Sailfish OS ‑ Command Line Interface & Customisation
MTP (the same protocol Android devices use) will expose the /home/nemo folder to the connecting computer, both to graphical and command line applications. But it hides some files and folders from the connected system. A more powerful way is to connect through a terminal via SSH, as explained here.
Sailfish OS ‑ Auto‑mount encrypted memory card at boot
There are other approaches to this involving udev rules to unlock & mount every time you insert/remove the card. This is different - the idea is that the memory card mostly stays where it is and that apps can rely on it being mounted. Manual un/mounting, removal and insertion, is still possible though.
AdBlocking on Sailfish OS via /etc/hosts
There are some apps in Openrepos which do not seem to work anymore for SFOS 4.x. But you don't really need an app, all you need is a systemd timer & service and a simplistic shell script. Gain command line access to your phone and become root. hosts.timer:
Sailfish OS ‑ Persistently set "modes" from the command line
Tools for interacting with mce (Mode Control Entity). Provides the command line tool mcetool which allows to set and read various - well, modes on your phone. E.g.: disable lock screen animation: AFAICS it is not possible to get the status of only 1 control; you need to grep for it:
The phone will alert you that there's an update. Go to Settings => Sailfish OS Updates. As always, backup first. Download the update and choose to install it. Once again it complains that I don't have enough space on the root filesystem. This time I decide to bite the bullet and expand the root volume.
Making sshd more secure on Sailfish OS
Recent versions of Sailfish OS (currently 126.96.36.199) use a socket that listens on port 22, and start sshd (to be precise, a per-connection sshd@.service) whenever someone knocks. Pretty neat, probably saves some resources when you don't need an ssh connection.
Sailfish OS ‑ Applications
A.k.a "sailfish-browser". Its settings are not accessed from a pulldown but from the main app menu => Settings => Apps => Browser. There isn't much. Most notably: no (to me) acceptable search engine. But you can install the Search engines manager from OpenRepos.net, which allows you to search, add & remove search engines.
Getting started with Sailfish OS
I was lucky to get a device that already comes with Sailfish OS 3 preinstalled. This is the most recent free version of Sailfish OS; I assume I will be able to upgrade it to Sailfish X (same version + Android support) if I want to. If you need to start from scratch (you will need a Jolla account), instructions are here.