g_sgangle: 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_sgangle - from package: gromacs

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

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