celerybeat: 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 CentOS possible default full paths are:

/usr/bin/celerybeat - from package: python-celery

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/celerybeat - from package: python-celery-common

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

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