auth2db-alert: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/sbin/auth2db-alert - from package: auth2db

You may install the required package with command apt-get install {package}
Error in other languages:
auth2db-alert: bevel nie gevind nie
auth2db-alert: comandă negăsită
auth2db-alert: comando não encontrado
auth2db-alert: commande introuvable
auth2db-alert: command not found
auth2db-alert: käsku ei ole
auth2db-alert: không tìm thấy lệnh
auth2db-alert: komanda nerasta
auth2db-alert: Kommando nicht gefunden.
auth2db-alert: kommandot finns inte
auth2db-alert: komut yok
auth2db-alert: nie znaleziono polecenia
auth2db-alert: níor aimsíodh an t-ordú
auth2db-alert: no se encontró la orden
auth2db-alert: no s'ha trobat l'ordre
auth2db-alert: opdracht niet gevonden
auth2db-alert: parancs nem található
auth2db-alert: perintah tidak ditemukan
auth2db-alert: príkaz nenájdený
auth2db-alert: příkaz nenalezen
auth2db-alert: команда не найдена
auth2db-alert: командата не е открита
auth2db-alert: 命令找不到
auth2db-alert: コマンドが見つかりません