gfal-legacy-register: 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/gfal-legacy-register - from package: gfal2-util

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

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