When running Nginx with high concurrency configurations, many administrators encounter the frustrating message:

8096 worker_connections exceed open file resource limit: 1024

This occurs despite having proper configurations in:

• nginx.conf (with worker_connections set high)
• /etc/security/limits.conf (with increased nofile limits)
• /etc/default/nginx (with ULIMIT settings)

1. System-wide File Descriptor Limits

First verify current limits with:

# Check global limits
cat /proc/sys/fs/file-max

# Check user limits
ulimit -n

# Check Nginx process limits
cat /proc/$(cat /var/run/nginx.pid)/limits

2. Permanent System Configuration

Add these settings to /etc/sysctl.conf:

fs.file-max = 200000
fs.nr_open = 200000

Then apply immediately:

sysctl -p

3. Service-Specific Configuration

Edit /lib/systemd/system/nginx.service (or create override):

[Service]
LimitNOFILE=200000
LimitNPROC=200000

Then reload systemd:

systemctl daemon-reload
systemctl restart nginx

4. Nginx-Specific Optimizations

Add these to nginx.conf:

worker_rlimit_nofile 200000;
events {
    worker_connections 8096;
    multi_accept on;
    use epoll;
}

After applying all changes:

# Check Nginx process limits
cat /proc/$(cat /var/run/nginx.pid)/limits | grep 'Max open files'

# Alternative verification
sudo -u nginx bash -c 'ulimit -n'

• Forgetting to restart services after config changes
• Mismatch between systemd and init.d configurations
• Not setting both soft and hard limits in limits.conf
• Overlooking PAM session limits

For Debian/Ubuntu systems, also check /etc/pam.d/common-session and add:

session required pam_limits.so

---

When you see the "worker_connections exceed open file resource limit: 1024" error in Nginx, it means your system's file descriptor limit is conflicting with Nginx's configuration. Even though you've set higher limits in limits.conf, several other factors can still enforce the default 1024 limit.

Here's everything you need to check and configure:

# 1. System-wide limits (already done in your case)
/etc/security/limits.conf:
*               hard    nofile          199680
*               soft    nofile          65535
nginx           hard    nofile          199680
nginx           soft    nofile          65535

# 2. Systemd service override (critical for modern systems)
/etc/systemd/system/nginx.service.d/override.conf:
[Service]
LimitNOFILE=65535

# 3. Nginx startup configuration
/etc/default/nginx:
ULIMIT="-n 65535"

# 4. Kernel-level limits
/etc/sysctl.conf:
fs.file-max = 2097152

On Debian 7 with systemd, you need to create a service override:

sudo mkdir -p /etc/systemd/system/nginx.service.d
sudo nano /etc/systemd/system/nginx.service.d/override.conf

# Add these contents:
[Service]
LimitNOFILE=65535

# Then reload and restart:
sudo systemctl daemon-reload
sudo systemctl restart nginx

After making all changes, verify with:

# Check Nginx worker process limits
cat /proc/$(cat /var/run/nginx.pid)/limits | grep "Max open files"

# Check system-wide limits
ulimit -n

# Check kernel limits
sysctl fs.file-max

For high-traffic servers, consider this optimized setup:

# /etc/sysctl.conf additions
fs.file-max = 500000
fs.nr_open = 500000

# /etc/security/limits.conf
*               soft    nofile          100000
*               hard    nofile          500000
nginx           soft    nofile          100000
nginx           hard    nofile          500000

# Nginx configuration
worker_processes auto;
worker_rlimit_nofile 100000;

events {
    worker_connections 40000;
    multi_accept on;
    use epoll;
}

If the error persists after all configurations:

• Check if you're using SELinux (less common on Debian)
• Verify the nginx user exists and has correct permissions
• Ensure no other security modules are limiting resources
• Check for typos in configuration files