upgrade-db: 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/cyrus/bin/upgrade-db - from package: cyrus-common

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

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