s3cmd: 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/s3cmd - from package: s3cmd

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

On Debian possible default full paths are:

/usr/bin/s3cmd - from package: s3cmd

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

Error in other languages:
s3cmd: bevel nie gevind nie
s3cmd: comandă negăsită
s3cmd: comando não encontrado
s3cmd: commande introuvable
s3cmd: command not found
s3cmd: käsku ei ole
s3cmd: không tìm thấy lệnh
s3cmd: komanda nerasta
s3cmd: Kommando nicht gefunden.
s3cmd: kommandot finns inte
s3cmd: komut yok
s3cmd: nie znaleziono polecenia
s3cmd: níor aimsíodh an t-ordú
s3cmd: no se encontró la orden
s3cmd: no s'ha trobat l'ordre
s3cmd: opdracht niet gevonden
s3cmd: parancs nem található
s3cmd: perintah tidak ditemukan
s3cmd: príkaz nenájdený
s3cmd: příkaz nenalezen
s3cmd: команда не найдена
s3cmd: командата не е открита
s3cmd: 命令找不到
s3cmd: コマンドが見つかりません