free: 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/free - from package: procps

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

On Debian possible default full paths are:

/usr/bin/free - from package: procps

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

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