Firmware

According to https://wiki.mikrotik.com/wiki/SwOS/RB250_RB260#Summary

new RB260GS (CSS106-5G-1S), new RB260GSP(CSS106-1G-4P-1S) supports SwOS v2.0 and newer.

Probably not correct urls for our CSS106-5G-1S:

https://download2.mikrotik.com/swos2/css106/swos-css1061g4p1s-2.0.bin
https://download2.mikrotik.com/swos2/css106/swos-css1061g4p1s-2.2.bin

version

from web interface

Firmware
Current Installed Version	2.7 (built at Fri Dec 15 2017 09:42:48 GMT+0100 (CET))
Latest Available Version	2.7 (built at Fri Dec 15 2017 09:42:48 GMT+0100 (CET))

reset

hold reset while poweron

SwOS v2.x - RB260GS(CSS106-5G-1S) and RB260GSP(CSS106-1G-4P-1S)

The new RB260GS(CSS106-5G-1S) and RB260GSP(CSS106-1G-4P-1S) has built-in backup SwOS firmware which can be loaded in case standard firmware breaks or upgrade fails:

Holding Reset button for few seconds while device is booting resets configuration and loads backup firmware SwOS 2.0p.
After loading backup firmware SwOS 2.0p it is possible to connect to 192.168.88.1 using web browser and install new SwOS firmware.

default ip: 192.168.88.1

Current Installed Version	2.0p (built at Fri Oct 21 2016 10:18:39 GMT+0200 (CEST))
Latest Available Version	2.7 (built at Fri Dec 15 2017 09:42:48 GMT+0100 (CET))

Linux setup

dpavlin@x230:~$ sudo ifconfig enp0s25 192.168.88.240