diet: 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/diet - from package: dietlibc

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

On Debian possible default full paths are:

/usr/bin/diet - from package: dietlibc-dev
/usr/lib/diet/bin/diet - from package: dietlibc-dev

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

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