This displays the number of open connections to port 80 on a server, dumping the ip address/connection count pairs in ascending order.
netstat -anlp | grep :80 | awk '{print $5}' | awk -F: '{print $1}' | sort | uniq -c | sort -n
This can be useful in combination with grep1 searches performed on
httpd fullstatus
to determine if a DOS attack is being performed on a server.
Restarting httpd while trying to alleviate high load on one of the servers I manage, I was recently presented with the following error
(28)No space left on device: Couldn't create accept lock
After some research I found running the following command1
ipcs -s
showed there were a bunch of semaphores hanging around even though apache had been stopped normally via
service httpd restart
Similar to the code snippet mentioned by Major over at RackerHacker, the following command clears out those semaphores, letting httpd start up without a problem
ipcs -s | grep nobody | perl -e 'while (<STDIN>) { @a=split(/\s+/); print `ipcrm sem $a[1]`}'
