yindexb: 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/yindexb - from package: patchy

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

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