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Written by Mike
August 11, 2009
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The definition and functionality of system checkpoints can be demonstrated on the example of NMC command:
nmc$ show appliance checkpoint
Show history of upgrades and system updates, in terms of system checkpoints and their properties.
First, the terms. Throughout the product, the terms "system folder", "root filesystem", and "checkpoint" are used interchangeably. The appliance's root filesystem (rootfs) contains OpenSolaris kernel and system configuration.
Example:
nmc$ show appliance checkpoint
ROOTFS CREATION CHECKPOINT-TYPE CURRENT DEFAULT VERSION
rootfs-nmu-005 Jul 30 14:37 rollback No No 1.1.9b104
rootfs-nmu-004 Jul 20 10:37 rollback No No 1.1.9b104
rootfs-nmu-003 Jun 04 18:15 upgrade Yes Yes 2.0.0b104
rootfs-nmu-002 Apr 22 9:31 upgrade No No 1.1.7b104
rootfs-nmu-001 Mar 25 10:31 rollback No No 1.1.4b104
rootfs-nmu-000 Feb 17 13:27 initial No No 1.1.4b104
In the example above, the current (active) checkpoint corresponds to version 2.0.0 of the NexentaStor. The printout also shows that this appliance was initially installed on Feb 17 (the year 2009 is removed here for shortness sake), and underwent several software upgrades, some of them in-place or "live upgrades" denoted in the table above as "rollback" checkpoints.
In particular, the last two upgrades in the example table shown above were of the type "rollback", which means: live upgrade not requiring reboot. For details on the types of software upgrades and discussion, please refer to NexentaStor User Guide.
Note that you can always reboot into any of the existing checkpoints - each checkpoint shows up in the GRUB boot menu, with the default one (DEFAULT = Yes) used by GRUB to boot the appliance.
In fact, you can go back and forth between the checkpoints without compromising any of the remaining checkpoints in any way. Each checkpoint is a complete Operating System which was snapshot-ed at some point. In the example above, this point in time is shown as CREATION column in the table of checkpoints.
Notice the CURRENT and DEFAULT columns. CURRENT = Yes indicates the current active checkpoint - the checkpoint you are currently in. DEFAULT = Yes indicates the default checkpoint from the boot manager
perspective - the one that the appliance will boot by default, unless you manually select another one in a GRUB menu.
Typically, DEFAULT = CURRENT and both point to the same checkpoint (like in the example above).
One common question is why the date on the current active checkpoint is older than the date on some other listed checkpoints?
This is, again, because of the live upgrade mechanism. In the example above the root filesystem created on June 04 was in-place upgraded two times, to eventually contain version 2.0. The creation time
however, did not change.
See also: