ionwarn: 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/ionwarn - from package: ion

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

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