LINux on MOBile

At FOSDEM 2025, I had the opportunity to take care and demo some devices running Mobian at the LinuxOnMobile stand¹. When handling the Poco F1 with Mobian, I was once again reminded that having Phog as a greeter is IMHO a great choice, as it means that you don't need to unlock your keyring manually.²

This morning, on holidays in South Tyrol on the first day without plans but with clouds, I had the opportunity to finally try phrog on my Pixel 3a running postmarketOS edge (with Phosh, still openRC).

What the 🐸?

phrog/🐸, like phog, is a mobile-device greeter for Phosh. It uses libphosh and is written in Rust. As the README states,

phrog uses Phosh to conduct a greetd conversation.

You do not really need to understand the technical details to use it. Just think of it as something like gdm: You log in with it, and if you want, you can also choose a different graphical session, e.g., log into sway instead of phosh, assuming you have sway installed. Also, there's another use-case that may be relevant for device used by multiple users: With phrog, you easily login with different users. So if this was holding you back from going for that Mobile Linux family tablet, don't fret anymore!

Install and setup

Do not try this on a systemd-install of postmarketOS with Phosh!¹ If you are on 24.12, the instructions should work just as well, but I have not tried on one of my 24.12 phones yet.

If your device contains valuable data, make a backup first. It's recommended to enable the sshd service before experimenting, so that you can fix your install if something should go wrong!

Most of the install process is in Phrog's readme:

sudo apk add greetd-phrog

Then configure greetd to use Phrog (you can also edit /etc/conf.d/greetd and just add the line starting with cfgfile= if you prefer it that way):

cat <<HERE | sudo tee -a /etc/conf.d/greetd
cfgfile="/etc/phrog/greetd-config.toml"
HERE

After that, make sure greetd is run at startup:

sudo rc-update add greetd

If you want to make sure that worked, you can now reboot. greetd and Phrog will already be run, in fact, you should already be able to briefly see something black and green, to then end up in Phosh's standard login screen.

To really use phrog, there's one more step:

sudo rc-update del tinydm

This disables tinydm, the default display manager on postmarketOS that usually starts Phosh on postmarketOS. As now greetd/phrog starts Phosh, tinydm no longer needed.

Enjoy

Now, when you start your phone or log out of Phosh, your screen will look something like this:

Undoing (just in case)

If you, unlike me, should not like the Phrog experience, you can undo it by re-enabling tinydm

sudo rc-update add tinydm

and disabling greetd:

sudo rc-update del greetd

Afterwards, you can uninstall greetd-phrog.