Socket accept - "Too many open files"

Question

I am working on a school project where I had to write a multi-threaded server, and now I am comparing it to apache by running some tests against it. I am using autobench to help with that, but after I run a few tests, or if I give it too high of a rate (around 600+) to make the connections, I get a "Too many open files" error.

After I am done with dealing with request, I always do a close() on the socket. I have tried to use the shutdown() function as well, but nothing seems to help. Any way around this?

Answer 1

There are multiple places where Linux can have limits on the number of file descriptors you are allowed to open.

You can check the following:

cat /proc/sys/fs/file-max 

That will give you the system wide limits of file descriptors.

On the shell level, this will tell you your personal limit:

ulimit -n 

This can be changed in /etc/security/limits.conf - it's the nofile param.

However, if you're closing your sockets correctly, you shouldn't receive this unless you're opening a lot of simulataneous connections. It sounds like something is preventing your sockets from being closed appropriately. I would verify that they are being handled properly.

Answer 2

I had similar problem. Quick solution is :

ulimit -n 4096 

explanation is as follows - each server connection is a file descriptor. In CentOS, Redhat and Fedora, probably others, file user limit is 1024 - no idea why. It can be easily seen when you type: ulimit -n

Note this has no much relation to system max files (/proc/sys/fs/file-max).

In my case it was problem with Redis, so I did:

ulimit -n 4096 redis-server -c xxxx 

in your case instead of redis, you need to start your server.