On 05/07/2019 12:47, Remi Gauvin wrote: > On 2019-07-05 7:06 a.m., Ulli Horlacher wrote: > >> >> Ok, it seems my idea (replacing the original root subvolume with a >> snapshot) is not possible. >> > ... > It is common practice with installers now to mount your root and home on > a subvolume for exactly this reason. (And you can convert your current > system as well. Boot your system with a removable boot media of your > choice, create a subvolume named @. Move all existing folders into this > new subvolume. Edit the @/boot/grub/grub.cfg file so your Linux boot > menu has the @ added to the paths of Linux root and initrd.
Personally, I use a slightly different strategy. My basic principle is that no btrfs filesystem should have any files or directories in its root -- only subvolumes. This makes it easier to do stuff with snapshots if I want to. For system disks I use a variant of the "@" approach. I create two subvolumes when I create a system disk: rootfs and varfs (I separate the two because I use different btrbk and other backup configurations for / and /var). I then use btrfs subvolume set-default to set rootfs as the default mount so I don't have to tell grub, etc about the subvolume (I should mention that I put /boot in a separate partition, not using btrfs). In /etc/fstab I mount /var with subvol=varfs. I also mount the whole filesystem (using subvolid=5) into a separate mount point (/mnt/rootdisk) so I can easily get at and manipulate all the top-level subvolumes. Data disks are similar. I create a "home" subvolume at the top level in the data disk which gets mounted into /home. Below /home, most directories are also subvolumes (for example, one for my main account so I can backup that separately from other parts of /home). I mount the data disk itself (using subvolid=5) into a separate mount point: /mnt/datadisk -- which I only use for doing work with messing around with the subvolume structure. It sounds more complicated than it is, although it is not supported by any distro installers that I am aware of. And you should expect to get a few config things wrong while setting it up and will need to have an alternative boot to use to get things working (a USB disk or an older system disk). Particularly if you want to use btrfs-over-LVM-over-LUKS. And don't forget to fully update grub when you think is working and then test it again without your old/temporary boot disk in place! Basically, I make many different subvolumes and use /mount to put them into the places they should be in the filesystem (except for / for which I use set-default). The real btrfs root directory for each filesystem is mounted (using subvolid=5) into a separate place for doing filesystem operations. I then have a cron script which checks that every directory within the top level of each btrfs filesystem (and within /home) is a subvolume and warns me if it isn't (I use special dotfiles within the few top-level directories which I don't want to be their own subvolumes). Contact me directly if you would find my personal "how to set up my system and root disks, for debian, using btrfs-over-lvm-over-luks" notes useful. Graham
