gfal2_version: 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 CentOS possible default full paths are:

/usr/bin/gfal2_version - from package: gfal2

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/gfal2_version - from package: gfal2

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

Error in other languages:
gfal2_version: bevel nie gevind nie
gfal2_version: comandă negăsită
gfal2_version: comando não encontrado
gfal2_version: commande introuvable
gfal2_version: command not found
gfal2_version: käsku ei ole
gfal2_version: không tìm thấy lệnh
gfal2_version: komanda nerasta
gfal2_version: Kommando nicht gefunden.
gfal2_version: kommandot finns inte
gfal2_version: komut yok
gfal2_version: nie znaleziono polecenia
gfal2_version: níor aimsíodh an t-ordú
gfal2_version: no se encontró la orden
gfal2_version: no s'ha trobat l'ordre
gfal2_version: opdracht niet gevonden
gfal2_version: parancs nem található
gfal2_version: perintah tidak ditemukan
gfal2_version: príkaz nenájdený
gfal2_version: příkaz nenalezen
gfal2_version: команда не найдена
gfal2_version: командата не е открита
gfal2_version: 命令找不到
gfal2_version: コマンドが見つかりません