Perhaps the command exit or quit would work.

systemctl poweroff

Also, /sbin/shutdown is a symlink to /usr/bin/systemctl.

shutdown -r now

or
shutdown reboot now

you can but a time on it instead of now, and alert all logged in users
but I have never done that , i want it now and I'm the only user

man shutdown

Shutdown is a symlink to systemctl. As a symlink, it is subject to future deprecation. Linuxmint is run by systemd, thus systemctl is the actual binary responsible for shutdown. If you really want simple or less typing, try (seven strokes):

shutdown
is 6 if you are happy to wait a 1 minute

shut<tab><enter>

unless you have something else starting shut
:P

This one suggests it's worth a try to start a Gnome session. Try logging in as normal user on tty3 (Ctrl-Alt-F3 from a black screen if necessary), then do:If this doesn't produce a GUI desktop of some kind instead of errors, try the same logged in as root or with sudo. Error messages from either would be useful to know here. Whether this can work I don't know, because the last time I installed Gnome was about two decades ago and I don't plan to do it again in the foreseeable future. To make startx run as normal user might require first you do:Yet more to try if all the above fails, if not first:Make a note of where the asterisk appears, then choose any of the other options, then reboot normally. If still no joy, repeat with another selection. If still no joy and there is another option to select, try it. Doif you get stuck and don't want to wait for us to see what your results are to this point.

init 6 means reboot, not shutdown, which is 0, unless systemd changed that too. I don't think it did:

6 key presses since we started getting silly counting strokes

but I take the point that it might get depreciated

First, I was unable to use Ctrl-Alt-F3 from either a black screen, or any time during start-up. The screen simply remained black. So, using Escape at start-up I went into recovery mode and got to the root shell prompt.

Once there, I tried startx /usr/bin/gnome-session | pastebinit
The screen looked interesting for a second, the came back to black screen and told me I was trying to send an empty document. It left me with a blinking cursor and no way to type or to get back to the root shell prompt.

After restarting the process, I tried sudo startx... and nothing.

Next I tried: sudo apt install xserver-xorg-legacy (Sorry, I still can't figure out how to activate the "quote" cut and paste feature.) I got the following result: https://pastebin.com/LAVeyTTZ

Afterwards, I tried "startx /usr/bin..." again, and got nothing. Same for "sudo startx..."

Then I tried: sudo update-alternatives --config x-session-manager, and I received the following result:
https://pastebin.com/9eaEX1MV

I could not find an asterix anywhere on the screen, but did see this reference: "(**) from config file," ?? I was not given "any of the other options" so I was unable to "repeat with another selection".

Because I was not given any options, I have not yet tried: man update-alternatives

At this point I want to clarify our process. It seems that I have a defective light display manager, and that it may be either hardware- or software-related. Right? At this point we are simply attempting to get more information about the particular problem in order to determine how we can resolve it. Is this correct?
Thanks again.

yeah, I doubt X will run in recovery mode

In the past you have not been put into recovery mode.
Is that correct?

I have done everything in this thread in recovery mode with the root shell prompt. I have no other choice/option that I am aware of.

From an earlier post of mine you might have missed:

Toddly, unless proceeding to try to fix this is mainly or purely a learning exercise for you, and given the great degree of difficulty you have had pursuing our suggestions, us keeping straight what you have and haven't succeeded to do, and the length of this thread making attempts to help increasingly difficult, I suggest it may be time to abandon repair and install fresh. If you take this new path, you may wish to consider adding the new installation alongside (multiboot) instead of wiping out the old, so that you can pursue repair in the interest of education later on sometime.

Well toddly, seems you're not alone. On an old laptop I rarely use, that has Ubuntu on it, I tried an upgrade from (I think) Xenial to Bionic, and it's now broken. My recent upgrade on my Debian desktop (from 9 to 10) went okay, though in that case I was careful to check out release notes and such, rather than impulsively ploughing ahead as I did with the old laptop. Anyway, I shan't hijack this thread with my own problems (I'll likely start a new thread on it).

Try the option dpkg. It will reconfigure your install and try to fix it. It's nice and automatic (I'm just discovering this for myself). [edit] This (the dpkg option) did fix the issues I was having with booting into my laptop after upgrading it. So, it may help your issue. Worth a try, IMO.

I will try the dpkg command in recovery mode and see if it resolves the dead Light Display Manager issue. If it does not, then I may try to start a new thread dealing just with the LDM issue.
I've been incommunicado for weeks because the old laptop I was using to communicate about my other Linux laptop also died. I was left with no means of going online.
I feel this thread has been a big learning opportunity for me, and I can now understand more of what people are asking of me. Initially, all the jargon seemed like another language.
In any case, I'll report back about the dpkg effort.
Thanks everybody!!

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