actdiag3: 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/actdiag3 - from package: python3-actdiag

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

Error in other languages:
actdiag3: bevel nie gevind nie
actdiag3: comandă negăsită
actdiag3: comando não encontrado
actdiag3: commande introuvable
actdiag3: command not found
actdiag3: käsku ei ole
actdiag3: không tìm thấy lệnh
actdiag3: komanda nerasta
actdiag3: Kommando nicht gefunden.
actdiag3: kommandot finns inte
actdiag3: komut yok
actdiag3: nie znaleziono polecenia
actdiag3: níor aimsíodh an t-ordú
actdiag3: no se encontró la orden
actdiag3: no s'ha trobat l'ordre
actdiag3: opdracht niet gevonden
actdiag3: parancs nem található
actdiag3: perintah tidak ditemukan
actdiag3: príkaz nenájdený
actdiag3: příkaz nenalezen
actdiag3: команда не найдена
actdiag3: командата не е открита
actdiag3: 命令找不到
actdiag3: コマンドが見つかりません