display-buttons: 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/display-buttons - from package: gpm

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

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