g_genbox: 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_genbox - from package: gromacs

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

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