cmake3: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/cmake3 - from package: cmake3

You may install the required package with command yum install {package}

Error in other languages:
cmake3: bevel nie gevind nie
cmake3: comandă negăsită
cmake3: comando não encontrado
cmake3: commande introuvable
cmake3: command not found
cmake3: käsku ei ole
cmake3: không tìm thấy lệnh
cmake3: komanda nerasta
cmake3: Kommando nicht gefunden.
cmake3: kommandot finns inte
cmake3: komut yok
cmake3: nie znaleziono polecenia
cmake3: níor aimsíodh an t-ordú
cmake3: no se encontró la orden
cmake3: no s'ha trobat l'ordre
cmake3: opdracht niet gevonden
cmake3: parancs nem található
cmake3: perintah tidak ditemukan
cmake3: príkaz nenájdený
cmake3: příkaz nenalezen
cmake3: команда не найдена
cmake3: командата не е открита
cmake3: 命令找不到
cmake3: コマンドが見つかりません