Yeah, trying to learn what something is from man pages can be rough.
It's a way to safely upgrade. "Safely" means I can easily downgrade without having to mess with a rescue disk. Mostly I have had to downgrade after playing with, err, dangerous modules like virtualbox and drm.
Example use:
DRM won't work at all on my Skylake laptop unless I install
graphics/drm-stable-kmod. There was an update a few days ago. So I created a new boot environment (BE):
beadm create 11.2Rp2_DRM_Aug22
then I activate it:
beadm activate 11.2Rp2_DRM_Aug22
This means it will be the active BE when I reboot.
Then I reboot and install the latest
graphics/drm-stable-kmod .
Code:
>beadm list
BE Active Mountpoint Space Created
default - - 3.2G 2018-07-03 15:14
11.2Rp2_DRM_Aug2 - - 563.9M 2018-08-03 15:15
11.2Rp2_DRM_Aug22 NR / 16.4G 2018-08-23 10:07
What beadm did:
Code:
>zfs list -t snapshot
NAME USED AVAIL REFER MOUNTPOINT
zroot/ROOT/11.2Rp2_DRM_Aug22@2018-07-10-21:29:56 3.22G - 8.99G -
zroot/ROOT/11.2Rp2_DRM_Aug22@2018-08-23-10:07:21 563M - 12.4G -
>zfs list
NAME USED AVAIL REFER MOUNTPOINT
zroot 284G 146G 96K /zroot
zroot/ROOT 16.4G 146G 88K none
zroot/ROOT/11.2Rp2_DRM_Aug2 896K 146G 12.4G /
zroot/ROOT/11.2Rp2_DRM_Aug22 16.4G 146G 12.6G /
zroot/ROOT/default 912K 146G 8.99G /
If suspend to ram broke with Aug 22 drm or other bad things happen, I can revert to the zroot/ROOT dataset to Aug 2 by activating and rebooting into the old Aug2 BE. If really bad things happen and I can't even boot, the beastie loader menu allows me to select any BE, overriding the active (11.2Rp2_DRM_Aug22) one.
beadm rolling back will not affect other datasets so usr/home, usr/ports/, usr/src do not get rolled back.
beadm won't work if you have changed the default zfs datasets created by the installer or are using disk encryption.
I found
Michael W. Lucas's not too detailed explanation of how beadm works very helpful, especially the bit explaining exactly what does and doesn't get rolled back. Before understanding this, I was afraid to mess with beadm.
