socket

nginx 502 Bad Gateway

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1.0 502 Bad Gateway

nginx 502 Bad Gateway

After the update of Linux on the web server, the website would not open in the browser. Instead the following error was displayed.

502 Bad Gateway
nginx/1.14.0

2.0 Solution

First we check the nginx server.

$ systemctl status nginx
● nginx.service
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Socket Programming using UDP in C

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1.0 Datagram sockets

There are two major types of network sockets, viz. Stream sockets (SOCK_STREAM) and Datagram sockets (SOCK_DGRAM). The socket type defines the semantics of communication between this socket and its remote counterpart. Stream sockets provide full-duplex reliable sequenced data streams.… Read more

Socket Programming using TCP in C

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1.0 Client-server model

Client - Server System

Client server model is a software architecture paradigm prevalent in distributed applications. A server has information resources and processes that provide answers to queries and other services to remote clients over the network. Some of the examples of these services are booking an airline ticket and/or a room in a hotel, sending a file to a client, sending a mail message to another person (client), etc.… Read more

systemd – System and service manager in Linux

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1.0 Introduction

systemd is the newer init system used in most Linux distributions since 2015. The first widely used init system was the System V init process, sysvinit. Ubuntu introduced the Upstart init system with Ubuntu 6.10 in 2006. Ubuntu fully migrated to systemd with Ubuntu 15.04 in 2015.… Read more

ss command in Linux

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1. ss command

The ss command gives the socket statistics. It gives information about the network connections. ss is a replacement for the netstat command.

By default, the ss command gives information about non-listening sockets.

$ ss
Netid  State      Recv-Q Send-Q   Local Address:Port       Peer Address:Port
u_str  ESTAB      0      0                    * 4482                  * 4481
u_str  ESTAB      0      0                    * 4285                  * 3631
...
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