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Resolved PHP struggling under heavy load - "failed to prepare the stderr pipe: Too many open files (24)"

Rob6566

New Pleskian
We've noticed that PHP repeatedly gives this error when our server is under heavy load. We've experienced this during peak live traffic, and also load testing on a clone of the server.

In /var/log/plesk-php56-fpm/error.log:
[07-May-2020 05:45:20] ERROR: failed to prepare the stderr pipe: Too many open files (24)
[07-May-2020 05:45:21] ERROR: failed to prepare the stderr pipe: Too many open files (24)
[07-May-2020 05:45:21] ERROR: failed to prepare the stderr pipe: Too many open files (24)
[07-May-2020 05:45:21] ERROR: failed to prepare the stderr pipe: Too many open files (24)
[07-May-2020 05:45:21] ERROR: failed to prepare the stderr pipe: Too many open files (24)
[07-May-2020 05:45:21] ERROR: failed to prepare the stderr pipe: Too many open files (24)

When we see these errors, we get a lot of 504 Gateway Timeouts.

We can see that PHP processes have a file limit of 1024, which seems too low (we've increased it for MySQL/Apache/Nginx, but can't figure out how to increase it for PHP):

In /proc/{php_process}/limits:
Max open files 1024 4096 files

We can't figure out how to increase this.

# ulimit -n
65535

In /etc/security/limits.conf:
* soft nofile 65535
* hard nofile 65535


In /proc/sys/fs/file-max:
250000

In /etc/sysctl.conf:
fs.file-max = 250000

We've restarted the server after making those changes.

Software on the server:
- Plesk 12.5
- Apache 2.4.6
- nginx 1.11.1
- PHP 5.6
- Centos 6
- MySQL (MariaDB) 5.5.60


Any thoughts on increasing PHP's max open files?
 
failed to prepare the stderr pipe: Too many open files (24)
This usually means that Open file descriptor rlimit is exceeded.

To fix the issue create a directory and additional configuration file:

# mkdir /etc/systemd/system/php-fpm.d
# vi /etc/systemd/system/php-fpm.d/override.conf

Add the following in the config file:

[Service]
LimitNOFILE=65536

And restart systemd daemon and the service:

# systemctl daemon-reload
# systemctl restart php-fpm.service
 
Thanks for that fast reply Igor.

I've tried that, but it didn't work:

Code:
# systemctl restart php-fpm.service
Job for php-fpm.service failed because the control process exited with error code. See "systemctl status php-fpm.service" and "journalctl -xe" for details.

Code:
# systemctl status php-fpm.service
php-fpm.service - The PHP FastCGI Process Manager
   Loaded: loaded (/usr/lib/systemd/system/php-fpm.service; disabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Thu 2020-05-07 06:57:22 UTC; 41s ago
  Process: 5688 ExecStart=/usr/sbin/php-fpm --nodaemonize (code=exited, status=78)
 Main PID: 5688 (code=exited, status=78)
May 07 06:57:22 [snip] systemd[1]: Starting The PHP FastCGI Process Manager...
May 07 06:57:22 [snip] php-fpm[5688]: [07-May-2020 06:57:22] ERROR: No pool defined. at least one pool section must be specified in config file
May 07 06:57:22 [snip] php-fpm[5688]: [07-May-2020 06:57:22] ERROR: failed to post process the configuration
May 07 06:57:22 [snip] php-fpm[5688]: [07-May-2020 06:57:22] ERROR: FPM initialization failed
May 07 06:57:22 [snip] systemd[1]: php-fpm.service: main process exited, code=exited, status=78/n/a
May 07 06:57:22 [snip] systemd[1]: Failed to start The PHP FastCGI Process Manager.
May 07 06:57:22 [snip] systemd[1]: Unit php-fpm.service entered failed state.
May 07 06:57:22 [snip] systemd[1]: php-fpm.service failed.


However, if I try to load a PHP page on this server, it works.

I restarted the server after making that change.

When I try looking at /proc/{php_process_id}/limits, I see that max open files is still 1024.
Max open files 1024



We're on PHP 5.6.40 on "FPM Application Served By Apache", using Plesk 12.5.
 
I've tried something else that seems to have worked:
In /opt/plesk/php/5.6/etc/php-fpm.conf, I added:
rlimit_files = 65536
Then restarted PHP
 
Yes, my solution was for OS vendor's PHP.
But you have Plesk PHP 5.x (in fact bad idea to use EOLed version)
 
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