Debian 8 apt-get Upgrade Fails with “Failed to Fetch … Connection Failed”

As the revWhiteShadow, and maintaining kts personal blog site at revWhiteShadow, we understand the frustration of encountering persistent apt-get upgrade errors on a Debian 8 “Jessie” server, especially when the error message reads “Failed to Fetch … Connection Failed.” This guide provides a comprehensive troubleshooting approach tailored to a CLI-only, home-use server setup, even after apt-get update is successful. We’ll address potential causes ranging from network configuration issues to mirror selection, providing detailed steps to diagnose and resolve the problem.

Understanding the Problem: Connection Failures During apt-get Upgrade

The error “Failed to fetch … Connection failed” specifically indicates that your Debian system is unable to establish a connection with the specified mirror server to download package files. While apt-get update retrieves package lists, apt-get upgrade attempts to download and install the actual package binaries. The fact that the update process succeeds but the upgrade fails suggests a potential issue with the connection during larger file transfers, or a transient network problem that is more pronounced during the upgrade process.

Initial Checks: Isolating the Issue

Before diving into complex solutions, it’s essential to rule out common causes:

Basic Network Connectivity

Ping Test: Execute the ping command to verify basic network connectivity to external hosts. Try pinging Google’s DNS server (ping 8.8.8.8) and a well-known website (ping google.com). Successful pings indicate that your server can reach the internet.
```
ping 8.8.8.8
ping google.com
```
If pings fail, the issue is likely related to your server’s network configuration or internet connection.
DNS Resolution: Ensure your server can resolve domain names to IP addresses. Use the nslookup command to query a domain name.
```
nslookup google.com
```
If DNS resolution fails, check your /etc/resolv.conf file for the correct DNS server addresses. You can manually add public DNS servers like Google’s (8.8.8.8 and 8.8.4.4) or Cloudflare’s (1.1.1.1).

Ruling Out Mirror-Specific Issues

The current /etc/apt/sources.list file contains multiple mirrors. While redundancy is good, it can complicate troubleshooting.

Comment Out Most Mirrors: Temporarily comment out all but one mirror in your /etc/apt/sources.list file. Choose a mirror that is geographically close to you, such as http://mirror.it.ubc.ca/debian. After editing, run apt-get update to refresh the package lists.

# /etc/apt/sources.list (example after editing)
deb http://mirror.it.ubc.ca/debian jessie main
#deb http://mirror.its.dal.ca/debian jessie main
#deb http://debian.mirror.iweb.ca/debian jessie main
#deb http://debian.mirror.rafal.ca/debian jessie main
#deb http://ftp3.nrc.ca/debian jessie main

deb-src http://mirror.it.ubc.ca/debian jessie main
#deb-src http://mirror.its.dal.ca/debian jessie main
#deb-src http://debian.mirror.iweb.ca/debian jessie main
#deb-src http://debian.mirror.rafal.ca/debian jessie main
#deb-src http://ftp3.nrc.ca/debian jessie main

deb http://mirror.it.ubc.ca/debian jessie-updates main
#deb http://mirror.its.dal.ca/debian jessie-updates main
#deb http://debian.mirror.iweb.ca/debian jessie-updates main
#deb http://debian.mirror.rafal.ca/debian jessie-updates main
#deb http://ftp3.nrc.ca/debian jessie-updates main

deb-src http://mirror.it.ubc.ca/debian jessie-updates main
#deb-src http://mirror.its.dal.ca/debian jessie-updates main
#deb-src http://debian.mirror.iweb.ca/debian jessie-updates main
#deb-src http://debian.mirror.rafal.ca/debian jessie-updates main
#deb-src http://ftp3.nrc.ca/debian jessie-updates main

Test Each Mirror Individually: If the upgrade still fails, try uncommenting each mirror one at a time, running apt-get update after each change. This will help isolate whether a specific mirror is consistently causing problems.

Investigating MTU Size Issues

A Maximum Transmission Unit (MTU) mismatch can cause connection problems, especially when dealing with larger packets during downloads. The standard Ethernet MTU is 1500 bytes, but some network configurations may require a lower MTU.

Check Current MTU: Determine your server’s current MTU setting using the ip command. Replace eth0 with the appropriate network interface name if necessary.
```
ip link show eth0 | grep mtu
```
Test with a Smaller MTU: Temporarily reduce the MTU size to 1400 or even 1300 to see if it resolves the connection issues.
```
sudo ip link set eth0 mtu 1400
```
After changing the MTU, attempt the apt-get upgrade again. If it succeeds, the MTU was likely the problem. To make the change permanent, you’ll need to configure it within your network configuration files (usually /etc/network/interfaces or /etc/dhcpcd.conf, depending on your setup).

Example /etc/network/interfaces Configuration:

auto eth0
iface eth0 inet dhcp
    mtu 1400

Firewall Considerations

While you didn’t mention a firewall, it’s prudent to check if one is active and potentially blocking outgoing connections on specific ports.

Check UFW Status (if installed): If you’re using UFW (Uncomplicated Firewall), check its status.
```
sudo ufw status
```
Ensure that outgoing connections on port 80 (HTTP) and port 443 (HTTPS) are allowed. If not, add the necessary rules.
```
sudo ufw allow out 80
sudo ufw allow out 443
sudo ufw enable
```
iptables (if using): If you’re using iptables directly, examine the rules to ensure that outgoing connections are not being blocked. The specifics of checking and modifying iptables rules are beyond the scope of this introductory guide, but there are many resources online. If you are using iptables it is expected you know the basics of using iptables.

Advanced Troubleshooting Steps

If the basic checks don’t resolve the issue, consider these more advanced troubleshooting techniques:

Investigating Potential Package Corruption

While less likely, corrupted package files in the APT cache can sometimes cause upgrade failures.

