How to Fix the "Too Many Open Files" Error

What does it mean?

On Linux, almost everything is a file: real files, network connections and logs. Each running program may only keep a certain number of them open at once. This is the open files limit. If a busy program such as a web server or database hits the limit, it shows "Too many open files". It is like a juggler who can only hold so many balls.

Warning: back up any config file before you change it.

Steps

1. Log in to your server with SSH.
2. Check the current limit for your user:

ulimit -n

A common default is 1024. That is low for a busy site.

3. See how many files a program has open. Replace PID with its process number:

ls /proc/PID/fd | wc -l

This counts the open files for that program.

4. Raise the limit for a session, to test:

ulimit -n 65535

This lasts only until you log out.

5. Make it permanent. Back up and open the limits file:

cp /etc/security/limits.conf /etc/security/limits.conf.bak
nano /etc/security/limits.conf

6. Add these lines at the bottom:

* soft nofile 65535
* hard nofile 65535

Soft is the working limit. Hard is the highest value a user can set. The star means all users.

7. Save the file and log out, then log in again.
8. Check with ulimit -n.

For services started by systemd

Services like Nginx or MySQL ignore limits.conf. Set the limit in the service instead:

1. Run systemctl edit nginx (use your service name).
2. Add:

[Service]
LimitNOFILE=65535

3. Save, then restart the service:

systemctl daemon-reload
systemctl restart nginx

Check the system-wide limit

cat /proc/sys/fs/file-max

This number is the most files the whole server can open.

Quick recap

• Each program can hold a limited number of open files.
• Check with ulimit -n.
• Raise it in limits.conf, or in the systemd service.
• Restart the program and test.