omnicpp: 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/omnicpp - from package: omniORB-devel

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

On Debian possible default full paths are:

/usr/bin/omnicpp - from package: omniidl

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

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