ffindex_modify: 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/ffindex_modify - from package: ffindex

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

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