The following will extract the public key from a private key.  This assumes your private key is call id_rsa and public key is called id_rsa.pub.  This can also be used to validate a public/private key are a match.

ssh-keygen -y -f .ssh/id_rsa

This should match the output of the following:

cat .ssh/id_rsa.pub

Create a User based service file:

cd ~/.config/systemd/user
podman generate systemd CONTAINER-NAME > container-CONTAINER-NAME.service

Edit the service file and comment out the PID= section. The allows you to not have to create a new service file each time you re-create the container.

Reload the systemctl dameon as root:

systemctl dameon-reload

Enable/start the service up. Do this as the user it will run as:

systemctl --user enable container-CONTAINER-NAME
systemctl --user start containre-CONTAINER-NAME

Upgrading via the Software application can have issues.  If it has any issues at all it just fails leaving your system partially upgraded.  This method is much safer and give you the ability to fix any issues as you find them.  Also don't try to jump more than 2 versions at a time (ie. 35 to 37).

Before you even get started I like to backup my grub.conf file and remove all kernels accept the current one just to get a cleaner start:

To remove file in Linux that has a hyphon or dash in front of it just prefix it with "./".  For example:

rm ./-testfile

1. power off the pi, remove the MicroSD card, and put that in a PC.
2. Then in the drive called "boot", create a file named "octopi-password.txt"
3. In that text file ("octopi-password.txt") you only need the password you want to set for the "pi" user, nothing else.  So it will be one word only in this file. 
4. Now take the MicroSD out of the PC, install it in the pi and boot it. 
5. You can now log in again using SSH, with username "pi" and the password you set in the file "octopi-password.txt".

To use journalctl to view the logs of the last reboot use the following:

journalctl --boot=-1

This command is handy for viewing logs right before a crash. Do the above command then use shift-g to go to the bottom of the list.

To find the install history of a specific RPM do the following:

rpm -q  --last

To find the install history of all RPMs do the following:

rpm -qa --last

NOTE: This will not sort them by install date.

Run the following command to connect

openssl s_client -connect {server}:{port} -starttls smtp

Then find out what authentication is supported. It should now show "AUTH LOGIN" now that you have an encrypted connection:

ehlo {domain.com}

If you see "AUTH LOGIN" in the list then do the following:

List all zones:

 firewall-cmd --list-all-zones

List all active zones:

firewall-cmd --get-active-zone

To add a host or network to allow all connections from:

firewall-cmd --permanent --zone=trusted --add-source=10.10.10.10

Add a service to be allowed from anywhere:

firewall-cmd --permanent --add-service=smtp

When you run firewall-cmd with the "--permanent" it will not be active until the dameon is reloaded. Do the following to make them active:

firewall-cmd --reload