db_codegen: 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/bin/db_codegen - from package: db4-utils

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