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I get the following error in my log files every time I try to upload a large file.

a client request body is buffered to a temporary file /var/lib/nginx/body/0000000001

Although the file uploads successfully, I always get the above error.

I increased the client_body_buffer_size to 1000m which is what I expect the largest file uploaded to be. However, this is was just a guess and although I don't get that error anymore I am wondering if this is an appropriate value to set for the client_body_buffer_size?

I would appreciate it if anyone can shed some light on this directive and how it should be used.

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    I have this is not successfully uploaded. – Ben Mar 25 '14 at 16:37
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This is a warning, not an error. That's why it was prefaced with [warn] in the log.

It means that the size of the uploaded file was larger than the in-memory buffer reserved for uploads.

The directive client_body_buffer_size controls the size of that buffer.

If you can afford to have 1GB of RAM always reserved for the occasional file upload, then that's fine. It's a performance optimization to buffer the upload in RAM rather than in a temporary file on disk, though with such large uploads a couple of extra seconds probably doesn't matter much. If most of your uploads are small, then it's probably a waste.

In the end, only you can really make the decision as to what the appropriate size is.

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    Your answer has helped me make a decision. I will lower the value to about 512k to 1m. It's a shame I will get a lot of these warnings. – Abs May 29 '13 at 20:53
  • Because of virtual memory, using a large value won't lead to "1GB of RAM always reserved for the occasional file upload". (No more RAM than it's actually needed for the current upload will be used.) – Kirill Bulygin Jun 2 '18 at 7:38
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    If I set this to 50MB and had 200 people view a page at the same instant, would that take up 10GB of memory, or would the 50MB only be allocated for any users performing a file upload? – Codemonkey Sep 18 '18 at 23:02
  • @Codemonkey This buffer is only used while a request body is being uploaded. Once the upload is complete the memory is free to be used for another request. And as the other commenter pointed out, while an upload is not in progress, no memory is used. So it depends on how many simultaneous uploads you have going on at any given instant. – Michael Hampton Sep 18 '18 at 23:51
  • Often ten, probably never more than 20. 128GB box so I have plenty of memory..! Honestly though, I'd be doing it just to get rid of those [warn] lines in my error log - I should probably just ignore them! – Codemonkey Sep 19 '18 at 1:14
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If you don't want to NginX store the body content in a temporary file, you can set your config. like this:

    client_body_buffer_size     10M;
    client_max_body_size        10M;

If you set both of this configurations at the same max. size (in k, M or G for kB, MB or GB, respectively), you will prevent that NginX creates a temp. file.

For more info: http://nginx.org/en/docs/http/ngx_http_core_module.html#client_body_buffer_size and http://nginx.org/en/docs/http/ngx_http_core_module.html#client_max_body_size

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    But with that config you will also prevent all uploads which are larger than 10 MiB – Josef says Reinstate Monica Feb 16 '17 at 14:55
  • @Josef: Not prevent by any means. It is just that the request will need to be buffered to disk, and you will get the warning. Check the accepted answer. – OmarOthman Mar 7 '17 at 15:18
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    @OmarOthman, Josef is right because of the client_max_body_size parameter. See the info on this link: client_max_body_size doc.: Sets the maximum allowed size of the client request body, specified in the “Content-Length” request header field. If the size in a request exceeds the configured value, the 413 (Request Entity Too Large) error is returned to the client. Please be aware that browsers cannot correctly display this error. Setting size to 0 disables checking of client request body size. – eddy85br Mar 7 '17 at 19:07
  • Hey, Do you know why my nginx is writing to temporay file when settting proxy_buffering off; and then location / {proxy_pass ...; }? How do I disable writing to temporary file alltogether? – Sudip Bhattarai Feb 25 at 16:28
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    @eddy85br Thanks. I had to do proxy_buffering off; to turn off response buffering and proxy_request_buffering off; to turn off request buffering. The proxy_cache off; is about caching response and it's turned off by default. :nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_cache – Sudip Bhattarai Feb 27 at 17:57

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