mrd: 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/mrd - from package: mtools

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

On Debian possible default full paths are:

/usr/bin/mrd - from package: mtools

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

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