pbs_demux: 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/pbs_demux - from package: torque-client
/usr/sbin/pbs_demux - from package: torque-mom

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

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