dpkg-mergechangelogs: 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/dpkg-mergechangelogs - from package: dpkg-dev

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

On Debian possible default full paths are:

/usr/bin/dpkg-mergechangelogs - from package: dpkg-dev

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

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