clef: 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/lib/axiom-20140801/bin/clef - from package: axiom
/usr/lib/open-axiom/bin/clef - from package: open-axiom

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

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