feedvalidator: 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/bin/feedvalidator - from package: python-feedvalidator

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