I have always used control panels on my server, but over the years am becoming more familiar with the shell, and wondered whether I could ditch a control panel altogether and manually edit the files. I only host my own sites (less than 10) and only really need to administer the DNS, email and databases.
There are some really good guides on the Digital Ocean site on setting up a server and installing the various bits such as lamp, postfix, fail2ban etc
But I was wondering if there are any pitfalls I should be aware of? Is it easy enough to do everything manually? Or would something like Virtualmin be better? (I have used virtualmin in the past and think it's great).
CP's handle a lot of things behind the scenes with basic configuration/management. Don't take this for granted. They do also make managing multiple domains easier, but mostly if you have multiple users. If you feel comfortable getting dirty with the various daemons (apache, bind, postfix, mysql, etc) then you don't need a control panel regardless of how many domains. Once you get the basic configurations set, it's generally simple tasks to maintain and add further.
Using virtualmin would definitely be beneficial if you do not fully grasp what you are doing on the backend. We all have to start somewhere, and there's no shame in cheating your way through some of the more complex stuff.
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Cpanel is the best option in case of multiple accounts / domains. There is also the security matter. Can you be sure about your security configuration, by your own?
Cpanel representatives are there to help you with a ticket. If you are alone in this, then you maybe need some professional help with your server.
So, if you are sure about your configurations / security, you can keep up with your server, on your own. I wouldn't recommend other panel software (free) because you cannot request vulnerabilities check, decent updates, or any other kind of help.