On Thu, Jan 16, 2020 at 09:20:58PM -0800, William Ahern wrote:
> On Thu, Jan 16, 2020 at 01:16:47PM +0100, Otto Moerbeek wrote:
> > On Thu, Jan 16, 2020 at 11:20:10AM +0000, gritzmann wrote:
> >
> > > Hi,
> > >
> > > How do I change the birth time of a file? `touch -acm -d "1980-01-01
> > > 00:00:00" myfile` changes only the access, modify and change times.
> > >
> > > `stat myfile` returns `10 215746 -rw-r--r-- 1 me me 0 0 "Jan 1 00:00:00
> > > 1980" "Jan 1 00:00:00 1980" "Jan 16 13:00:33 2020" 16384 0 0 myfile`
> > >
> > > Thanks!
> > >
> > > Sent with ProtonMail Secure Email.
> > >
> >
> > Change time != creation time. There is no such thing as creation time
> > in unix.
>
> Not in Unix, but with UFS2 FreeBSD added birth time, which is documented
> everywhere--including in source code--as being synonymous with "creation
> time". OpenBSD added the st_birthtime field to struct stat in 2004,
>
>
> https://cvsweb.openbsd.org/src/sys/sys/stat.h?rev=1.14&content-type=text/x-cvsweb-markup
>
> https://github.com/openbsd/src/commit/cc2fc615c6e2dee87e5a3cd5a655a2ee5ef778c8
>
> but as far as I can tell it's not set anywhere in the kernel.
>
> FWIW, birth time has been adopted by ext4, ZFS, AFS, HAMMER2, and possibly
> other file systems, but only the *BSDs seem to have added st_birthtime in
> struct stat. On Linux it's stx_btime in struct statx, and as best I can tell
> Solaris requires querying the A_CRTIME (creation time?) attribute using
> getattrat. None of this is particularly relevant to OpenBSD, and I don't
> mean to advocate, but after having done the leg work I feel like I should
> commit this to an archive for posterity...
>
> > The change time (c_time in struct stat) cannot be explicitly set by
> > any API and is maintained by the kernel.
>
> As far as I can tell from the FreeBSD man page for utimes and friends, this
> is likewise true for birth time.
>
Thanks for this detailed extra info. I was vaguely aware that some
filesystem implementations have a creation time, but
- it is not in Posix and, even if *some* filesystems have it,
- there is no API to set it and no generally accepted API to get it.
-Otto
