httpd.event: command not found

Have You tried accessing the binary with the full path?

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/sbin/httpd.event - from package: httpd

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