pmhostname: 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/pmhostname - 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/pmhostname - from package: pcp

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

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