pbstop: 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/pbstop - from package: pbstop

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

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