mode3: 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/mode3 - from package: svgalib

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

Error in other languages:
mode3: bevel nie gevind nie
mode3: comandă negăsită
mode3: comando não encontrado
mode3: commande introuvable
mode3: command not found
mode3: käsku ei ole
mode3: không tìm thấy lệnh
mode3: komanda nerasta
mode3: Kommando nicht gefunden.
mode3: kommandot finns inte
mode3: komut yok
mode3: nie znaleziono polecenia
mode3: níor aimsíodh an t-ordú
mode3: no se encontró la orden
mode3: no s'ha trobat l'ordre
mode3: opdracht niet gevonden
mode3: parancs nem található
mode3: perintah tidak ditemukan
mode3: príkaz nenájdený
mode3: příkaz nenalezen
mode3: команда не найдена
mode3: командата не е открита
mode3: 命令找不到
mode3: コマンドが見つかりません