memusage: 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/memusage - from package: glibc-utils

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

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