ifrename: 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:

/sbin/ifrename - from package: wireless-tools

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

On Debian possible default full paths are:

/sbin/ifrename - from package: ifrename

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

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