On 5/9/07, Dave Dykstra <dw...@drdykstra.us> wrote:
What does it really mean to preserve access times? When rsync reads
a file to copy it, it will change the access time just because it is
reading it, so the backup should then have the correct access time,
the time the backup file was created.
I tested HEAD of rsync + atimes.diff and it indeed behaves this way,
which is silly: rsync destroys the data it is told to preserve! The
atimes.test doesn't catch this because it uses a zero-length file, so
there is no read to actually hit the atime.
Some tools have an option to
reset the access time of the file they copy, but in so doing the tools
update the inode change time of the input file which is generally more
important to users than access time. It is not possible to preserve
both as a filesystem user like rsync.
It is possible on some filesystems to read a file without hitting its
atime by opening it with O_NOATIME. The same issues apply to GNU tar,
so there was an extensive discussion on the bug-tar mailing list of
how not to destroy atimes of source files (including use of
O_NOATIME):
http://lists.gnu.org/archive/html/bug-tar/2005-09/msg00035.html
Personally, I don't like access times because they're impure in the
sense that reading shouldn't write and as far as I know they don't
have any important uses. All of my computer's filesystems are mounted
noatime.
Matt
5 messages in org.samba.lists.rsyncrsync feature needed: preserve atime
