xvkbd: 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/xvkbd - from package: xvkbd

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

On Debian possible default full paths are:

/usr/bin/xvkbd - from package: xvkbd

You may install the required package with command apt-get install {package}

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