After upgrading from Ubuntu 18.04 to 20.04, many users encounter a peculiar issue where Nginx crashes during systemctl reload nginx operations. The system logs show segmentation faults (SIGSEGV) in libperl.so, followed by port binding conflicts when attempting to restart the service.

The dmesg output reveals multiple crash patterns:

[31326.529427] traps: nginx[746] general protection fault ip:7f5f8cadc593 sp:7ffd350738d0 error:0 in libperl.so.5.30.0[7f5f8ca74000+166000]
[32103.236557] nginx[26433]: segfault at 3d1 ip 00007efe600ce5c9 sp 00007ffead1b3210 error 4 in libperl.so.5.30.0[7efe60066000+166000]

Key observations from the journal logs:

• Nginx master process exits with SIGSEGV (status=11)
• Systemd kills all worker processes forcibly
• Subsequent restart attempts fail due to port conflicts

During a normal systemctl reload, Nginx should:

1. Start new worker processes with new configuration
2. Gracefully terminate old workers
3. Maintain uninterrupted service

In this failure scenario, the process breaks at step 1, leaving old processes running and ports occupied.

Here's a comprehensive fix combining several approaches:

1. Immediate Workaround

Replace systemctl reload nginx with:

sudo systemctl stop nginx
sudo systemctl start nginx

2. Permanent Fix via Systemd Configuration

Edit /etc/systemd/system/nginx.service.d/override.conf:

[Service]
ExecReload=/bin/kill -HUP $MAINPID
KillMode=process
Restart=on-failure
RestartSec=5s
TimeoutStopSec=5

Then reload systemd:

sudo systemctl daemon-reload

3. Nginx Configuration Enhancement

Add these directives to /etc/nginx/nginx.conf:

worker_shutdown_timeout 10s;
worker_processes auto;
pcre_jit on;

After implementing changes, verify with:

sudo systemctl status nginx
sudo journalctl -u nginx --no-pager -n 50
ss -tulnp | grep nginx

For persistent issues, collect debugging data:

# Install debug symbols
sudo apt-get install nginx-dbg=1.18.0-0ubuntu1 libperl5.30-dbg

# Generate core dump
sudo systemctl set-environment NGINX=1
sudo mkdir -p /var/crash/nginx
sudo sysctl -w kernel.core_pattern="/var/crash/nginx/core.%t.%p"
ulimit -c unlimited

For mission-critical systems, consider:

# Use socket activation
[Unit]
Requires=nginx.socket

[Socket]
ListenStream=80
ListenStream=443

Or implement a health-check wrapper script:

#!/bin/bash
if ! curl -I http://localhost:8080/health &>/dev/null; then
    systemctl restart nginx
fi

---

Since upgrading from Ubuntu 18.04 to 20.04, I've been experiencing random crashes when reloading Nginx through systemd. The service dies with segmentation faults (SIGSEGV) and port binding errors, despite configuration files being valid.

The system logs reveal two distinct but related problems:

# dmesg shows segmentation faults in libperl
[31326.529427] traps: nginx[746] general protection fault ip:7f5f8cadc593 sp:7ffd350738d0 error:0 in libperl.so.5.30.0

# journalctl shows port binding conflicts
Nov 02 05:32:05 fooServer nginx[415078]: nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

After thorough investigation, I found these contributing factors:

1. Perl Module Conflicts

The segmentation faults consistently occur in libperl.so, suggesting an incompatibility between Nginx and Perl modules after the upgrade. This is particularly problematic when using Nginx with Perl scripts or modules.

2. Improper Process Termination

The port binding errors indicate that old Nginx worker processes aren't terminating properly during reload, keeping ports occupied. This creates a race condition during service restart.

Solution 1: Fixing Perl-Related Crashes

First, reinstall Perl-compatible Nginx packages:

sudo apt remove libnginx-mod-http-perl nginx-extras
sudo apt install nginx-full

If you must use Perl with Nginx, try rebuilding the modules:

sudo apt install --reinstall libperl5.30
sudo perl -MCPAN -e 'install("Nginx::Embedded::Perl")'

Solution 2: Reliable Service Reload

Modify the systemd service file (/lib/systemd/system/nginx.service) to ensure proper process termination:

[Service]
ExecReload=/usr/sbin/nginx -s stop && /usr/sbin/nginx
KillMode=process
KillSignal=SIGQUIT
TimeoutStopSec=5

Then reload systemd and Nginx:

sudo systemctl daemon-reload
sudo systemctl restart nginx

Solution 3: Port Binding Verification

Create a pre-reload script to verify port availability:

#!/bin/bash
ports=(80 443 8080)
for port in "${ports[@]}"; do
    if ss -tulpn | grep -q ":$port "; then
        echo "Port $port is in use, killing processes..."
        sudo fuser -k $port/tcp
    fi
done

To avoid future issues:

• Regularly check for Nginx zombie processes: ps aux | grep nginx
• Monitor system logs for Perl-related warnings
• Consider using socket activation for Nginx

After implementing these changes, verify proper operation:

sudo systemctl reload nginx
sudo netstat -tulnp | grep nginx
journalctl -u nginx --since "5 minutes ago"