dieharder: 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/dieharder - from package: dieharder

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

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