ionice: 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 CentOS possible default full paths are:

/usr/bin/ionice - from package: util-linux-ng

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/ionice - from package: util-linux

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

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