mdb_dump: 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_dump - from package: lmdb

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

On Debian possible default full paths are:

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

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

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