fai-mirror: 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-mirror - from package: fai-server

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

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