Good Info:
https://www.interserver.net/tips/kb/install-lets-encrypt-cpanel-whm-server/
https://lowendtalk.com/discussion/106071/installing-free-ssl-for-server-hostname-using-letsencrypt

Login to the server via ssh andlLet’s run the following command to install Let’s Encrypt provider:

/scripts/install_lets_encrypt_autossl_provider

Once you have installed Let’s Encrypt provider, change auto SSL provider to Let’s Encrypt from cPanel (powered by Sectigo).

Login to WHM >> Manage AutoSSL.

Select Let’s Encrypt from cPanel (powered by Sectigo). Check the “I agree to these terms of service.”, and the “Recreate my current registration with “Let’s Encrypt”.

Install Self-Signed Certificate to Hostname.

Login to WHM as a root user. Go to “Service Configuration”.

Then select the following services and click on “Browse Certificate”. Calendar, cPanel, WebDisk, Webmail, and WHM Services, Dovecot Mail Server, Exim (SMTP) Server, FTP Server.

Select hostname and click on “Use Certificate”.

Then click on “Install”.

Restart cpsrvd

Replace Self Signed Certificates with Valid Let’s Encrypt Certificates.

Once you have installed the self-signed certificate, run the following command to check SSL certificates

/usr/local/cpanel/bin/checkallsslcerts --verbose

We can see the SSL CRT’s have been requested for your services. The hostname for the SSL CRT will be with one that is currently defined in cPanel:

# whmapi1 gethostname|grep hostname:
hostname: server1.hostname.com

While the process is not always this fast, after a few moments, we can see the SSL CRT’s are ready for install.
Then re-ran the ‘/usr/local/cpanel/bin/checkallsslcerts –verbose’ command which would have been ran at maintenance time. You may verify at WHM > Service Configuration > Manage Service SSL Certificates.

You can verify SSL installation by running https://server1.hostname.com:2087

WHM show the service as down.

Server domain.com
Primary IP Address 69.xx.xx.xx
Service Name ftpd
Service Status failed
Notification The service ?ftpd? appears to be down.
Service Check Method The system?s command to check or to restart this service failed.
Number of Restart Attempts 258
Startup Log 

Do the following…

# cd /var/run
# mv pure-ftpd.pid pure-ftpd.pid.bk

Restart ftpd in WHM under Service

A nice InnoDB Corruption Repair Guide

https://forums.cpanel.net/threads/innodb-corruption-repair-guide.418722/

1. Assign the Nameserver IP Addresses in WHM

In WHM, navigate to the left hand menu option “Basic cPanel/WHM Setup” and do the following:

Set the Primary Nameserver to ns1.yourdomain.com.
Then click Assign IP Address.
Repeat this for the Secondary Nameserver section, using ns2.yourdomain.com.
On the bottom of the page, click Save.

2. Setup the Nameserver a Records in WHM

While still in the “Basic cPanel/WHM Setup” section, do the following:

Beside the Primary Nameserver entry, click the “Add an A record entry for this nameserver” button
Repeat this for the Secondary Nameserver section

If you have already created a hosting account on your cPanel server for the domain you are using for your nameservers, performing the A record creation steps above should just create an entry for each nameserver in the existing DNS zone for the domain. However, if you have not yet(or do not intend to) set up a hosting account for the nameserver domain, the steps above will create individual DNS zones for each nameserver you have setup.

NOTE: If you are not hosting the main domain used for the nameservers on the same server, you will need to ensure you have added A records for the nameservers into the DNS zone for the domain with the domain hosting provider.
3. Restart the DNS Service

You should now just be able to restart the DNS service by doing the following:

Navigate to the “Restart Services” section in the left hand men;
Select “DNS Server (BIND/NSD)”
Hit the yes button in the right hand frame.

4. Register Your Nameserver Hosts with Your Domain Registrar

Before the nameservers we’ve just set up in WHM will work, you need to make sure that the correct details have been configured with your domain registrar. Each registrar handles the setting up of private nameservers differently so you should contact them to determine the method they use. Some let you control the setup from your domain control panel, however some require their administrators to create the nameserver entries for.

The most important point to make when contacting your registrar is that you wish to create private nameserver hosts to use with your own hosting server(some refer to these as child nameservers or domain hosts). Occasionally you will strike level 1 support staff who do not fully understand what you wish to do and may provide you incorrect instruction unless you specify this.

Once you know how they do it, you just need to set up the nameservers in their system as below:

Enter the names you would like to use; e.g. ns1.yourdomain.com and ns2.yourdomain.com
Enter the corresponding ip addresses details from your server that you wish to use.

Done!…Hopefully you now have working nameservers attached to your own domain.

cPanel default backup system may fail to create and save backup of your server and send you following message:
The backup was not able to be completed because timed out waiting for /bin/backup to finish

Possible cause of the problem

Any old backup process is still running in background on the server.

Login to your server as root via SSH and execute following command

# /usr/local/cpanel/bin/backup --force

Most probably it will show you following type message:

Backup process currently running. Pid: 5378
Backup log file: /usr/local/cpanel/logs/cpbackup/1377934812.log

Solution

We need to kill the current running backup process. Note the Pid from above and run following command. Change xxxx to Pid number that you have got from above.

# kill -9 xxxx

cPanel backup should now run normally. You can force to start a new fresh backup process using below command:

# /usr/local/cpanel/bin/backup --force

Sending email with WHM/cPanel and the error is:

Number of failed recipients exceeded. Come back in a few hours.

Check WHM Settings

Login to WHM and go to Home » Server Configuration » Tweak Settings. Click the Mail tab. Find “Number of failed or deferred messages a domain may send before protections can be triggered [?]”

Change to a higher number and save.

Home » Service Configuration » Exim Configuration Manager » ACL Options

Ratelimit incoming connections with only failed recipients [?]
Ratelimit incoming SMTP connections that have only sent to failed recipients five separate connection times in the last hour.

Try turning off or if you are sending to multiple emails , verify the emails as this will be usually when multiple emails fail.

Also, check tweak settings

Home » Server Configuration » Tweak Settings
Also – there is this:

/var/cpanel/email_send_limits/max_deferfail_example.com

Deleting this file fixed the problem immediately. I’m guessing that the system should have deleted (or updated?) this file at some point, but didn’t.

And,

You can modify the “Maximum Hourly Email by Domain Relayed” and “Maximum percentage of failed or deferred messages a domain may send per hour.” values for an account via:

“WHM Home » Account Functions » Modify an Account”