How to solve nginx prompt 500 Internal Server Error

In the case of high concurrent connections, nginx is a good alternative to the apache server. nginx can also be used as a layer 7 load balancing server. According to the test results, nginx 0.6.31 php 5.2.6 (fastcgi) can withstand more than 30,000 concurrent connections, which is equivalent to 10 times that of apache in the same environment.
But many people will get 500 errors when using nginx. According to my usage, a large part of the reason is that the file open handle is too small.
In Linux, use this command to increase the file handle opened by the process.
ulimit -shn 51200
The default is only 1000. When the number of links is small, it is not visible. Using this processing method can effectively prevent 500 errors from occurring.
When I visited the website today, I occasionally encountered a 500 internal server error error page.
After checking the relevant information, I thought it was caused by excessive access and limited system kernel processes.
The answer is as follows:
$ ulimit -n
11095
The program limits only 11095 files to be opened. The ulimit command sets the number of file descriptors that a process of the current user can have.
It seems to be the simulated concurrency number There are too many. You need to adjust the number of concurrent settings in nginx.conf. (My configuration host has 2g of memory and 2.8g of cpu.)

Copy code The code is as follows:

vi /etc/nginx/nginx.conf
events {
worker_connections 1024;
}

Adjust to

Copy code The code is as follows:

events {
worker_connections 10240;
}

The above problem will still occur, use
[root@qimutian nginx]# cat /proc/sys/fs/file-max
8192
The maximum number of files that can be opened in the file system
[root@qimutian nginx]# ulimit -n
1024
The program limit can only open 1024 files
Use [root@qimutian nginx] # ulimit -n 8192 Adjust
or permanently adjust the number of open files by adding it at the end of the startup file /etc/rc.d/rc.local (add fs.file-max=8192 at the end of /etc/sysctl.conf)
ulimit -n 8192
Adjust the number of open files in centos5
Use ulimit -a and find that open files cannot exceed 1024 by default. During the stress test yesterday, a 500 error occurred. Please check
for details. nginx appears 500 internal server error
When I woke up and took a look in the morning, I found that it was adjusted as follows
Method 1 (permanent adjustment)
vi /etc/security/limits.conf
Add at the end of the file ：
* soft nofile 8192
* hard nofile 20480
At the same time, add
fs.file-max=8192
at the end of vi /etc/sysctl.conf and restart, use ulimit -n to view The number is already 8192
Method 2 (temporary use)
Enter ulimit -n 8192 directly in the terminal and press Enter to be ok
500 internal server error Error supplement:
1. The hard disk space is full
Use df -k to check whether the hard disk space is full. Clearing up hard drive space can resolve 500 errors. If the access log is enabled in nginx, it is best to close the access log when it is not needed. The access log takes up a lot of hard disk space.
2. nginx configuration file error
This does not refer to a syntax error. If nginx has a syntax error in the configuration file, it will prompt when it is started. When configuring rewrite, 500 errors may occur if some rules are not handled properly. Please check your rewrite rules carefully. If some variables in the configuration file are set improperly, a 500 error will also occur, such as referencing a variable with no value.
3. If none of the above problems exist, it may be that the number of simulated concurrencies is too much, and you need to adjust the number of concurrency settings in nginx.conf.
The solution is:
1 Open /etc/security/limits .conf file, add two sentences

Copy code The code is as follows:

* soft nofile 65535
* hard nofile 65535

2 Open /etc/ nginx/nginx.conf
Add a line below worker_processes

Copy the code The code is as follows:

worker_rlimit_nofile 65535;

3 Restart nginx and reload Enter the settings

Copy code The code is as follows:

kill -9 `ps -ef | grep php | grep -v grep | awk '{print $2}'`
/ usr/bin/spawn-fcgi -a 127.0.0.1 -p 9000 -c 100 -u www-data -f /usr/bin/php-cgi
killall -hup nginx

Restart and check again In the nginx error log, no 500 error was found.
4. It may be a database problem. I didn’t find any problems in the nginx log and php log. Finally, I found that the database could not be accessed. After the correction, the problem was solved.

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