Question for experienced admins. Where to gain enough experience in the shortest possible time?

Question

MySQL

At my two previous jobs, exclusively Windows servers were used, telephony was analog and was serviced by the operator who supplied it, and MSSql on which the software bases were spinning, which, together with the server, was also serviced by those people who developed the software and supplied it to my employer. So I was exclusively involved in technical support for users, network maintenance and Windows servers. There was no way to get these skills there. And you just need to master them desperately, and in the shortest possible time. Question for experienced administrators. Who can come across some kind of competent tutorial like learn.javascript.ru only on topics indicated in the tags ??

Answer 1

"As soon as possible" and "learn to administer Linux, mysql, pgsql and telephony" are mutually exclusive paragraphs. Also, "enough experience" doesn't mean anything, so your question is not a question, but a cry to the sky, and everyone will tell you "read the documentation, use google" on every problem.
But in a normal way, an experienced person whom you are helping should already be in place. This will be the fastest, because "learning to administer Linux" and "learning to support Linux in a specific office with a specific infrastructure" are two different things.

Answer 2

Taking into account the fact that on Postgres I have been returning to reading its documentation for more than a year, I think that it is unlikely that a sane "tutorial" can be found. Or it will be a book of simply enchanting volume.
On MySQL - at one time I liked the book, the author (or co-author) of which is a certain "Kuznetsov". It was a pretty good book, in my opinion. But, here it is worth making an amendment - that this book is more about the SQL capabilities of the database than about its deep analysis, fine tuning, etc.
The general theory of relational databases - I think you will find books on this topic without any problems.
Telephony - generally not familiar with the topic and was not particularly interested, I'll skip it.
Linux administration - it is very unlikely that you will find something complete. Firstly, by the fact that this topic pulls a whole chain of literally everything, from the network and network protocols to the kernel mechanisms. Linux is not only a few pieces/dozens/hundreds/... of commands on the command line, it's literally everything, from installing software and configuring a web server to who knows what else. You can easily find one of interest on a specific topic, for example, working with the command line, or setting up the same web server, or setting up iptables for example. But taking into account the fact that more than one book has already been written on iptables alone (the same applies to the command line, the text editor vi и т.д., по всем этим темам есть как минимум одна книга посвященная только ей), представьте себе объём информации по теме "администрирование".

Answer 3

Посмотрите тут:
https://www.youtube.com/user/itsemaev/playlists