yyref: 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/yyref - from package: cutils

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

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