stress: 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/stress - from package: stress

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

On Debian possible default full paths are:

/usr/bin/stress - from package: stress

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

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