Category: Hardware

APC SmartUPS 750, apcupsd and power failure: what exactly happens, where “UPS Rbt off” and “UPS StayOff” come from and which delays are configurable and which are not

In theory, an Uninterruptable Power Supply (UPS)’s workings such as the APC SmartUPS 750 in connection with an attached PC are trivial: when power fails and battery capacity runs low, the PC is shut down. When power returns, the PC is turned on again. In reality, there can be confusing messages such as UPS Rbt… Continue reading APC SmartUPS 750, apcupsd and power failure: what exactly happens, where “UPS Rbt off” and “UPS StayOff” come from and which delays are configurable and which are not

Bringing OpenWrt to the Mikrotik hAP lite (RB941-2nD-TC)

In a previous post I described the Mikrotik hAP lite (RB941-2nD-TC) and its RouterOS and already suggested that I prefer to run OpenWrt on it. Because Mikrotik routers behave a bit different than the usual TP-Link, GL.iNet etc. devices and because there were some pitfalls I had to master myself, here’s some advice to keep… Continue reading Bringing OpenWrt to the Mikrotik hAP lite (RB941-2nD-TC)

Choosing a cheap but maintained/maintainable LAN router

Recently I’ve been tasked with the problem of finding a router that had to fulfill five key requirements: it had to offer in total four to five LAN ports, have an internal or a detachable Wifi antenna (if at all), offer a maintained/maintainable firmware, be compact and, most of all, better be cheap, for a… Continue reading Choosing a cheap but maintained/maintainable LAN router

Using a reverse SSH tunnel to provide an isolated system such as a Raspberry Pi with network access (well, HTTP)

Imagine you have a system to which you can only SSH inbound but which is unable to reach any host on the Internet outside the local network. For instance, you might have tightened down network access to secure a local CA. Or, like me, you have a Raspberry Pi that you carried around with you… Continue reading Using a reverse SSH tunnel to provide an isolated system such as a Raspberry Pi with network access (well, HTTP)

Samsung Galaxy phones: Low-level backup of encrypted /data partition with TWRP

If you use an Android phone such as the Galaxy S7, you’ll have noticed that there is an “internal storage”, sometimes also shown as “internal SD card”, which in the latter case is somewhat misleading since it is no SD card but part of the internal flash memory. Whereas the “external storage” or “external SD… Continue reading Samsung Galaxy phones: Low-level backup of encrypted /data partition with TWRP