yyt: 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 Debian possible default full paths are:

/usr/bin/yyt - from package: yiyantang

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

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