search
HomeOperation and MaintenanceLinux Operation and MaintenanceDetailed introduction on how to check the number of concurrent connections and connection status of Nginx under Linux

Linux Check the number of concurrent connections and connection status of Nginx, etc.

1. Check the number of concurrent requests of the Web server (Nginx Apache) and its TCP connection status:

netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'

Or:

netstat -n | awk '/ ^tcp/ {++state[$NF]} END {for(key in state) print key,"t",state[key]}'The return result is generally as follows:

LAST_ACK 5 (正在等待处理的请求数)
SYN_RECV 30 
ESTABLISHED 1597 (正常数据传输状态) 
FIN_WAIT1 51 
FIN_WAIT2 504 
TIME_WAIT 1057 (处理完毕,等待超时结束的请求数)

Other parameter descriptions:

CLOSED: No connection is active or in progress

LISTEN: The server is waiting for incoming calls

SYN_RECV: A The connection request has arrived, waiting for confirmation

SYN_SENT: The application has started, opening a connection

ESTABLISHED: Normal data transfer status

FIN_WAIT1: The application says it has completed

FIN_WAIT2: The other side has agreed to release

ITMED_WAIT: Wait for all groups to die

CLOSING: Both sides try to close at the same time

TIME_WAIT: Another A release has been initialized on one side

LAST_ACK: Waiting for all packets to die

The three commonly used states are: ESTABLISHED means communicating, TIME_WAIT means active closing, and CLOSE_WAIT means passive closing.

The TCP protocol stipulates that for an established connection, both parties on the network must perform four handshakes to successfully disconnect. If one of these steps is missing, the connection will be in a state of suspended animation and the resources occupied by the connection itself will will not be released. The network server program must manage a large number of connections at the same time, so it is necessary to ensure that useless connections are completely disconnected, otherwise a large number of dead connections will waste a lot of server resources. Among the many TCP states, there are two most noteworthy states: CLOSE_WAIT and TIME_WAIT.

TIME_WAIT

TIME_WAIT is formed when the link is actively closed, waiting for 2MSL time, about 4 minutes. Mainly to prevent the last ACK from being lost. Since TIME_WAIT will take a very long time, the server should try to minimize the number of active connections closed

CLOSE_WAIT

CLOSE_WAIT is formed by passively closing connections. According to the TCP state machine, when the server receives the FIN sent by the client, it sends ACK according to the TCP implementation, so it enters the CLOSE_WAIT state. However, if the server does not execute close(), it cannot migrate from CLOSE_WAIT to LAST_ACK, and there will be many connections in the CLOSE_WAIT state in the system. At this time, it may be that the system is busy processing read and write operations and has not closed the connection that has received FIN. At this time, recv/read has received the FIN connection socket and will return 0.

Why do we need TIME_WAIT state?

Assuming that the final ACK is lost, the server will resend the FIN. The client must maintain TCP status information so that the final ACK can be resent. Otherwise, RST will be sent, resulting in the server thinking that an error has occurred. TCP implementations must reliably terminate both directions of the connection (full duplex closed), and the client must enter the TIME_WAIT state because the client may be faced with retransmitting the final ACK.

Why does the TIME_WAIT state need to remain 2MSL for such a long time?

If the TIME_WAIT state is not maintained long enough (for example, less than 2MSL), the first connection will be terminated normally. A second connection appears with the same associated quintuple, and duplicate packets from the first connection arrive, interfering with the second connection. The TCP implementation must prevent duplicate messages from a certain connection from appearing after the connection is terminated, so keep the TIME_WAIT state long enough (2MSL), and the TCP messages in the corresponding direction of the connection will either be completely responded to or discarded. There is no confusion when establishing a second connection.

Too many sockets in TIME_WAIT and CLOSE_WAIT status

If the server is abnormal, 80% to 90% of the time it will be the following two situations:

1. The server maintains a large number of TIME_WAIT status

2. The server maintains a large number of CLOSE_WAIT status. Simply put, the excessive number of CLOSE_WAIT is caused by improper passive closingconnection processing.

Because the file handle allocated to a user by Linux is limited, and if the two states of TIME_WAIT and CLOSE_WAIT are always maintained, it means that the corresponding number of channels are always occupied, and they are "occupying the pit" No effort", once the upper limit of the number of handles is reached, new requests cannot be processed, followed by a large number of Too Many Open Files exceptions, and Tomcat crashes.

The above is the detailed content of Detailed introduction on how to check the number of concurrent connections and connection status of Nginx under Linux. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Linux: How to Enter Recovery Mode (and Maintenance)Linux: How to Enter Recovery Mode (and Maintenance)Apr 18, 2025 am 12:05 AM

The steps to enter Linux recovery mode are: 1. Restart the system and press the specific key to enter the GRUB menu; 2. Select the option with (recoverymode); 3. Select the operation in the recovery mode menu, such as fsck or root. Recovery mode allows you to start the system in single-user mode, perform file system checks and repairs, edit configuration files, and other operations to help solve system problems.

