pbs_mom: 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_mom - from package: torque-mom

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

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