pmlogger_merge: 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/libexec/pcp/bin/pmlogger_merge - from package: pcp

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

On Debian possible default full paths are:

/usr/lib/pcp/bin/pmlogger_merge - from package: pcp

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

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