#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]);
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>:
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.
The futimens() function shall fail if:
The utimensat() function shall fail if:
The utimensat() and utimes() functions shall fail if:
The utimensat() and utimes() functions may fail if:
The utimensat() function may fail if:
The following sections are informative.
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.
The Base Definitions volume of POSIX.1-2017, <fcntl.h>, <sys_stat.h>, <sys_time.h>
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