g_sans: 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 Debian possible default full paths are:

/usr/bin/g_sans - from package: gromacs

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

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