Hi, [email protected] wrote: > > Thomas, I cited https://en.wikipedia.org/wiki/Optical_disk_image . > > ou read https://en.wikipedia.org/wiki/Disk_image .
[email protected] wrote: > When I go to that URL (as shown in my browser's URL bar) I am shown the > page accessed from the URL below, prefaced by the text "(Redirected > from Optical disk image)" Indeed i see the same (and did not notice when i wrote my previous reply). It's astounding that wikipedia shows different behavior with the same URL. If i click on the redirection note i get to https://en.wikipedia.org/w/index.php?title=Optical_disk_image&redirect=no which says not much more than "Disk Image This page was last edited on 25 July 2008, at 18:54 (UTC)." [email protected] quoted previously: > "... disk image ... written to an optical disk, disk sector by disc sector > ...". > Not directly comparable to ext4. ISO 9660 and UDF usually work with block size 2048. So they are the natural candidates for being put on optical media which show this size with their data blocks. It seems that Linux cannot handle directly ext4 after an image with default block size has been copied to an optical medium. A workaround is the use of a loop device on top of the optical drive device. I tested: dd if=/dev/zero bs=1M count=10 of=ext4_dummy.img /usr/sbin/mkfs.ext4 -t ext4 ext4_dummy.img sudo mkdir /mnt/ext sudo mount ext4_dummy.img /mnt/ext sudo chmod a+rw /mnt/ext echo hello >/mnt/ext/hello dd if=/dev/urandom bs=1M count=1 of=/mnt/ext/random_bytes ls -l /mnt/ext This shows -rw-r--r-- 1 thomas thomas 6 Jan 30 18:43 hello drwx------ 2 root root 12288 Jan 30 18:39 lost+found -rw-r--r-- 1 thomas thomas 1048576 Jan 30 18:48 random_bytes Now i put it on a DVD+RW: sudo umount /mnt/ext xorriso -as cdrecord -v dev=/dev/sr0 ext4_dummy.img After ejecting and loading the medium to kick Linux into examining its new content, i do: sudo mount /dev/sr0 /mnt/ext which fails with mount: /mnt/ext: wrong fs type, bad option, bad superblock on /dev/sr0, missing codepage or helper program, or other error. dmesg reports: EXT4-fs (sr0): bad block size 1024 But sudo losetup loop0 /dev/sr0 sudo mount /dev/loop0 /mnt/ext ls -l /mnt/ext yields -rw-r--r-- 1 thomas thomas 6 Jan 30 18:43 hello drwx------ 2 root root 12288 Jan 30 18:39 lost+found -rw-r--r-- 1 thomas thomas 1048576 Jan 30 18:48 random_bytes and in dmesg EXT4-fs (loop0): mounted filesystem c0ab3f6b-a441-452c-b97f-707842654ed4 ro with ordered data mode. Quota mode: none. Cleanup of all created file objects and DVD content: sudo umount /mnt/ext sudo losetup -d /dev/loop0 sudo rmdir /mnt/ext rm ext4_dummy.img xorriso -outdev /dev/sr0 -blank as_needed -eject all The ISO 9660 filesystem driver of Linux can deal with device block sizes different from 2048. So no loop device is necessary to mount an ISO 9660 on a storage device with block size 512 or 4192. Have a nice day :) Thomas
