gfan_leadingterms: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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_leadingterms - from package: gfan

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