This depends a lot on the type/source of the freeze. What were you doing at the time? Are you experiencing regular crashes? What is your hardware like? (laptop/desktop, year, make, model)

Is it just the window manager/desktop environment? Ctrl + Alt + F7 should take you to a different TTY session where you can login and give a reboot command. (actually any F# key should work)

The sysreq keys should always work if the OS is locked up. How are you using REISUB? Do you know what instruction each letter sends? Are you waiting in between pressing them? If using this "borked your PC", the most likely reason is that your system was busy writing something to the hard drive that is related to the OS and was interrupted. How was it "borked"? Did your bootloader start? Did your OS try to start?

One thing you can do if nothing seems to be responding is tap the NumLock key. If the indicator light changes you know 3 things:

1. The keyboard is working.
2. The USB driver and OS are actively responding to input devices, even if the display is frozen.
3. The CPU is alive and not stuck.

If the light changes then you should be able to tap the power button for a soft reset/graceful shutdown.

If the light does not change then you should first check your keyboard (is it plugged in? is it wireless? does it need a new battery?) but if that's not the problem then all you can do is force a shut down, because the system is not responding to input.

There are a lot of potential problems that can produce a "freeze", with the most basic being an issue with the mouse/keyboard or the USB port they're plugged into. I once thought my computer was freezing because I was using a Logitech wireless mouse that was bound to 2 different USB receivers plugged into different computers, and the input would randomly switch from one to the other (seriously check the simple stuff first). You could also have a problem with your RAM, hard drive, GPU, CPU or motherboard which could each produce symptoms like freezing. If you have regular crashes you should be checking your hardware.

To really answer the question "what can I do?" requires more context, and requires you to do some checking to judge the severity of the crash.

Sometimes the freeze might be in the display manager. Eg xorg or your wayland compositor has crashed.

In that case, you can use keyboard controls to change tty and fall back to a text interface. I think it's ctrl + alt + Fn$number, where $number will correspond to the tty you want. Most graphical sessions launch on tty2, so you would use crtl + alt + F1 to switch to tty1.

From there you can log in and use terminal commands to launch a new gui session, or to try and debug what went wrong. Generally, I've only had freezing issues on Linux when my GPU is dying. There was also a period where my work computer didn't have enough swap space. It would freeze whenever I tried to compile code during a video call.

Not that ever found. Ye Olde Power Button. And it does on rare occasion bork something.

I highly recommend keeping /home on a separate partition from / so that if worse comes to worst, you can reinstall the system and lose pretty much nothing. Most of the time it's no problem. But sometimes it is.

On Mint this might not be an issue because you should have swap. But an Out Of Memory situation on Linux is basically non-recoverable (or, not fun -- reboot is quicker).

Try running earlyoom in a tmux session to see if that prevents future crashes.

Ctrl-alt-backspace should restart the window manager.

ctrl+alt+ the function keys generally switches to a console interface.

I don't use Mint anymore, but I remember sometimes having some success with switching to a console and back.

magic sys req

No, there's no proper equivalent to Ctrl-Alt-Del. It's a major flaw in the Linux desktop. You just have to hard-reboot.

Edit: Downvotes, but you won't get any suggestions that match Ctrl-Alt-Del. Only

• Ctrl-Alt-Fn - Disabled by default in lots of distros I think, and it doesn't have high priority so it's not guaranteed to respond like Ctrl-Alt-Del does.
• Magic SysRq - Zero UI, so you have to magically remember a load of random keys, and there's no way to kill the specific offending process.
• Ctrl-alt-backspace - Brute force, kills X (does it even work on Wayland?).

Prove me wrong. Ctrl-alt-delete will respond even when the system is overloaded, and it lets me interactively see a list of processes and kill one of them. Can you do that in Linux?

Linux is never going to solve this problem while they treat the UI as "just another process".