g_trjorder: 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_trjorder - from package: gromacs

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

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