Date: Wed, 28 Sep 2016 01:12:23 +1000 (EST) From: Ian Smith <smithi@nimnet.asn.au> To: David Christensen <dpchrist@holgerdanske.com> Cc: freebsd-questions@freebsd.org Subject: FreeBSD-10.3-RELEASE-i386-memstick.img installer changes contents of USB flash drive? Message-ID: <20160927032651.T6806@sola.nimnet.asn.au> In-Reply-To: <mailman.125.1474891202.61703.freebsd-questions@freebsd.org> References: <mailman.125.1474891202.61703.freebsd-questions@freebsd.org>
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In freebsd-questions Digest, Vol 643, Issue 1, Message: 5 On Sun, 25 Sep 2016 20:36:15 -0700 David Christensen <dpchrist@holgerdanske.com> wrote: > Using Debian GNU/Linux 7.11, I downloaded > FreeBSD-10.3-RELEASE-i386-memstick.img and burned it to a USB flash drive: > > # time dd if=FreeBSD-10.3-RELEASE-i386-memstick.img of=/dev/sdc > bs=1M conv=sync; sync > 659+1 records in > 660+0 records out > 692060160 bytes (692 MB) copied, 141.567 s, 4.9 MB/s > > real 2m21.571s > user 0m0.004s > sys 0m1.696s > > > If I compute the checksum immediately after burning, it matches the > published checksum: > > # time dd if=/dev/sdc count=1350917 | sha256sum -b > ab104a30627754bb8d39eeff3c5c5a4a15537d32c749e2b9841b34cb08e17eb0 *- > 1350917+0 records in > 1350917+0 records out > 691669504 bytes (692 MB) copied, 43.252 s, 16.0 MB/s > > real 0m43.257s > user 0m7.236s > sys 0m3.496s > > # grep > ab104a30627754bb8d39eeff3c5c5a4a15537d32c749e2b9841b34cb08e17eb0 > CHECKSUM.SHA256-FreeBSD-10.3-RELEASE-i386 > SHA256 (FreeBSD-10.3-RELEASE-i386-memstick.img) = > ab104a30627754bb8d39eeff3c5c5a4a15537d32c749e2b9841b34cb08e17eb0 > > > But after using the USB flash drive to install FreeBSD, the checksum has > changed: > > # dd if=/dev/sdc count=1350917 | sha256sum -b > 1350917+0 records in > 1350917+0 records out > bd159b85486322febe992226bbec9c86d96d70dd1e5a8b7c6f0bb9d29eb50df3 *- > 691669504 bytes (692 MB) copied, 42.989 s, 16.1 MB/s > > > Therefore, the FreeBSD-10.3-RELEASE-i386-memstick.img installer has > changed the contents of the USB flash drive. Just checking .. did you only access the stick by reading with dd? That is, that you never mounted it for a look around - requiring mounting it -o ro, or at least noatime, to avoid directory atime updating on reads? > Why? Where? i.e, where on the memstick does it first differ from its memstick.img file? You can use cmp(1) to locate the first difference, reduce the byte count to sectors (N) then perhaps: dd if=memstick.img skip=$((N-1)) count=8 | hd > image.4k.hd dd if=/dev/da$whatever skip=$((N-1)) count=8 | hd > stick.4k.hd diff -u image.4k.hd stick.4k.hd I just checked my FreeBSD-10.3-RELEASE-amd64-memstick.img vs the stick I'd dd'd it to, to find amongst others in the first lot of differences "/media" which is a local directory I'd mounted it on at some stage .. this was just past 8k into the image, so I didn't need to skip further. If anything but atimes are modified, that would be very interesting .. I thought installation didn't write anything to the source stick at all. Like Perry H, I'd like to add a small partition to memsticks to write stuff to, at least from 'live CD' mode, if not a shell from installer. cheers, Ian
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