ionrestart: 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
/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/ionrestart - from package: ion

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