pmexp: 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/pmexp - from package: perl-pmtools

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

On Debian possible default full paths are:

/usr/bin/pmexp - from package: pmtools

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

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