new-memtest-pkg: 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:

/sbin/new-memtest-pkg - from package: memtest86+

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

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