Solaris 11.4 SRU 75: Creating a clone in .clone

In the .zfs directory of a ZFS filesystem there are a few subdirectories. One of them is .zfs/snapshot. I think many of you know the trick that you can create a snapshot by just doing a mkdir in this directory.

Let`s fill our filesystem with some stuff:

root@testbed:/tank/test2# touch monday 
root@testbed:/tank/test2# touch tuesday 
root@testbed:/tank/test2# touch wednesday 
root@testbed:/tank/test2# ls
monday     tuesday    wednesday

Now we go into the .zfs/snapshot directory.

root@testbed:/tank/test2# cd .zfs 
root@testbed:/tank/test2/.zfs# cd snapshot/
root@testbed:/tank/test2/.zfs/snapshot# ls
root@testbed:/tank/test2/.zfs/snapshot# mkdir 26032025_0527
root@testbed:/tank/test2/.zfs/snapshot# cd 26032025_0527/
root@testbed:/tank/test2/.zfs/snapshot/26032025_0527# ls
monday     tuesday    wednesday
root@testbed:/tank/test2/.zfs/snapshot/26032025_0527# touch test 
touch: cannot create test: Read-only file system
root@testbed:/tank/test2/.zfs/snapshot/26032025_0527#

As it’s a snapshot, you can`t make any changes to it. It’s a read-only filesystem.

Sometimes it would be quite practical to be able to write into such a snapshot. Well, there is now a .zfs/clone subdirectory and you can do the same for ZFS clones. Just a a different directory. Execute an mkdir there and a clone is created.

root@testbed:/tank/test2/.zfs/clone# cd /tank/test2/.zfs/clone
root@testbed:/tank/test2/.zfs/clone# mkdir c26032025_0527
root@testbed:/tank/test2/.zfs/clone# cd c26032025_0527/
root@testbed:/tank/test2/.zfs/clone/c26032025_0527# ls
monday     tuesday    wednesday
root@testbed:/tank/test2/.zfs/clone/c26032025_0527# touch thursday 
root@testbed:/tank/test2/.zfs/clone/c26032025_0527# ls
monday     thursday   tuesday    wednesday
root@testbed:/tank/test2/.zfs/clone/c26032025_0527# ls ../../../
monday     tuesday    wednesday

This clone allows you to write into the filesystem without changing the source of the clone.

Let’s assume you have created a clone with the normal commands:

root@testbed:~# zfs snapshot tank/test2@26032025_0549
root@testbed:~# zfs clone tank/test2@26032025_0549 tank/test20

By setting the mountpoint property to clonedir, the clone will now appear under `.zfs/clone

root@testbed:~# zfs set mountpoint=clonedir tank/test20
root@testbed:~# cd /tank/test2/.zfs
root@testbed:/tank/test2/.zfs# cd clone/
root@testbed:/tank/test2/.zfs/clone# ls
c26032025_0527  test20

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