sudo: 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/sudo - from package: sudo

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

On Debian possible default full paths are:

/usr/bin/sudo - from package: sudo-ldap
/usr/bin/sudo - from package: sudo

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

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