sixpack: 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/sixpack - from package: emboss

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

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