gfs-highlight: 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/gfs-highlight - from package: gerris-mpi
/usr/bin/gfs-highlight - from package: gerris

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

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