qmon: 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/qmon - from package: gridengine-qmon
/usr/share/gridengine/bin/lx26-amd64/qmon - from package: gridengine-qmon

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

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