celery: 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/celery - from package: python-celery-common

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

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