On Thu, Dec 23, 2010 at 13:07, Robert W <[email protected]> wrote: > If I use DD to back up my USB drive to a file, should I expect the checksum > of the image file created to be the same as the checksum produced by the > device (for instance, /dev/sdb)? > > I've been getting different checksums and I wanted to know if it was because > of an error writing the image file, or because of something else.
I discovered this with dd if=/dev/scd0 may be 2 years ago. dd produces an output file which is a certain size (has a one or more trailing sectors from memory). Then I burnt that image back to disc, ran dd on the new disc and got an _additional_ sector or so over and above the extra I already got the first time. So I did some research and came across wodim and readom (aptitude install wodim). wodim/readom knows the magic to not include extra sectors. At least AFAICT/remember. hth zen PS Here's my rough n hacky cheat sheet for cd/dvd commands (sorry about any line wrapping): genisoimage -J -r -f -V myvolname -o image.iso -graft-points /=symlink-farm-dir # -J, -joliet Generate Joliet directory information # -r, -rational-rock Generate rationalized Rock Ridge directory information # -R, -rock Generate Rock Ridge directory information - -r better/modern # -o FILE, -output FILE Set output file name # -path-list FILE File with list of pathnames to process # -f, -follow-links Follow symbolic links # -V ID, -volid ID Set Volume ID # -graft-points Allow to use graft points for filenames # -T, -translation-table Generate translation tables for systems that don't understand long filenames # -hide-joliet-trans-tbl Hide TRANS.TBL from Joliet tree # -joliet-long Allow Joliet file names to be 103 Unicode characters # -hide-rr-moved Rename RR_MOVED to .rr_moved in Rock Ridge tree # -hide-hfs GLOBFILE Hide HFS file # -g, -apple Add Apple ISO9660 extensions # -h, -hfs Create ISO9660/HFS hybrid # -split-output Split output into files of approx. 1GB size # -cache-inodes Cache inodes (needed to detect hard links) # RECORD ISO IMAGE, from FILE onto BLANK DISC :: sudo wodim -v -eject dev=/dev/scd0 image.iso #sudo wodim -v -eject speed=4 dev=/dev/sr0 image.iso #If the overall speed of the system is sufficient and the structure of #the filesystem is not too complex, wodim will run without creating an #image of the ISO 9660 filesystem. Simply run the pipeline: # genisoimage -R /master/tree | wodim -v fs=6m speed=2 dev=2,0 - # CREATE/ RIP ISO IMAGE data CD/DVD, from DISC to ISO FILE :: sudo readom dev=/dev/scd0 f=free-nrg.iso # To write a tar archive directly to a CD that will later contain a simple # ISO9660 filesystem with the tar archive call: tar cf - . | genisoimage -stream-media-size 333000 | wodim dev=b,t,l -dao tsize=333000s - # combine gen image/ write: genisoimage -J -r -f -V myvolname -graft-points /=symlink-farm-dir -stream-media-size 333000 | wodim dev=/dev/sr0 -dao tsize=333000s - ???check??? # Example of two alternating (actually, parallel), commands, # to optimally read in a bunch of DVDs into a local mirror: sudo readom dev=/dev/scd0 f=s.img && eject # (alternate with filename 't.img' instead of 's.img') sudo mount -o loop s.img u/ && sudo nice rsync -av u/ my-mirror/ && sudo umount u/ && sudo rm s.img # ditto for alternate t.img -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
