rsync: 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/rsync - from package: rsync

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

On Debian possible default full paths are:

/usr/bin/rsync - from package: rsync

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

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