Linux's Essential Components: Explained for BeginnersLinux's Essential Components: Explained for BeginnersApr 17, 2025 am 12:08 AM

The core components of Linux include the kernel, file system, shell and common tools. 1. The kernel manages hardware resources and provides basic services. 2. The file system organizes and stores data. 3. Shell is the interface for users to interact with the system. 4. Common tools help complete daily tasks.

Linux: A Look at Its Fundamental StructureLinux: A Look at Its Fundamental StructureApr 16, 2025 am 12:01 AM

The basic structure of Linux includes the kernel, file system, and shell. 1) Kernel management hardware resources and use uname-r to view the version. 2) The EXT4 file system supports large files and logs and is created using mkfs.ext4. 3) Shell provides command line interaction such as Bash, and lists files using ls-l.

Linux Operations: System Administration and MaintenanceLinux Operations: System Administration and MaintenanceApr 15, 2025 am 12:10 AM

The key steps in Linux system management and maintenance include: 1) Master the basic knowledge, such as file system structure and user management; 2) Carry out system monitoring and resource management, use top, htop and other tools; 3) Use system logs to troubleshoot, use journalctl and other tools; 4) Write automated scripts and task scheduling, use cron tools; 5) implement security management and protection, configure firewalls through iptables; 6) Carry out performance optimization and best practices, adjust kernel parameters and develop good habits.

Understanding Linux's Maintenance Mode: The EssentialsUnderstanding Linux's Maintenance Mode: The EssentialsApr 14, 2025 am 12:04 AM

Linux maintenance mode is entered by adding init=/bin/bash or single parameters at startup. 1. Enter maintenance mode: Edit the GRUB menu and add startup parameters. 2. Remount the file system to read and write mode: mount-oremount,rw/. 3. Repair the file system: Use the fsck command, such as fsck/dev/sda1. 4. Back up the data and operate with caution to avoid data loss.

How Debian improves Hadoop data processing speedHow Debian improves Hadoop data processing speedApr 13, 2025 am 11:54 AM

This article discusses how to improve Hadoop data processing efficiency on Debian systems. Optimization strategies cover hardware upgrades, operating system parameter adjustments, Hadoop configuration modifications, and the use of efficient algorithms and tools. 1. Hardware resource strengthening ensures that all nodes have consistent hardware configurations, especially paying attention to CPU, memory and network equipment performance. Choosing high-performance hardware components is essential to improve overall processing speed. 2. Operating system tunes file descriptors and network connections: Modify the /etc/security/limits.conf file to increase the upper limit of file descriptors and network connections allowed to be opened at the same time by the system. JVM parameter adjustment: Adjust in hadoop-env.sh file

How to learn Debian syslogHow to learn Debian syslogApr 13, 2025 am 11:51 AM

This guide will guide you to learn how to use Syslog in Debian systems. Syslog is a key service in Linux systems for logging system and application log messages. It helps administrators monitor and analyze system activity to quickly identify and resolve problems. 1. Basic knowledge of Syslog The core functions of Syslog include: centrally collecting and managing log messages; supporting multiple log output formats and target locations (such as files or networks); providing real-time log viewing and filtering functions. 2. Install and configure Syslog (using Rsyslog) The Debian system uses Rsyslog by default. You can install it with the following command: sudoaptupdatesud

How to choose Hadoop version in DebianHow to choose Hadoop version in DebianApr 13, 2025 am 11:48 AM

When choosing a Hadoop version suitable for Debian system, the following key factors need to be considered: 1. Stability and long-term support: For users who pursue stability and security, it is recommended to choose a Debian stable version, such as Debian11 (Bullseye). This version has been fully tested and has a support cycle of up to five years, which can ensure the stable operation of the system. 2. Package update speed: If you need to use the latest Hadoop features and features, you can consider Debian's unstable version (Sid). However, it should be noted that unstable versions may have compatibility issues and stability risks. 3. Community support and resources: Debian has huge community support, which can provide rich documentation and

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
1 months agoBy尊渡假赌尊渡假赌尊渡假赌
Will R.E.P.O. Have Crossplay?
1 months agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

ZendStudio 13.5.1 Mac

ZendStudio 13.5.1 Mac

Powerful PHP integrated development environment

VSCode Windows 64-bit Download

VSCode Windows 64-bit Download

A free and powerful IDE editor launched by Microsoft

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

SecLists

SecLists

SecLists is the ultimate security tester's companion. It is a collection of various types of lists that are frequently used during security assessments, all in one place. SecLists helps make security testing more efficient and productive by conveniently providing all the lists a security tester might need. List types include usernames, passwords, URLs, fuzzing payloads, sensitive data patterns, web shells, and more. The tester can simply pull this repository onto a new test machine and he will have access to every type of list he needs.