or
- .IR path
- is an empty string.
- .TP
- .BR 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
- .IR path
- argument contains at least one non-\c
- <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.
- .P
- The
- \fIutimensat\fR()
- and
- \fIutimes\fR()
- functions may fail if:
- .TP
- .BR ELOOP
- More than
- {SYMLOOP_MAX}
- symbolic links were encountered during resolution of the
- .IR path
- argument.
- .TP
- .BR ENAMETOOLONG
- .br
- 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}.
- .P
- The
- \fIutimensat\fR()
- function may fail if:
- .TP
- .BR EINVAL
- The value of the
- .IR flag
- argument is not valid.
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- None.
- .SH RATIONALE
- The purpose of the
- \fIutimensat\fR()
- 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
- \fIutimes\fR(),
- resulting in unspecified behavior. By opening a file descriptor for
- the target directory and using the
- \fIutimensat\fR()
- function it can be guaranteed that the changed file is located relative
- to the desired directory.
- .P
- The standard developers considered including a special case for the
- permissions required by
- \fIutimensat\fR()
- when one
- .IR 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
- .IR 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
- \fIread\fR())
- 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
- \fIutime\fR()
- and
- \fIutimes\fR()
- functions on which
- \fIutimensat\fR()
- 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.
- .SH "FUTURE DIRECTIONS"
- None.
- .SH "SEE ALSO"
- .IR "\fIread\fR\^(\|)",
- .IR "\fIutime\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "\fB<fcntl.h>\fP",
- .IR "\fB<sys_stat.h>\fP",
- .IR "\fB<sys_time.h>\fP"
- .\"
- .SH 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 .
- .PP
- 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 .