mock: 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/mock - from package: mock
/usr/sbin/mock - from package: mock

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

On Debian possible default full paths are:

/usr/bin/mock - from package: mock
/usr/sbin/mock - from package: mock

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

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