arm-linux-gnueabihf-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-linux-gnueabihf-size - from package: binutils-arm-linux-gnueabihf

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

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