xfmountdev4: 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/xfmountdev4 - from package: xfce-utils

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

Error in other languages:
xfmountdev4: bevel nie gevind nie
xfmountdev4: comandă negăsită
xfmountdev4: comando não encontrado
xfmountdev4: commande introuvable
xfmountdev4: command not found
xfmountdev4: käsku ei ole
xfmountdev4: không tìm thấy lệnh
xfmountdev4: komanda nerasta
xfmountdev4: Kommando nicht gefunden.
xfmountdev4: kommandot finns inte
xfmountdev4: komut yok
xfmountdev4: nie znaleziono polecenia
xfmountdev4: níor aimsíodh an t-ordú
xfmountdev4: no se encontró la orden
xfmountdev4: no s'ha trobat l'ordre
xfmountdev4: opdracht niet gevonden
xfmountdev4: parancs nem található
xfmountdev4: perintah tidak ditemukan
xfmountdev4: príkaz nenájdený
xfmountdev4: příkaz nenalezen
xfmountdev4: команда не найдена
xfmountdev4: командата не е открита
xfmountdev4: 命令找不到
xfmountdev4: コマンドが見つかりません