Chapter 3: check log files - fix tail command

[mvopalka]

In chapter 3 at the section Check log files the command for printing how many Ansible commands have been executed on each server uses tail instead of cat.

I think the line should be
ansible multi -b -m shell -a "cat /var/log/messages | \ grep ansible-command | wc -l"
instead of
ansible multi -b -m shell -a "tail /var/log/messages | \ grep ansible-command | wc -l"
as description says

This command shows how many ansible commands have been run on each server
(the numbers you get may be different).

and the tail command as I now only print the last 5 lines by default.

The line could also be different according to issue #550

Thank you for awesome book Jeff!