cluster_quality.py: 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/lib/qiime/bin/cluster_quality.py - from package: qiime

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

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