A tool for analyzing logs after the fact?

Question

System administration

Colleagues.
I need to analyze several gigs of logs from different systems.
How could this be done quickly and for free? I would like to make a selection of errors of the same type and display them in the form of graphs in order to demonstrate them in the future.

Answer 1

A few gigs is not much, grep is enough to get lines with errors.
Through awk, get the necessary data (times and dates?) And drive it into any chart (gnuplot for example).

Answer 2

I use a combination of grep, awk, q , gnuplot.
There is also Logparser for Windows.

Answer 3

ELK?
graylog?