autoconf: 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/autoconf - from package: autoconf

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

On Debian possible default full paths are:

/usr/bin/autoconf - from package: autoconf2.13
/usr/bin/autoconf - from package: autoconf

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

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