mcheck: 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/mcheck - from package: mtools

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

On Debian possible default full paths are:

/usr/bin/mcheck - from package: mtools

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

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