rio: 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/rio - from package: rio

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

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