What is the curl error 52 empty reply from server

Question

I have a cron job setup on one server to run a backup script in PHP that is hosted on another server  The command I ve been using is curl -sS http   www example com backup php  Lately I ve been getting this error when the Cron runs  curl   52  Empty reply from server  If I go to the link directly in my browser the script runs fine and I get my little backup ZIP file

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In my case it was server redirection  curl -L solved my problem

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In my case I was using uwsgi  added the property http-timeout for more then 60 seconds but it was not working because of some extra space and config file was not getting loaded properly

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In my case  curl 7 47 0   it is because I set the header content-length on curl command manually with a value which is calculated by postman  I used postman to generate curl command parameters and copy them to shell   After I delete header content-length  it works normally

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This can happen if curl is asked to do plain HTTP on a server that does HTTPS   Example     curl http   google com 443 curl   52  Empty reply from server

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It can happen when server does not respond due to 100  CPU or Memory utilization   I got this error when I was trying to access sonarqube API and the server was not responding due to full memory utilization

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I ran into this error sporadically and could not understand  Googling did not help  I finally found out  I run a couple of docker containers  among them NGINX and Apache  The command at hand addresses a specific container  running Apache  As it turned out  I also have a cron job doing some heavy lifting at times running on the same container  Depending on the load this cron job puts on this container  it was not able to answer my command in a timely manner  resulting in error 52 empty reply from server or even 502 Bad Gateway  I discovered and verified this by plain curl when I noticed that the process I investigated took less than 2 seconds and all of a sudden I got a 52 error and then a 502 error and then again less than 2 seconds - so it was definitely not my code which was unchanged  Using ps aux within the container I saw the other process running and understood  Actually  I was bothered by 502 Bad Gateway from NGINX with long running jobs and could not fix it with the appropriate parameters  so I finally gave up and switched these things to Apache  That s why I was puzzled even more about these errors  The remedy is simple  I just fired up some more instances of this container with docker service scale and that was it  docker load balances on its own   Well  there is more to this as another example showed  This time I did some repetitious jobs  I found out that after some time I ran out of memory used by PHP which cannot be reclaimed  so the process died  Why  Having more than a dozen containers on a 8GB RAM machine  I initially thought it would be a good idea to limit RAM usage on PHP containers to 50MB  Stupid  I forgot about it  but swarmpit gave me a hint  I call ini set  quot memory limit quot  -1   in the constructor of my class  but that only went as far as those 50MB  So I removed those restrictions from my compose file  Now those containers may use up to 8GB  The process runs with Apache for hours now and it looks like the problem is solved  memory usage rising to well beyond 100MB   Another caveat  To easily get and read debug messages  I started said process in Opera under Windows  That is fine with errors appearing soon  However  if the last one is cared for  quite naturally the process runs and runs and memory usage in the browser builds up  eventually making my local machine unusable  So if that happens  kill this tab and the process keeps running fine

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In case of SSL connections this may be caused by issue in older versions of nginx server that segfault during curl and Safari requests  This bug was fixed around version 1 10 of nginx but there is still a lot of older versions of nginx on the internet    For nginx admins  adding ssl session cache shared SSL 1m  to http block should solve the problem   I m aware that OP was asking for non-SSL case but since this is the top page in goole for  empty reply from server  issue  I m leaving the SSL answer here as I was one of many that was banging my head against the wall with this issue

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you can try this curl -sS  http   www example com backup php  by putting your URL into    that worked for me I don t know the exact reason but I suppose that putting the url into    completes the request to the server or just completes the header request

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Curl gives this error when there is no reply from a server  since it is an error for HTTP not to respond anything to a request   I suspect the problem you have is that there is some piece of network infrastructure  like a  firewall or a proxy  between you and the host in question    Getting this to work  therefore  will require you to discuss the issue with the people responsible for that hardware

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Another common reason for an empty reply is timeout  Check all the hops from where the cron job is running from to your PHP target server  There s probably a device server nginx LB proxy somewhere along the line that terminates the request earlier than you expected  resulting in an empty response

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I ve had this problem before   Figured out I had another application using the same port  3000      Easy way to find this out   In the terminal  type netstat -a -p TCP -n   grep 3000  substitute the port you re using for the  3000     If there is more than one listening  something else is already occupying that port   You should stop that process or change the port for your new process

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It happens when you are trying to access secure Website like Https   I hope you missed  s   Try Changing URL to curl -sS -u  username password  https   www example com backup php

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In my case this was caused by a PHP APC problem   First place to look would be the Apache error logs  if you are using Apache    Hope this helps somebody

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this error also can happen if the server is processing the data  It usually happens to me when I do post some files to REST API websites that have many entries and take long for the records creation and return

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Try this -  Instead of going through cURL  try pinging the site you   re trying to reach with Telnet  The response that your connection attempt returns will be exactly what cURL sees when it tries to connect  but which it unhelpfully obfuscates from you   Now  depending on what what you see here  you might draw one of several conclusions   You   re attempting to connect to a website that   s a name-based virtual host  meaning it cannot be reached via IP address  Something   s gone wrong with the hostname   you may have mistyped something  Note that using GET instead of POST for parameters will give you a more concrete answer   The issue may also be tied to the 100-continue header  Try running curl getinfo  ch  CURLINFO HTTP CODE   and check the result

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My case was due to SSL certificate expiration

[curl] What is the curl error 52 "empty reply from server"?

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