mighty: 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/mighty - from package: mighttpd2

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

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