netdomjoin-gui: 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/sbin/netdomjoin-gui - from package: samba-domainjoin-gui

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