qssign: 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/qssign - from package: libapache2-mod-qos

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

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