arm-none-eabi-size: 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/arm-none-eabi-size - from package: binutils-arm-none-eabi

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

Error in other languages:
arm-none-eabi-size: bevel nie gevind nie
arm-none-eabi-size: comandă negăsită
arm-none-eabi-size: comando não encontrado
arm-none-eabi-size: commande introuvable
arm-none-eabi-size: command not found
arm-none-eabi-size: käsku ei ole
arm-none-eabi-size: không tìm thấy lệnh
arm-none-eabi-size: komanda nerasta
arm-none-eabi-size: Kommando nicht gefunden.
arm-none-eabi-size: kommandot finns inte
arm-none-eabi-size: komut yok
arm-none-eabi-size: nie znaleziono polecenia
arm-none-eabi-size: níor aimsíodh an t-ordú
arm-none-eabi-size: no se encontró la orden
arm-none-eabi-size: no s'ha trobat l'ordre
arm-none-eabi-size: opdracht niet gevonden
arm-none-eabi-size: parancs nem található
arm-none-eabi-size: perintah tidak ditemukan
arm-none-eabi-size: príkaz nenájdený
arm-none-eabi-size: příkaz nenalezen
arm-none-eabi-size: команда не найдена
arm-none-eabi-size: командата не е открита
arm-none-eabi-size: 命令找不到
arm-none-eabi-size: コマンドが見つかりません