pmnsmerge: 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/pmnsmerge - 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/pmnsmerge - from package: pcp

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

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