file-rename: 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/file-rename - from package: rename

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

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