grid_monitor.sh: 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/grid_monitor.sh - from package: condor

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

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