qsynth: 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/qsynth - from package: qsynth

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

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