mydns-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/sbin/mydns-pgsql - from package: mydns-pgsql

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

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