rds-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/rds-stress - from package: rds-tools

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

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