I think kernel already generates some faked up UUIDs, i.e. i think there is something for like FAT and DOS partition table, either fs uuid, or like partition table uuid, partition uuid, partition type uuid, some such.
They are "shorter" than normal, and less unique, but at least something. Should we request squashfs userspace tooling and kernel to start having a UUID in the squashfs? We do use squashfs a lot, all the snaps and all the installer media. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1824407 Title: remount of multilower moved pivoted-root overlayfs root, results in I/O errors on some modified files Status in linux package in Ubuntu: Confirmed Status in linux-hwe package in Ubuntu: Invalid Status in linux-hwe source package in Bionic: Confirmed Bug description: 1) Download focal subiquity pending image, or eoan release image 2) boot, and press ESC and edit boot command line (F6 in bios, e in UEFI) 3) After --- insert the following options break=top debug init=/bin/bash 4) Continue boot (Enter in BIOS, ctrl+x in UEFI) 5) in the initramfs execute: rm /scripts/casper-bottom/25adduser exit 6) you will be dropped into pivoted root filesystem, before systemd is execed as pid one 7) /run/initramfs/ will contain a debug log, showing how everything was mounted. Ie. cdrom mounted, squashfs losetup from there, then multilower overlay setup from them, moved to /root, and then pivot-root to /root done to finally end up as /. Underlying layers are moved into /cow for your convenience. 8) At this point modifying zero-byte length files, that exist in the lowest layer, but not the middle one, in certain ways, will results in them to be corrupted, after / is remounted. 9) Corruption examples (On both focal & eoan) cat /etc/.pwd.lock systemd-sysusers cat /etc/.pwd.lock mount -o remount / cat /etc/.pwd.lock overlayfs: invalid origin (etc/.pwd.lock, ftype=8000, origin ftype=4000) cat: /etc/.pwd.lock: Input/output error (Only on eoan) cat /etc/machine-id systemd-machine-id-setup cat /etc/machine-id mount -o remount / cat /etc/machine-id overlayfs: invalid origin (etc/machine-id, ftype=8000, origin ftype=4000) cat: /etc/machine-id: Input/output error Lots of things break once machine-id and .pwd.lock are corrupted. I.e. unable to dhcp, connect to dbus, add/remove/change users or groups, etc. We were unable to recreate the issue outside of booting things with casper. Ie. statically on a regular host machine without pivot-root. But hopefully booting to a quite state with nothing running is sufficient to reproduce this. Instead of booting with `bebroken init=/bin/bash` you can boot with `bebroken systemd.mask=systemd-remount-fs.service` this will complete the boot, with /etc/machine-id & .pwd.lock modified, meaning that remount of / will cause IO errors on those files. Currently, we are shipping two hacks in casper's 25adduser script to "rm" the offending files, and create them again on the upper rw layer. They then survive remount without i/o errors. However, we'd rather not ship those hacks, and have kernel overlay fixed to work correctly with multi-lower-dir and not corrupt files upon remounting /. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1824407/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp