mergerepo_c: 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/mergerepo_c - from package: createrepo_c

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

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