rmmer: 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 Debian possible default full paths are:

/usr/share/doc/mh-book/examples/mh/bin/rmmer - from package: mh-book

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

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