headache: 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/headache - from package: headache

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

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