g_genrestr: 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_genrestr - from package: gromacs

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

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