TrueNAS supports a ZFS feature known as boot environments.
These are snapshot clones that TrueNAS can boot into.
Only one boot environment can be used for booting.
A boot environment allows rebooting into a specific point in time and greatly simplifies recovering from system misconfigurations or other potential system failures.
With multiple boot environments, the process of updating the operating system becomes a low-risk operation.
The updater automatically creates a snapshot of the current boot environment and adds it to the boot menu before applying the update.
If anything goes wrong during the update, the system administrator can boot TrueNAS into the previous environment to restore system functionality.
Go to System > Boot to see a boot environment list.
Managing Boot Environments
To view the list of boot environments on the system, go to System > Boot.
Each boot environment entry contains this information:
Name: the name of the boot entry as it appears in the boot menu.
Active: indicates which entry boots by default if a boot environment is not active.
Created: indicates the boot environment creation date and time.
Space: shows boot environment size.
Keep: indicates whether or not TrueNAS deletes this boot environment when a system update does not have enough space to proceed.
To access more options for a boot environment, click :
Only appears on entries which are not currently set to Active.
Activating an environment means the system boots into the point of time saved in that environment the next time it is started.
The status changes to Reboot and the current Active entry changes from Now/Reboot to Now, indicating that it is the currently booted environment but will not be used on next boot.
Copy the selected boot environment into a new entry.
The clone Name only allows alphanumeric characters, dashes (-), underscores (_), and periods (.) are allowed.
Changes the boot environment name.
Alphanumeric characters, dashes (-), underscores (_), and periods (.) are allowed.
Removes the highlighted entry and also removes that entry from the boot menu.
The default and any Active entries cannot be deleted.
Because an activated entry cannot be deleted, this button does not appear for the active boot environment.
To delete a currently Active entry, first activate another entry.
Toggles whether or not the updater can prune (automatically delete) this boot environment if there is not enough space to proceed with the update.
Click ACTIONS to:
Make a new boot environment from the active environment:
Only alphanumeric characters, dashes (-), and underscores (_) are allowed in the Name.
Name the new boot environment and click SUBMIT.
Display statistics for the operating system device: condition, total and used size, and date and time of the last scrub.
By default, the operating system device is scrubbed every 7 days.
To change the default, input a different number in the Automatic scrub interval (in days) field and click UPDATE INTERVAL.
Shows the status of each device in the operating system device (boot-pool), including any read, write, or checksum errors.
Perform a manual “scrub” (data integrity check) of the operating system device.
Changing Boot Environments
Sometimes, rolling back to an older boot environment can be useful.
For example, if an update process doesn’t go as planned, it is easy to roll back to a previous boot environment.
TrueNAS automatically creates a boot environment when the system updates.
There are two different methods for changing the active boot environment: using the web interface and through a Command Line Interface (CLI)
To activate a different boot environment, go to System > Boot and click more_vert for the desired boot environment.
Next, click Activate.
This boot environment shows Reboot in the Active column.
This means the boot environment becomes active on the next system boot.
The system configuration also changes to the state it was in when the boot environment was created.
If the web interface is inaccessible but physical access to the system is still possible, the boot environment can be changed at the welcome screen of the CLI.
Reboot the system.
When the welcome screen appears, press the key that corresponds with the option Boot Environments.
In the image below, the key to select the Boot Environments option is 7.
The Boot Environments options does not appear when no additional boot environments are present.
After selecting the Boot Environment option, choose the new boot environment to activate.
Press the corresponding key for the Active: option. In the picture below, the key is 2.
Press the key to cycle through existing boot environments.
When the desired boot environment is selected, press Backspace to return to the welcome menu.
Then, press 4 to reboot the system.
The selected boot environment is used when the system reboots.