mdb-hexdump: 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-hexdump - from package: mdbtools

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

On Debian possible default full paths are:

/usr/bin/mdb-hexdump - from package: mdbtools

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

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