gl-mirror-shell: 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/gl-mirror-shell - from package: gitolite

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

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