Fedora 26 failed to boot overlay

[c0b]

with unmodified Fedora liveiso image, what I usually do is to append a special parameter rd.break=pre-pivot on grub command line, then the dracut initramfs image will break into a debug shell before pivot, then I can manually type in a few key commands from the 01-liveoverlayfs.sh like modprobe ... overlay, and mkdir /run/{sysroot,upper,work} and the mount, quit the shell and dracut continues to boot up into a desktop with / mounted on top of overlayfs;
this works for the past 25, 24, ... a few prior versions, but stops working on Fedora 26

it failed at this line

https://github.com/probonopd/SystemImageKit/blob/b44abfa/boot/iso/additional-initramfs/dracut-overlayfs-support/usr/lib/dracut/hooks/pre-pivot/01-liveoverlayfs.sh#L30

mount /run/initramfs/squashfs/LiveOS/rootfs.img /run/sysroot

error is:

mount: /dev/loop2 is already mounted or /run/sysroot busy

[probonopd]

Thanks @c0b for analyzing this, do you know how to fix it?

[c0b]

I think the root cause is the program mount in Fedora 26 must be a new version becomes clever, it detects in the case if need to setup a loop device, it checks if the file is already setup on some existing loop device, which is true at the moment of pre-pivot, because some where in the dracut bootup scripts has already setup the /LiveOS/rootfs.img from the squashfs file at /dev/loop2, and device-mapper is using the loop device in an exclusive way, this is my theory why mount failed and says /dev/loop2 already in-use; there might be two solutions:

1. dmsetup remove_all before the rootfs.img mount, since the overlay don't use any device-mapper at all, it may be safe to get rid of all device-mapper, but I remember for F25/24 it failed at some later step of dracut not remember details;

2. manually setup another duplicate loop device for the rootfs.img, for the older version of mount it didn't check existing loop device and always setup a new loop device:

   # losetup -f /run/initramfs/squashfs/LiveOS/rootfs.img
   .... some output here, suppose it find next free loop device is /dev/loop4
   # mount -v -o ro /dev/loop4 /run/sysroot
   .... the verbose flag isn't really necessary, but I'd always like to be verbose

I am using the 2nd solution as workaround, it indeed works; I also need enforcing=0 to avoid some stupid selinux layer, after boot into overlay based Live desktop, it's safe to run dmsetup remove_all and losetup -d /dev/loop* (this one only mark all loop devices to be lazy delete, since device-mapper removed, some loop devices in-use by device-mapper will be deleted immediately and others used by overlay will continue serve, till system shutdown...)

[c0b]

@probonopd as the workaround is figured out does work for fedora 26, do you want an update of this 01-liveoverlayfs.sh#L30 file? as you mentioned in dracutdevs/dracut#104 I am the original author derek exposed the fedora overlay problem at https://lists.fedoraproject.org/pipermail/users/2015-July/463627.html

[probonopd]

I'd happily accept a Pull Request, as long as it has enough if statements so as to not interfere with previous versions of Fedora, CentOS, and the like.

[probonopd]

PR welcome.
Also see https://github.com/thias/glim/blob/master/grub2/inc-fedora.cfg