cowbuilder: 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/sbin/cowbuilder - from package: cowbuilder

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

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