Oracle Linux 7 installation allows you to create a btrfs root file
system. The mounted root file system is a snapshot (named
install
) of the root file system taken at the
end of installation. To find out the ID of the parent of the root
file system subvolume, use the following command:
# btrfs subvolume list /
ID 258 top level 5 path install
In this example, the installation root file system subvolume has
an ID of 5. The subvolume with ID 258 (install
)
is currently mounted as /
.
Figure 21.1, “Layout of the root File System Following Installation” illustrates the layout
of the file system:
The top-level subvolume with ID 5 records the contents of the root
file system file system at the end of installation. The default
subvolume (install
) with ID 258 is currently
mounted as the active root file system.
The mount command shows the device that is currently mounted as the root file system:
# mount
/dev/mapper/vg_btrfs-lv_root on / type btrfs (rw)
...
To mount the installation root file system volume, you can use the following commands:
#mkdir /instroot
#mount -o subvolid=5 /dev/mapper/vg-btrfs-lv-root /instroot
If you list the contents of /instroot
, you can
see both the contents of the installation root file system volume
and the install
snapshot, for example:
# ls /instroot
bin cgroup etc install lib64 misc net proc sbin srv tmp var
boot dev home lib media mnt opt root selinux sys usr
The contents of /
and
/instroot/install
are identical as demonstrated
in the following example where a file (foo
)
created in /instroot/install
is also visible in
/
:
#touch /instroot/install/foo
#ls /
bin cgroup etc home lib media mnt opt root selinux sys usr boot dev foo instroot lib64 misc net proc sbin srv tmp var #ls /instroot/install
bin cgroup etc home lib media mnt opt root selinux sys usr boot dev foo instroot lib64 misc net proc sbin srv tmp var #rm -f /foo
#ls /
bin cgroup etc instroot lib64 misc net proc sbin srv tmp var boot dev home lib media mnt opt root selinux sys usr #ls /instroot/install
bin cgroup etc instroot lib64 misc net proc sbin srv tmp var boot dev home lib media mnt opt root selinux sys usr