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

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

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