31.10.2017 20:45, Austin S. Hemmelgarn пишет: > On 2017-10-31 12:23, ST wrote: >> Hello, >> >> I've recently learned about btrfs and consider to utilize for my needs. >> I have several questions in this regard: >> >> I manage a dedicated server remotely and have some sort of script that >> installs an OS from several images. There I can define partitions and >> their FSs. >> >> 1. By default the script provides a small separate partition for /boot >> with ext3. Does it have any advantages or can I simply have /boot >> within / all on btrfs? (Note: the OS is Debian9) > It depends on the boot loader. I think Debian 9's version of GRUB has > no issue with BTRFS, but see the response below to your question on > subvolumes for the one caveat. >> >> 2. as for the / I get ca. following written to /etc/fstab: >> UUID=blah_blah /dev/sda3 / btrfs ... >> So top-level volume is populated after initial installation with the >> main filesystem dir-structure (/bin /usr /home, etc..). As per btrfs >> wiki I would like top-level volume to have only subvolumes (at least, >> the one mounted as /) and snapshots. I can make a snapshot of the >> top-level volume with / structure, but how can get rid of all the >> directories within top-lvl volume and keep only the subvolume >> containing / (and later snapshots), unmount it and then mount the >> snapshot that I took? rm -rf / - is not a good idea... > There are three approaches to doing this, from a live environment, from > single user mode running with init=/bin/bash, or from systemd emergency > mode. Doing it from a live environment is much safer overall, even if > it does take a bit longer. I'm listing the last two methods here only > for completeness, and I very much suggest that you use the first (do it > from a live environment). > > Regardless of which method you use, if you don't have a separate boot > partition, you will have to create a symlink called /boot outside the > subvolume, pointing at the boot directory inside the subvolume, or > change the boot loader to look at the new location for /boot. > > From a live environment, it's pretty simple overall, though it's much > easier if your live environment matches your distribution: > 1. Create the snapshot of the root, naming it what you want the > subvolume to be called (I usually just call it root, SUSE and Ubuntu > call it @, others may have different conventions). > 2. Delete everything except the snapshot you just created. The safest > way to do this is to explicitly list each individual top-level directory > to delete. > 3. Use `btrfs subvolume list` to figure out the subvolume ID for the > subvolume you just created, and then set that as the default subvolume > with `btrfs subvolume set-default /path SUBVOLID`. Once you do this, > you will need to specify subvolid=5 in the mount options to get the real > top-level subvolume.
Note that current grub2 works with absolute paths (relative to filesystem root). It means that if a) /boot/grub is on btrfs and b) it is part of snapshot that becomes new root, $prefix (that points to /boot/grub) in the first-stage grub2 image will be wrong. So to be on safe side you would want to reinstall grub2 after this change. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