Clean the APT Cache: Use the apt-get clean command to remove downloaded package files from the APT cache. This forces APT to re-download the packages.
```
sudo apt-get clean
```
Re-acquire Package Lists: Force APT to re-acquire the package lists.
```
sudo apt-get update
```

Analyzing Network Traffic with tcpdump

The tcpdump utility captures network traffic, allowing you to analyze the communication between your server and the mirror servers.

Install tcpdump: If tcpdump is not already installed, install it.
```
sudo apt-get install tcpdump
```
Capture Network Traffic: Capture traffic on port 80 (HTTP) while attempting the apt-get upgrade. Replace eth0 with your network interface.
```
sudo tcpdump -i eth0 port 80 -w capture.pcap
```
After the upgrade fails, stop the tcpdump capture (Ctrl+C).
Analyze the Capture: Use a tool like Wireshark (on your desktop computer) to open the capture.pcap file and analyze the network traffic. Look for TCP resets, retransmissions, or other anomalies that might indicate a network problem. The analysis of this capture file falls outside of this guide.

Investigating DNS issues

While we touched on DNS briefly, let’s explore this further. Some ISPs have DNS servers that are unreliable.

Switch to a Public DNS Server: Edit the /etc/resolv.conf file and replace your ISP’s DNS servers with Google’s Public DNS (8.8.8.8 and 8.8.4.4) or Cloudflare’s DNS (1.1.1.1 and 1.0.0.1).
```
nameserver 8.8.8.8
nameserver 8.8.4.4
```
Alternatively, you can configure your network interface to use these DNS servers directly in your network configuration file.
DNSSEC Issues: Though less common, DNSSEC issues can sometimes cause resolution failures. If you suspect this, you can try temporarily disabling DNSSEC validation (if it’s enabled) to see if it resolves the problem. However, disabling DNSSEC reduces security, so it should only be done for testing purposes.

Addressing the cdimage.debian.org Download Failures

The issue with downloading netinstall images from cdimage.debian.org failing with a “The connection was reset” error strongly suggests a problem with your internet connection or a firewall/proxy that is prematurely closing connections. The fact that your Arch Linux desktop can upgrade packages fine might indicate that the issue is limited to the network configuration of your Debian 8 server, or it might be revealing the true error on your Debian 8 server. Here are potential reasons and solutions to explore:

Conflicting Desktop Configuration

First and foremost, the fact that the desktop computer sometimes fails, strongly suggest there is some configuration problem on your desktop machine. This has not been fully ruled out.

MTU Differences:

If the MTU is different, and the Debian 8 server has an MTU that is too large, this can cause packet fragmentation problems, leading to connection resets, especially with larger downloads. You can compare the MTU settings on your Arch Linux desktop and Debian 8 server.

Temporary Connection Issues:

Intermittent network congestion can cause connection resets, especially during large downloads. The issue might be happening more frequently with your Debian 8 server due to its location or network path. To check, you can use mtr (My Traceroute) to trace the network path and identify potential points of congestion.

Firewall/Proxy Interference:

Even if you don’t have a explicitly configured proxy, your ISP or network administrator might be using transparent proxies or firewalls that interfere with connections, especially to download servers like cdimage.debian.org. This is more likely if you’re on a corporate or institutional network. You may need to contact your ISP or network administrator to investigate.

Server-Side Issues on cdimage.debian.org:

It’s rare, but possible, that the cdimage.debian.org server itself is experiencing temporary issues or is being overloaded. Try downloading the images at a different time or from a different mirror (if available).

Download Managers:

While downloading through the browser, ensure that you are not using any download manager that may be causing fragmentation issues.

Partition Resizing Considerations

You mentioned recently resizing the /home and /var drive partitions. While this might seem unrelated, it’s worth considering if the resizing process somehow affected the underlying filesystem or disk configuration, particularly if you encountered any errors during the process.

Check Disk Space: Ensure that both / (root) and /var partitions have sufficient free space. A full /var partition can prevent APT from downloading and installing packages.
```
df -h
```
Filesystem Integrity: Run a filesystem check on all relevant partitions to ensure there are no errors.
```
sudo fsck -f /dev/sda1  # Replace /dev/sda1 with the actual partition
sudo fsck -f /dev/sda2
```

Contacting Your ISP or Network Administrator

If you’ve exhausted all the troubleshooting steps and are still experiencing connection problems, it might be necessary to contact your ISP or network administrator. They might be able to identify network-level issues or restrictions that are causing the connection failures.

Conclusion

Troubleshooting apt-get upgrade connection failures can be a complex process, but by systematically investigating each potential cause, you can narrow down the source of the problem and implement the appropriate solution. By systematically checking the above options, we hope you will be able to solve your problem.

Debian 8 apt-get upgrade fails with Failed to fetch … Connection failed

Debian 8 apt-get Upgrade Fails with “Failed to Fetch … Connection Failed” #

Understanding the Problem: Connection Failures During apt-get Upgrade #

Initial Checks: Isolating the Issue #

Basic Network Connectivity #

Ruling Out Mirror-Specific Issues #

Investigating MTU Size Issues #

Firewall Considerations #

Advanced Troubleshooting Steps #

Investigating Potential Package Corruption #

Analyzing Network Traffic with tcpdump #

Investigating DNS issues #

Addressing the cdimage.debian.org Download Failures #

Conflicting Desktop Configuration #

MTU Differences: #

Temporary Connection Issues: #

Firewall/Proxy Interference: #

Server-Side Issues on cdimage.debian.org: #

Download Managers: #

Partition Resizing Considerations #

Contacting Your ISP or Network Administrator #

Conclusion #