rename.ul: 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/rename.ul - from package: util-linux

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

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