gfal_testunlink: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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_testunlink - from package: gfal-doc

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