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hyperknot
Asked: 2015-10-02 16:56:17 +0800 CST

"Reinstall" FreeBSD using ZFS snapshots

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I am using a dedicated server, and unlike on VPS providers or VM machines, getting back to a clean state (untouched, after install) is quite a laborious thing to do (lots of clicking around in a web control panel and launching Java KVM viewers + doing the installation manually).

My question is that given ZFS support for snapshots, would it be possible to get back to a clean state just by issuing a single command?

My ZFS partition table would be the "Auto (ZFS)" offer by the installer, which looks like this on my server (using FreeBSD 10.2):

NAME                 USED  AVAIL  REFER  MOUNTPOINT
zroot               34.8G   176G    96K  /zroot
zroot/ROOT          1.46G   176G    96K  none
zroot/ROOT/default  1.46G   176G  1.46G  /
zroot/tmp           76.8M   176G  76.8M  /tmp
zroot/usr           33.2G   176G    96K  /usr
zroot/usr/home      32.6G   176G  32.6G  /usr/home
zroot/usr/ports      631M   176G   631M  /usr/ports
zroot/usr/src         96K   176G    96K  /usr/src
zroot/var            692K   176G    96K  /var
zroot/var/audit       96K   176G    96K  /var/audit
zroot/var/crash       96K   176G    96K  /var/crash
zroot/var/log        204K   176G   204K  /var/log
zroot/var/mail        96K   176G    96K  /var/mail
zroot/var/tmp        104K   176G   104K  /var/tmp

My questions are the following:

  1. Is it possible to get back to this clean state using ZFS snapshots? What if I changed the kernel, deleted half the file-system, etc. Can a snapshot revert back everything like if it was just after installation?

  2. If yes, how can I do that? What command do I need to create the snapshot and what do I need to revert to one?

freebsd

1 Answers

  1. take a recursive snapshot of zroot

    zfs snapshot -r zroot@cleaninstall

    called cleaninstall and then revert it with

    zfs rollback zroot@cleaninstall
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