vtysh: 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/vtysh - from package: quagga

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

On Debian possible default full paths are:

/usr/bin/vtysh - from package: quagga

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

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