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PROLOG |NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLES |APPLICATION USAGE |RATIONALE |FUTURE DIRECTIONS |SEE ALSO |COPYRIGHT | |
FUTIMENS(3P) POSIX Programmer's ManualFUTIMENS(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(intfd, const struct timespectimes[2]); #include <fcntl.h> int utimensat(intfd, const char *path, const struct timespectimes[2], intflag); #include <sys/time.h> int utimes(const char *path, const struct timevaltimes[2]);
Thefutimens() andutimensat() functions shall set the access and modification times of a file to the values of thetimes argument. Thefutimens() function changes the times of the file associated with the file descriptorfd. Theutimensat() function changes the times of the file pointed to by thepath argument, relative to the directory associated with the file descriptorfd. Both functions allow time specifications accurate to the nanosecond. Forfutimens() andutimensat(), thetimes argument is an array of twotimespecstructures. 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 thetimespec 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 thetv_nsec field of atimespecstructure 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 thetv_nsec field has the special value UTIME_OMIT, the file's relevant timestamp shall not be changed. In either case, thetv_sec field shall be ignored. If thetimes 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. Ifutimensat() is passed a relative path in thepath argument, the file to be used shall be relative to the directory associated with the file descriptorfd 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. Ifutimensat() is passed the special value AT_FDCWD in thefd 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 usefutimens() orutimensat() with a null pointer as thetimes argument or with bothtv_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 usefutimens() orutimensat() with a non-nulltimes argument that does not have bothtv_nsec fields set to UTIME_NOW and does not have bothtv_nsec fields set to UTIME_OMIT. If bothtv_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 theflag argument ofutimensat() are constructed by a bitwise-inclusive OR of flags from the following list, defined in<fcntl.h>: AT_SYMLINK_NOFOLLOW Ifpath names a symbolic link, then the access and modification times of the symbolic link are changed. Upon successful completion,futimens() andutimensat() shall mark the last file status change timestamp for update, with the exception that if bothtv_nsec fields are set to UTIME_OMIT, the file status change timestamp need not be marked for update. Theutimes() function shall be equivalent to theutimensat() function with the special value AT_FDCWD as thefd argument and theflag argument set to zero, except that thetimes argument is atimevalstructure rather than atimespecstructure, 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 seterrno to indicate the error. If -1 is returned, the file times shall not be affected.
These functions shall fail if:EACCESThetimes argument is a null pointer, or bothtv_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.EINVALEither of thetimes argument structures specified atv_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.EINVALA new file timestamp would be a value whosetv_sec component is not a value supported by the file system.EPERMThetimes argument is not a null pointer, does not have bothtv_nsec fields set to UTIME_NOW, does not have bothtv_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.EROFSThe file system containing the file is read-only. Thefutimens() function shall fail if:EBADFThefd argument is not a valid file descriptor. Theutimensat() function shall fail if:EACCESThe access mode of the open file description associated withfd is not O_SEARCH and the permissions of the directory underlyingfd do not permit directory searches.EBADFThepath argument does not specify an absolute path and thefd argument is neither AT_FDCWD nor a valid file descriptor open for reading or searching.ENOTDIR Thepath argument is not an absolute path andfd is a file descriptor associated with a non-directory file. Theutimensat() andutimes() functions shall fail if:EACCESSearch permission is denied by a component of the path prefix.ELOOPA loop exists in symbolic links encountered during resolution of thepath argument.ENAMETOOLONG The length of a component of a pathname is longer than {NAME_MAX}.ENOENTA component ofpath does not name an existing file orpath 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 thepath 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. Theutimensat() andutimes() functions may fail if:ELOOPMore than {SYMLOOP_MAX} symbolic links were encountered during resolution of thepath 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}. Theutimensat() function may fail if:EINVALThe value of theflag argument is not valid.The following sections are informative.None.
None.
The purpose of theutimensat() 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 toutimes(), resulting in unspecified behavior. By opening a file descriptor for the target directory and using theutimensat() 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 byutimensat() when onetv_nsec field is UTIME_NOW and the other is UTIME_OMIT. One possibility would be to include this case in with the cases wheretimes 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 byread()) 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 theutime() andutimes() functions on whichutimensat() 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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017FUTIMENS(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)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |