Shulou(Shulou.com)06/02 Report--

In this issue, the editor will bring you about how to check the connection number of ports in Linux. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.

First, check which IP is connected to the local computer.

Netstat-an

2. Check the number of TCP connections

1) count the number of connections at port 80

Netstat-nat | grep-I "80" | wc-l

2) Statistics on the number of httpd protocol connections

Ps-ef | grep httpd | wc-l

3) Statistics of connected data with a status of "established"

Netstat-anp | grep ESTABLISHED | wc-l

4) find out which IP address has the most connections and seal it

Netstat-anp | grep ESTABLISHED | awk {print $5} | awk-F: {print $1} | sort | uniq-c | sort-r + 0nnetstat-anp | grep SYN | awk {print $5} | awk-F: {print $1} | sort | uniq-c | sort-r + 0n

Example:

1. Check the current number of concurrent visits to Apache:

Netstat-anp | grep ESTABLISHED | wc-l

Compare the difference between the numbers of MaxClients in httpd.conf.

2. Check the number of processes:

Ps aux | grep httpd | wc-l

3. You can use the following parameters to view the data

# ps-ef | grep httpd | wc-l1388

Count the number of httpd processes, and a series of requests will start a process to be used on the Apache server.

Indicates that Apache can handle 1388 concurrent requests, and this value Apache can be adjusted automatically according to the load.

# netstat-ant | grep-I "80" | wc-l4341

Netstat-an prints the current network link status of the system, while grep-I "80" is used to extract connections related to port 80, and wc-l counts the number of connections. The final number returned is the total number of requests for all current ports 80.

# netstat-anp | grep ESTABLISHED | wc-l376

Netstat-an prints the current network link status of the system, and grep ESTABLISHED extracts the information about the established connection. Then wc-l statistics. The final number returned is the total number of established connections on all ports 80 currently.

Netstat-ant | | grep ESTABLISHED | wc-

You can view the detailed records of all connections established

Check the number of concurrent requests for Apache and their TCP connection status:

# netstat-n | awk'/ ^ tcp/ {+ + S [$NF]} END {for (an in S) print a, S [a]} 'TIME_WAIT 8947 wait enough time to ensure that the remote TCP receives an acknowledgement of the connection interruption request FIN_WAIT1 15 waits for the remote TCP connection interruption request Or confirmation of a previous connection break request FIN_WAIT2 1 waits for a connection break request from the remote TCP ESTABLISHED 55 represents an open connection SYN_RECV 21 receives and sends a connection request and waits for the other party to confirm the connection request CLOSING 2 does not have any connection status LAST_ACK 4 waits for the confirmation of the original connection break request sent to the remote TCP

Detailed explanation of TCP connection status

LISTEN: listen for connection requests from remote TCP ports

SYN-SENT: wait for a matching connection request after sending a connection request again

SYN-RECEIVED: wait for the other party to confirm the connection request after receiving and sending a connection request

ESTABLISHED: represents an open connection

FIN-WAIT-1: wait for remote TCP connection disruption request, or confirmation of previous connection interruption request

FIN-WAIT-2: waiting for a connection break request from a remote TCP

CLOSE-WAIT: waiting for a connection disconnection request from a local user

CLOSING: wait for the remote TCP to confirm the connection break

LAST-ACK: waits for confirmation of the original connection break request sent to the remote TCP

TIME-WAIT: wait enough time to ensure that the remote TCP receives an acknowledgement of the connection disconnection request

CLOSED: no connection status

SYN_RECV indicates the number of requests waiting to be processed

ESTABLISHED indicates normal data transfer status

TIME_WAIT indicates the number of requests that have been processed and waited for the timeout to end.

4. If you find that there are a large number of TIME_WAIT connections in the system, you can solve the problem by adjusting kernel parameters.

Vim / etc/sysctl.conf

Edit the file and add the following:

Net.ipv4.tcp_syncookies = 1net.ipv4.tcp_tw_reuse = 1net.ipv4.tcp_tw_recycle = 1net.ipv4.tcp_fin_timeout = 30

And then execute

/ sbin/sysctl-p

Let the parameter take effect.

Attach the meaning of the TIME_WAIT status:

Net.ipv4.tcp_syncookies = 1 means that SYN cookies is enabled. When a SYN waiting queue overflow occurs, enable cookies to deal with it to prevent a small number of SYN attacks. The default is 0, which means it is turned off.

Net.ipv4.tcp_tw_reuse = 1 means reuse is turned on. Allow TIME-WAIT sockets to be reused for new TCP connections. Default is 0, which means off.

Net.ipv4.tcp_tw_recycle = 1 means to enable fast recycling of TIME-WAIT sockets in TCP connections. Default is 0, which means disabled.

Net.ipv4.tcp_fin_timeout modifies the system's default TIMEOUT time

5. After the client closes the SOCKET after establishing a TCP/IP connection with the server, the port status of the server connection is TIME_WAIT. Will all socket that perform active shutdown enter the TIME_WAIT state? Is there any situation that causes the actively closed socket to enter the CLOSED state directly?

After sending the last ack, the active shutdown party will enter the TIME_WAIT state to stay in 2MSL (max segment lifetime) time, which is essential to TCP/IP, that is, it cannot be solved. That's how TCP/IP designers designed it.

There are two main reasons:

1. Prevent the packets in the previous connection from reappearing after getting lost, affecting the new connection (after 2MSL, all duplicate packets in the previous connection will disappear)

2. Reliably close the TCP connection in the last ack (fin) sent by the active shutdown party, which may be lost, and the passive party will resend the fin. If the active party is in the CLOSED state, it will respond to the rst instead of the ack. So the active party should be in the TIME_WAIT state, not CLOSED. TIME_WAIT does not take up a lot of resources unless it is attacked. Also, if one party send or recv times out, it will directly enter the CLOSED state.

6. How to set the maximum number of connections for Apache httpd reasonably?

There is a website on hand, the number of people online is increasing, and the access is very slow. It is initially believed that the server resources are insufficient, but after repeated tests, once the connection is connected, it can be opened quickly by constantly clicking on different links on the same page. This phenomenon means that the maximum number of apache connections is full, and new visitors can only wait in line for free links. Once connected, there is no need to reopen the connection within the survival time of keeyalive (KeepAliveTimeout, default is 5 seconds). Therefore, the solution is to increase the maximum number of apache connections.

1. Where can I set it?

Apache 2.24, using the default configuration (FreeBSD does not load custom MPM configuration by default), and the default maximum number of connections is 250

Load the MPM configuration in / usr/local/etc/apache22/httpd.conf (remove the previous comments):

# Server-pool management (MPM specific) Include etc/apache22/extra/httpd-mpm.conf

The visible MPM is configured in / usr/local/etc/apache22/extra/httpd-mpm.conf, but it is divided into many blocks according to the working mode of httpd. Which one is the current working mode of httpd? You can view this by executing apachectl-l:

Compiled in modules: core.c prefork.c http_core.c mod_so.c

See the word prefork, so you can see that the current httpd should be working in prefork mode, and the default configuration of prefork mode is:

StartServers 5 MinSpareServers 5 MaxSpareServers 10 MaxClients 150 MaxRequestsPerChild 0

two。 How much do you want to add?

In theory, of course, the larger the number of connections, the better, but within the capacity of the server, it is related to the server's CPU, memory, bandwidth, and so on.

To view the current number of connections, you can use:

Ps aux | grep httpd | wc-l

Or:

Pgrep httpd | wc-l

Calculate the average amount of memory consumed by httpd:

Ps aux | grep-v grep | awk'/ httpd/ {sum+=$6;n++}; END {print sum/n}'

Because they are mostly static pages, CPU consumption is very low, and each process takes up a small amount of memory, about 200K.

The server has 2 gigabytes of memory, and apart from the service that is normally started, it takes about 500 megabytes (conservatively estimated), and 1.5 gigabytes is available, so in theory, it can support 1.5 gigabytes, 1024 gigabytes, 1024 megabytes, and 200000 = 8053.06368.

With about 8K processes, it should be no problem to support 2W people to access at the same time (it can ensure that 8K people can access quickly, others may have to wait 1 or 2 seconds to connect, and once connected, it will be very smooth)

MaxClients that controls the maximum number of connections, so you can try to configure it to:

StartServers 5 MinSpareServers 5 MaxSpareServers 10 ServerLimit 5500 MaxClients 5000 MaxRequestsPerChild 100

Note that the default maximum of MaxClients is 2500.If you want to exceed this value, you need to explicitly set ServerLimit, and ServerLimit should be placed before MaxClients, and the value should not be less than MaxClients, otherwise you will be prompted when you restart httpd.

After restarting httpd, observe the number of connections by repeatedly executing pgrep httpd | wc-l. You can see that the number of connections does not increase after reaching the MaxClients setting, but visiting the website is also smooth at this time, so there is no need to set a higher value greedily, otherwise, if the website visits increase carelessly in the future, it will run out of server memory. You can gradually adjust it according to the trend of access pressure and changes in memory usage in the future, until you find an optimal setting.

(MaxRequestsPerChild cannot be set to 0, which may cause the server to crash due to memory leak)

The formula for calculating the better maximum:

Apache_max_process_with_good_perfermance < (total_hardware_memory / apache_memory_per_process) * 2apache_max_process = apache_max_process_with_good_perfermance * 1.5

7. Number of real-time detected httpd connections:

Watch-n 1-d "pgrep httpd | wc-l" above is how to check the number of port connections in Linux. If you happen to have similar doubts, please refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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