dbmerge: 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/dbmerge - from package: perl-Fsdb

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

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