gfal-mkdir: 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-mkdir - from package: gfal2-util

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

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