mono-fpm: 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/mono-fpm - from package: mono-fpm-server

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

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