flexpart.gfs: 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/flexpart.gfs - from package: flexpart

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

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