times the listen queue of a socket overflowed Networking Origin: Network OSI layer 4 · Transport Last updated 5 Nov 2026

Networking: netstat -s: 1523 times the listen queue of a socket overflowed — accept queue full, connections dropped

The application accepts connections slower than they arrive, so the kernel's accept queue overflows.

Exact message you may see times the listen queue of a socket overflowedlisten queue overflowedSYNs to LISTEN sockets droppedlisten queue full
Explore the map of this error Full error map →
Seen on: Linux Networking

Meaning

Backlog is capped by min(listen backlog, net.core.somaxconn). Raise somaxconn and the backlog in the app/server (nginx listen ... backlog=, Node server.listen(port, host, backlog)), and fix whatever makes the app slow to accept() (blocked event loop, too few workers).

Common causes

  • Low somaxconn / application backlog
  • App too slow to accept (blocked event loop/workers)
  • Traffic bursts
  • Single-process server saturated
  • Default 128/511 backlog on a busy host

⚡ Quick fix

  1. Check: nstat -az TcpExtListenOverflows
  2. Raise net.core.somaxconn and the app backlog
  3. Add workers and unblock the accept loop

Detailed fix by platform

Linux

  1. bash
    nstat -az TcpExtListenOverflows TcpExtListenDrops
sudo sysctl -w net.core.somaxconn=4096

How to diagnose

  1. ListenOverflows — Rising?
  2. Backlog — Large enough?
  3. App — Accepting promptly?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

Cannot assign requested address (EADDRNOTAVAIL) — Networking: connect: Cannot assign requested address — ephemeral port range exhausted by TIME_WAIT connections (Networking)Cannot assign request…Connections hang on large transfers (PMTU black hole) — Networking: SSH/HTTPS connects but hangs on large data — path MTU discovery black hole (Networking)Connections hang on l…High TCP retransmissions / packet loss — Networking: netstat -s: segments retransmitted / Wireshark: TCP Retransmission, TCP Dup ACK — packet loss on the path (Networking)High TCP retransmissi…Many sockets in CLOSE_WAIT — Networking: Thousands of sockets in CLOSE_WAIT — the application is not closing its side of the connection (Networking)Many sockets in CLOSE…nc/telnet hangs: firewall DROP vs REJECT — Networking: nc -vz hangs then times out — firewall silently DROPs packets (REJECT would answer "Connection refused") (Networking)nc/telnet hangs: fire…Possible SYN flooding on port 80. Sending cookies. — Networking: TCP: request_sock_TCP: Possible SYN flooding on port 80. Sending cookies. Check SNMP counters. (Networking)Possible SYN flooding…TCP ZeroWindow / TCP Window Full — Networking: Wireshark: TCP ZeroWindow, TCP Window Full — the receiver can't keep up and tells the sender to stop (Networking)TCP ZeroWindow / TCP …upstream timed out — Nginx: upstream timed out (110: Connection timed out) while reading response header from upstream (Nginx / Apache)upstream timed outtimes the…

Explore the map of this error Full error map →

🧠 Still stuck? Analyze your error

Paste the full message, response headers or stack trace — we'll detect the platform and point to the most likely cause.

💬 What worked for others

No tips yet — did something else fix this for you?

Share what worked for you

Tips are checked by an editor before they appear. Links are removed.