ifnames2.59: 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 Debian possible default full paths are:

/usr/bin/ifnames2.59 - from package: autoconf2.59

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

Error in other languages:
ifnames2.59: bevel nie gevind nie
ifnames2.59: comandă negăsită
ifnames2.59: comando não encontrado
ifnames2.59: commande introuvable
ifnames2.59: command not found
ifnames2.59: käsku ei ole
ifnames2.59: không tìm thấy lệnh
ifnames2.59: komanda nerasta
ifnames2.59: Kommando nicht gefunden.
ifnames2.59: kommandot finns inte
ifnames2.59: komut yok
ifnames2.59: nie znaleziono polecenia
ifnames2.59: níor aimsíodh an t-ordú
ifnames2.59: no se encontró la orden
ifnames2.59: no s'ha trobat l'ordre
ifnames2.59: opdracht niet gevonden
ifnames2.59: parancs nem található
ifnames2.59: perintah tidak ditemukan
ifnames2.59: príkaz nenájdený
ifnames2.59: příkaz nenalezen
ifnames2.59: команда не найдена
ifnames2.59: командата не е открита
ifnames2.59: 命令找不到
ifnames2.59: コマンドが見つかりません