An instability counter is used to detect system instability.

• If 16 consecutive reboots are detected due to a watchdog, a “backup restore” operation is triggered.
• If 32 consecutive reboots are detected due to a watchdog, a “stock restore” operation is triggered.

The counter is reset if the system is up during at least 10 minutes. This feature cannot be disabled as it avoids bricking the gateway in case of software failure.

The counter bootfail is displayed at boot time only if the reboot is due to a watchdog. Bootcause information are available here.

U-Boot 2015.04 (Aug 21 2018 - 18:53:11)

CPU:   Freescale i.MX6SX rev1.2 at 792 MHz
CPU:   Temperature 48 C
Reset cause: WDOG
       Watchdog enabled
I2C:   ready
DRAM:  240 MiB
MMC:   FSL_SDHC: 0
Using default environment

In:    serial
Out:   serial
Err:   serial
bootcause = SW
bootcount = 32
bootfail = 0
bootmode = nominal
boardconfig = 0x0
Net:   FEC0
Normal Boot

The updates that are being installed during an update request can make the system unstable so by default they are not included immediately in the backup.
Before each update, a “snapshot” of the firmware is done. It contains all the previously applied updates that are considered as “stable”. This “snapshot” will be used if a “backup restore” is triggered.
If a “backup recovery” is triggered, only the stable updates are restored. Other updates are destroyed.

Modifications in rootfs will be lost except system upgrade files.

This mecanism is divided in 2 elements:

• /etc/sysupgrade.conf: Contains the system (KerOS) elements to backup/restore.
• /etc/sysupgrade.d/: a directory with .conf files where additional elements to backup/restore can be added (i.e. by additional packages).

By default, some system configuration files are backed up like the network configuration.

To trigger a backup restore execute the following commands:

kerosd -b
reboot

The stock firmware is backuped at production time (or when updated with a KerOS liveburner.ipk file).
A “stock restore” will factory reset the station. All data will be lost. To trigger a stock restore execute the following commands:

kerosd -s 
reboot

This functionality from firmware < 4.0 must not be used to store configuration files. In order to save configuration use the sysupgrade management.