fai-class: 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/bin/fai-class - from package: fai-client

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

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