gmxdump: 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/gmxdump - from package: gromacs

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

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