g_order: 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/g_order - from package: gromacs

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

On Debian possible default full paths are:

/usr/bin/g_order - from package: gromacs

You may install the required package with command apt-get install {package}

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