memtest-setup: 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/sbin/memtest-setup - from package: memtest86+

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

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