DDoS
To display how many http connections are open at the moment, enter:
netstat | grep http | wc -l
also
netstat -ntu | awk '{print $5}' | cut -d: -f1 | sort | uniq -c | sort -n
To test your server for vulnerability, you can use Backbox Linux, it has a various testing tools preinstalled.
For example, to test your domain for resistance to DDoS attacks you can use slowhttptest which is in Backbox installation. Example command:
slowhttptest -c 1000 -B -g -o output-file-name -i 100 -r 300 -s 10240 -u http://www.example.com/url/page.html -x 20
Now here are detailed options:
-a start start value of ranges-specifier for range header test -b bytes limit of range-specifier for range header test -c number of connections limited to 1024 -H, B, or R specify to slow down in headers section or in message body. -R enables range test -g generate statistics in CSV and HTML formats, pattern is slow_xxx.csv/html, where xxx is the time and date -i seconds interval between follow up data in seconds, per connection -l seconds test duration in seconds -o file custom output file path and/or name, effective if -g is specified -r connections per second connection rate -s bytes value of Content-Length header, if -B specified -t verb custom verb to use -u URL target URL, the same format you type in browser, e.g https://host:port/ -v level verbosity level of log 0-4 -x bytes max length of follow up data