My Cubie crashed after 3-4 weeks and I installed Watchdog using the file change method.
During my tests it works fine several times.
But again after 3-4 weeks my Cubie was totally unavailable via SSH & console.

Title:                  Armbian 4.81 Cubietruck Debian jessie dev (unofficial)
Kernel:                 Linux 2016.01-rc3
Build date:             28.12.2015

Filesystem      Size  Used Avail Use% Mounted on
/dev/root       917G  4.3G  867G   1% /
devtmpfs        944M     0  944M   0% /dev
tmpfs           944M     0  944M   0% /dev/shm
tmpfs           944M   17M  927M   2% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           944M     0  944M   0% /sys/fs/cgroup
/dev/nand1       32M  8.9M   24M  28% /boot
tmpfs           256M     0  256M   0% /tmp

I did now an update to the latest build version, but any ideas what can be the reason?

ty in advance
 

Instability can be connected with poor power supply, too high (uboot) dram frequency, ... if you don't have anything else connected to the board, except network. Those a20 boards are running stable for some time, but particular combination of u-boot / kernel could be buggy.

understood. ty so much for your prompt view on this.

Forgot to mention that a Lipo-USV supply is also in place.

Okay, I will do regular reboots before I am going to holiday...