gfsjoin3D: 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/gfsjoin3D - from package: gerris-mpi
/usr/bin/gfsjoin3D - from package: gerris

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

Error in other languages:
gfsjoin3D: bevel nie gevind nie
gfsjoin3D: comandă negăsită
gfsjoin3D: comando não encontrado
gfsjoin3D: commande introuvable
gfsjoin3D: command not found
gfsjoin3D: käsku ei ole
gfsjoin3D: không tìm thấy lệnh
gfsjoin3D: komanda nerasta
gfsjoin3D: Kommando nicht gefunden.
gfsjoin3D: kommandot finns inte
gfsjoin3D: komut yok
gfsjoin3D: nie znaleziono polecenia
gfsjoin3D: níor aimsíodh an t-ordú
gfsjoin3D: no se encontró la orden
gfsjoin3D: no s'ha trobat l'ordre
gfsjoin3D: opdracht niet gevonden
gfsjoin3D: parancs nem található
gfsjoin3D: perintah tidak ditemukan
gfsjoin3D: príkaz nenájdený
gfsjoin3D: příkaz nenalezen
gfsjoin3D: команда не найдена
gfsjoin3D: командата не е открита
gfsjoin3D: 命令找不到
gfsjoin3D: コマンドが見つかりません