avr-gcc: 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/avr-gcc - from package: avr-gcc

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

On Debian possible default full paths are:

/usr/bin/avr-gcc - from package: gcc-avr

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

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