gfs2gfs: 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/gfs2gfs - from package: gerris-mpi
/usr/bin/gfs2gfs - from package: gerris

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

Error in other languages:
gfs2gfs: bevel nie gevind nie
gfs2gfs: comandă negăsită
gfs2gfs: comando não encontrado
gfs2gfs: commande introuvable
gfs2gfs: command not found
gfs2gfs: käsku ei ole
gfs2gfs: không tìm thấy lệnh
gfs2gfs: komanda nerasta
gfs2gfs: Kommando nicht gefunden.
gfs2gfs: kommandot finns inte
gfs2gfs: komut yok
gfs2gfs: nie znaleziono polecenia
gfs2gfs: níor aimsíodh an t-ordú
gfs2gfs: no se encontró la orden
gfs2gfs: no s'ha trobat l'ordre
gfs2gfs: opdracht niet gevonden
gfs2gfs: parancs nem található
gfs2gfs: perintah tidak ditemukan
gfs2gfs: príkaz nenájdený
gfs2gfs: příkaz nenalezen
gfs2gfs: команда не найдена
gfs2gfs: командата не е открита
gfs2gfs: 命令找不到
gfs2gfs: コマンドが見つかりません