mbadblocks: 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/mbadblocks - from package: mtools

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

On Debian possible default full paths are:

/usr/bin/mbadblocks - from package: mtools

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

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