mr: 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/mr - from package: mr

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

On Debian possible default full paths are:

/usr/bin/mr - from package: myrepos

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

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