clrf: 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/clrf - from package: mh-book

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

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