mmdblookup: 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/mmdblookup - from package: libmaxminddb-devel

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

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