pg_upgradecluster: 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/pg_upgradecluster - from package: postgresql-common

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

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