pyrasite-memory-viewer: 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/pyrasite-memory-viewer - from package: pyrasite

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

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