gfan_buchberger: 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/gfan_buchberger - from package: gfan

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

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