adsl-setup: 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/sbin/adsl-setup - from package: rp-pppoe

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

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