qstop: 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/qstop - from package: torque-client

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

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