system info

Check Services Versions

dmesg – view hardware
lspci -v – Will give you info about what hardware you are running.
php -v – check php version
mysql -V – Check mysql version
mysql -v -uadmin -p`cat /etc/psa/.psa.shadow` – Check the version of mysql
hostname – shows the host-name of the server
uname -a – tells you about the system

Check the Version of Centos

cat /etc/redhat-release
cat /etc/centos-release
cat /etc/*release*

Check the Version of Plesk

cat /usr/local/psa/version