git-annex: 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/git-annex - from package: git-annex

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

On Debian possible default full paths are:

/usr/bin/git-annex - from package: git-annex

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

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