yindex-g77: 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/yindex-g77 - from package: patchy-g77

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

Error in other languages:
yindex-g77: bevel nie gevind nie
yindex-g77: comandă negăsită
yindex-g77: comando não encontrado
yindex-g77: commande introuvable
yindex-g77: command not found
yindex-g77: käsku ei ole
yindex-g77: không tìm thấy lệnh
yindex-g77: komanda nerasta
yindex-g77: Kommando nicht gefunden.
yindex-g77: kommandot finns inte
yindex-g77: komut yok
yindex-g77: nie znaleziono polecenia
yindex-g77: níor aimsíodh an t-ordú
yindex-g77: no se encontró la orden
yindex-g77: no s'ha trobat l'ordre
yindex-g77: opdracht niet gevonden
yindex-g77: parancs nem található
yindex-g77: perintah tidak ditemukan
yindex-g77: príkaz nenájdený
yindex-g77: příkaz nenalezen
yindex-g77: команда не найдена
yindex-g77: командата не е открита
yindex-g77: 命令找不到
yindex-g77: コマンドが見つかりません