[Conda] Error: CondaError — Downloaded bytes did not match Content-Length — How to Fix It

Summary

The Conda error Downloaded bytes did not match Content-Length means the downloaded package file size doesn’t match what the repository server expected. This integrity check prevents Conda from installing incomplete or corrupted packages. The issue is usually caused by unstable internet connections, proxies, or cached partial downloads. Clearing Conda’s cache and retrying typically fixes it.

Context

Conda verifies the size and hash of every downloaded package to ensure data integrity. When the number of bytes actually received doesn’t match the server’s Content-Length header, Conda halts the installation and flags a corruption. The error often arises after interrupted downloads, proxy interference, or outdated cache files in the pkgs/ directory. It’s a safety measure to prevent broken or partial installations that could destabilize environments.

Probable Cause

  • Unstable or interrupted network connection during download.
  • Proxy, VPN, or firewall truncating or buffering package data.
  • Corrupted or incomplete cached file in Conda’s pkgs/ folder.
  • Outdated Conda version misreporting file size or checksum.
  • Incorrect Content-Length headers from remote mirrors.

Quick Fix

Apply the following corrective actions step by step:

  1. Clean Conda’s cache and temporary data:
conda clean --all
  1. Retry your installation or update:
conda install
  1. If the issue persists, switch to a reliable channel like conda-forge:
conda install -c conda-forge
  1. Check proxy or VPN configuration — disable them temporarily or set properly:
conda config --set proxy_servers.http  http://user:pass@proxy:port
conda config --set proxy_servers.https https://user:pass@proxy:port
  1. Increase timeout thresholds for slow or unstable networks:
conda config --set remote_connect_timeout_secs 60
conda config --set remote_read_timeout_secs 120
  1. Update Conda to refresh the downloader and checksum validation logic:
conda update conda

Full Example

Suppose you run: 

conda install pandas

and receive: 

CondaError: Downloaded bytes did not match Content-Length

This indicates a mismatch between expected and received bytes. You clean the cache: 

conda clean --all

Retrying the installation resolves the issue: 

conda install pandas

If you’re behind a proxy and the error persists, setting proper proxy values and increasing timeouts ensures complete downloads: 

conda config --set remote_connect_timeout_secs 90
conda config --set remote_read_timeout_secs 180

Pitfalls & Debug

  • Symptom: Cache cleaned but error repeats → Fix: Delete ~/.conda/pkgs/ or C:\Users\\Anaconda3\pkgs\ manually.
  • Symptom: Works on one network but not another → Fix: Disable proxy/VPN or test using a wired connection.
  • Symptom: Frequent timeouts on large packages → Fix: Increase remote_read_timeout_secs and reduce simultaneous requests.
  • Symptom: Repeated errors after switching channels → Fix: Update Conda to the latest version.
  • Symptom: MD5 or EOF-related CondaError → Fix: Indicates the same corruption class; cleaning cache resolves it.

Validation & Next Steps

After cleaning and reinstalling, verify Conda downloaded fresh package files: 

ls ~/.conda/pkgs/

Ensure package installation now completes without checksum errors. If you face frequent mismatches, consider using local mirrors, stable wired connections, or configuring Conda for fewer parallel downloads.

Sources

Anaconda Documentation — Troubleshooting Conda downloads
Stack Overflow — “CondaError: Downloaded bytes did not match Content-Length” threads
conda-forge Wiki — network reliability and caching recommendations
Anaconda Community Discussions — checksum and timeout debugging cases

Labels: Tool/Conda, OS/Windows-macOS-Linux, Topic/Network-Download