nginx client_max_body_size: fix 413 Request Entity Too Large

client_max_body_size is the largest request body nginx accepts, 1 MB by default. A bigger upload is rejected with 413 Request Entity Too Large before it reaches the backend, and the error log says client intended to send too large body. Raise it where uploads happen: client_max_body_size 50m; in the server or location block.

Reproduce and fix

A Node backend counts the bytes it receives; /api/ uses the default limit and /upload/ sets 5 MB:

mkdir -p logs temp
cat > backend.js <<'EOF'
require("http").createServer((req, res) => {
  let n = 0;
  req.on("data", (c) => (n += c.length));
  req.on("end", () => res.end(`backend got ${n} bytes\n`));
}).listen(4211, "127.0.0.1");
setTimeout(() => process.exit(0), 4000);
EOF
cat > nginx.conf <<'EOF'
pid logs/nginx.pid;
events {}
http {
  access_log off;
  server {
    listen 127.0.0.1:4212;
    location /api/    { proxy_pass http://127.0.0.1:4211; }
    location /upload/ { client_max_body_size 5m; proxy_pass http://127.0.0.1:4211; }
  }
}
EOF
node backend.js &
nginx -p . -c nginx.conf -e logs/error.log &
sleep 1
head -c 2000000 /dev/zero > 2mb.bin
curl -s --data-binary @2mb.bin http://127.0.0.1:4212/api/ | grep '<title>'
curl -s --data-binary @2mb.bin http://127.0.0.1:4212/upload/
grep -o 'client intended to send too large body: [0-9]* bytes' logs/error.log
nginx -p . -c nginx.conf -e logs/error.log -s stop

<head><title>413 Request Entity Too Large</title></head>
backend got 2000000 bytes
client intended to send too large body: 2000000 bytes

Where to set it

http {
  client_max_body_size 10m;        # default for every server
  server {
    server_name files.example.com;
    location /upload/ {
      client_max_body_size 200m;   # only for the upload endpoint
    }
  }
}

The most specific block wins: a location value overrides the server value, which overrides http. client_max_body_size 0; disables the check.

Values

Only the suffixes k/K, m/M and g/G exist, and the number must be an integer. A value copied from another tool's syntax fails the configuration test:

mkdir -p logs temp
check() {
  printf 'pid logs/nginx.pid;\nevents {}\nhttp {\n  client_max_body_size %s;\n  server { listen 127.0.0.1:5027; }\n}\n' "$1" > nginx.conf
  echo "--- client_max_body_size $1"
  nginx -p . -c nginx.conf -e stderr -t 2>&1 | sed -E 's/^[0-9/]+ [0-9:]+ \[([a-z]+)\] [0-9#]+: /[\1] /'
}
check 1g
check 10MB

--- client_max_body_size 1g
nginx: the configuration file ./nginx.conf syntax is ok
nginx: configuration file ./nginx.conf test is successful
--- client_max_body_size 10MB
[emerg] "client_max_body_size" directive invalid value in ./nginx.conf:4
nginx: configuration file ./nginx.conf test failed

Pitfalls

• The 413 page may not show in the browser. The nginx docs warn that browsers cannot correctly display this error, so users may report a failed or reset upload rather than a 413. Check the error log for client intended to send too large body.
• Raising it in the wrong block. A client_max_body_size in http is overridden by a smaller value in the server or location that actually handles the upload. nginx -T | grep client_max_body_size lists every value in the merged configuration.
• Forgetting the reload. The new limit applies only after nginx -t && nginx -s reload (see nginx -t).
• Large bodies go to disk. Bodies bigger than client_body_buffer_size (8k or 16k by default, two memory pages) are written to a temporary file in client_body_temp_path, so large upload limits need free disk space there.
• Slow uploads are a different error. If the client stops sending for longer than client_body_timeout (60s by default, measured between two reads), nginx returns 408, not 413.

FAQ