mrs: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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 Debian possible default full paths are:

/usr/bin/mrs - from package: mrs

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