git-back: 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/git-back - from package: git-extras

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

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