mydnscheck-pgsql: 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/mydnscheck-pgsql - from package: mydns-pgsql

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

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