rz: 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/rz - from package: lrzsz

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

On Debian possible default full paths are:

/usr/bin/rz - from package: lrzsz

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

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