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/hexdump - from package: util-linux-ng

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

On Debian possible default full paths are:

/usr/bin/hexdump - from package: bsdmainutils

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

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