pmclient: 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/pmclient - from package: pcp

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

On Debian possible default full paths are:

/usr/bin/pmclient - from package: pcp

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

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