How to permanently change hostname, centos7?

Question

CentOS

I tried all the commands known to me, it returns on reboot.
The essence of the problem:
I install the program, swears at the hostname:
Startup error: Error: host name "pasys" is not fully qualified, please configure 'host-name' and/or 'domain-suffix'.
I check hostname - displays pasys (the program needs pasys.ru)
tried to change:
hostname pasys.ru
hostnamectl set-hostname pasys.ru manually
changed /etc/hosts and /etc/sysconfig/network
found command scarletctl disable set-hostname - ban on change when I reboot - I enter it gives an error -bash: scarletctl: command not found
I understand the problem in this. How can I prevent the hostname from changing on reboot?

Answer 1

/etc/hostname

Answer 2

this is how chattr +i /etc/hostname helped