let’s first assume the contents of /etc/fstab are either not used or invalid in mounting the subvolumes. given the following ‘df’ command, how do i know which subvolume of the btrfs filesystem on /dev/sda3 is mounted at each mount point (/, /var, /opt, /home)? i would have expected to see the mount option used to define the subvolume (subvolid or subvol option) in /proc/mounts. # df Filesystem 1K-blocks Used Available Use% Mounted on /dev/sda3 6839296 1698564 4903212 26% / devtmpfs 501464 0 501464 0% /dev tmpfs 507316 0 507316 0% /dev/shm tmpfs 507316 6720 500596 2% /run tmpfs 507316 0 507316 0% /sys/fs/cgroup /dev/sda3 6839296 1698564 4903212 26% /var /dev/sda3 6839296 1698564 4903212 26% /opt /dev/sda3 6839296 1698564 4903212 26% /home /dev/sda1 517868 93040 424828 18% /boot # btrfs subvolume list -a --sort=+rootid / ID 257 gen 7800 top level 5 path <FS_TREE>/root ID 258 gen 4127 top level 5 path <FS_TREE>/home ID 259 gen 7801 top level 5 path <FS_TREE>/var ID 260 gen 7795 top level 5 path <FS_TREE>/opt # uname -a Linux turner11.storix 3.10.0-123.el7.x86_64 #1 SMP Mon May 5 11:16:57 EDT 2014 x86_64 x86_64 x86_64 GNU/Linux # btrfs --version Btrfs v3.12 # btrfs fi show Label: rhel_turner11 uuid: cd3c0e50-d726-44e2-9bfa-19b11614136a Total devices 1 FS bytes used 1.62GiB devid 1 size 6.52GiB used 2.24GiB path /dev/sda3 Btrfs v3.12 # btrfs fi df / Data, single: total=1.98GiB, used=1.58GiB System, single: total=4.00MiB, used=16.00KiB Metadata, single: total=264.00MiB, used=36.03MiB