mdb_load: 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/mdb_load - from package: lmdb

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

On Debian possible default full paths are:

/usr/bin/mdb_load - from package: lmdb-utils

You may install the required package with command apt-get install {package}

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