Max num of concurrent tcp connections && tcp auto tune
 

How do I find the maximum number of concurrent connections (in any state)?

I'm running RHEL5 2.6.18-194.26.1.el5

Also, does tcp auto tune affect the number of concurrent connections or is it mostly used for dynamic buffer size allocation?

Ive seen this question come up a number of times, but I haven't been able to find an answer to it.

IIGC there's no single simple answer: there's hardware limits (Linux auto-tuning the stack on boot looking at available memory), there's kernel compile-time limits (file descriptors), there's ports configured to be used for connections (like net.ipv4.ip_local_port_range) and userland applications may be configured with limits or be compiled with restrictions (epoll vs select?). Even then there's tweaks (like net.ipv4.tcp_tw_reuse) and handing off repetitive requests (proxying) that could help.
* BTW you're not that far behind but for some reason we're at 2.6.18-194.32.1.el5 right now.

Thanks for the info. There's more info here: http://tkj.freeshell.org/unix/max-tcp-connections/