Terminal Command to find maximum allowed TCP/IP connection on a port in Apache server(CentOS)

Question

Is there any terminal commands to check the maximum allowed number of concurrent TCP/IP connections can be done in Apache server with CentOS??

Answer 1

There is no a single command.

There are configurable limits within Apache httpd itself that govern the number of allowed concurrent incoming TCP connections such as the MaxRequestWorkers <number> directive and/or depending on the selected MPM others, such as ListenBacklog , ServerLimit and ThreadsPerChild.

From the OS level each TCP/IP connection consumes a file descriptor and the number of open file descriptors is both finite and limited.
Limits for Apache httpd are typically set/read with ulimit -n when apache httpd is started or for instance from /etc/security/limits.conf.
The overall OS limit is a kenrel tuneable and set/read with: sysctl fs.nr_open and of interest can also be sysctl net.core.somaxconn.

If you're using a software firewall, i.e. netfiler/iptables/firewalld etc. you may need to look at sysctl net.nf_conntrack_max as well.