Applicable to:
- Plesk for Linux
Symptoms
-
Domain's PHP handler is set as FPM application served by Apache or FPM application served by nginx at Domains > example.com > PHP Settings.
-
The following message can be found in PHP-FPM error log (
/var/log/php-fpm.logor/var/log/plesk-phpXX-fpm/error.logwhere X is a PHP version):CONFIG_TEXT: WARNING: [pool example.com] server reached max_children setting (5), consider raising it
ERROR: unable to read what child say: Bad file descriptor (9)OR
CONFIG_TEXT: [pool example.com] seems busy (you may need to increase pm.start_servers, or pm.min/max_spare_servers), spawning 8 children, there are 4 idle, and 152 total children
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The website is not accessible with one of the following errors:
PLESK_INFO: 503 Service Temporarily Unavailable
OR
PLESK_INFO: 502 Bad Gateway
OR
PLESK_INFO: 500 Internal Server Error
-
Server performance might be slow.
- The following error can be found in
/var/www/vhosts/system/example.com/logs/proxy_error_logCONFIG_TEXT: [error] 11456#0: *118348 connect() to unix:///var/www/vhosts/system/example.com/php-fpm.sock failed (11: Resource temporarily unavailable) while connecting to upstream, client: 203.0.113.2, server: example.com, request: "GET / HTTP/1.1", upstream: "fastcgi://unix:///var/www/vhosts/system/example.com/php-fpm.sock:", host: "example.com"
Cause
The limit of pm.max_children (PHP-FPM pool parameter) for a website has been reached.
Additionally, pm.start_servers, pm.min_spare_servers and pm.max_spare_servers might need adjusting.
Resolution
For Plesk Onyx 17.5 and newer releases
Starting from Plesk Onyx 17.5.30 Update #32, the PHP-FPM limits can be changed via Plesk:
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In Plesk, go to Domains > example.com > PHP Settings > PHP-FPM Settings.
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Adjust the PHP-FPM settings for a domain.
It is possible to set PHP-FPM settings for multiple domains via a service plan. Check this KB article for details.
For Plesk 12.5 and older releases
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Connect to a Plesk server via SSH.
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Create the file
php.iniin directory/var/www/vhosts/system/example.com/conf/:# touch /var/www/vhosts/system/example.com/conf/php.ini
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Open the file
php.iniin a text editor (for example, "vi" editor) and add the following records:CONFIG_TEXT: [php-fpm-pool-settings]pm.max_children = 40
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Update PHP settings to apply the changes:
# /usr/local/psa/bin/php_settings -u
If the issue persists, increase the value of pm.max_children to a greater value.
Note: In some cases, not optimized application code can cause long living PHP-FPM processes, which is causing limit overuse. In such cases the best practice is to resolve the application code issue instead of raising pm.max_children limit.
Additional Information:
To check if there are other domains affected by exceeded limits, use the following command to parse PHP-FPM error logs:
# grep "server reached max_children setting" /var/log/*php*-fpm/error.log | awk '{print $5}' | sort -n | uniq -c
Comments
10 comments
Great help and tutorial ! Thanks a lot
Possible to apply this setting to all domains with single file editing? I have lots of domains to be configured 1 by 1
@Sharul Hafiz You can check the article mentioned in Additional Information section - https://support.plesk.com/hc/en-us/articles/115001201949
Keep in mind that increasing of pm.max_children parameter for all domains can affect the server performance significantly. It is better to filter only affected domains in /var/log/plesk-phpXX-fpm/error.log file
===
grep "server reached max_children setting" /var/log/plesk-phpXX-fpm/error.log
===
and adjust max_children just for them.
@Nikolay What is the limit of pm.max_children? let say if I have 10GB free ram.
@Sharul
The setting is purely depends on amount of traffic for the website. Try to double the default value (from 5 to 10) and monitor the site for several days.
If the same error appears again, analyze the time period between reaching MaxChildren. In case the time like several minutes, double the value again (from 10 to 20), in case the error appears once a day, just add one more child to the configured value (20 to 21).
Typically, 20 is more than enough for medium-loaded websites.
This line
# grep "server reached max_children setting" /var/log/php-fpm/error.log | awk '{print $5}' | sort -n | uniq -cis wrong, as it should be
# grep "server reached max_children setting" /var/log/plesk-phpXX-fpm/error.log | awk '{print $5}' | sort -n | uniq -cMay you insert
in Additional PHP directives field of PHP Settings page for domain?
Hello Marco,
Both files (/var/log/php-fpm/error.log and /var/log/plesk-phpXX-fpm/error.log) exist on the filesystem. The first is used to store errors from system php-fpm, and the second is used when we are speaking about php-fpm which is provided bu Plesk.
Meanwhile, I have edited the article in this way:
# grep "server reached max_children setting" /var/log/*php*-fpm/error.log | awk '{print $5}' | sort -n | uniq -c
As for the second question, Additional PHP directives field is used to insert configuration directives in /var/www/vhosts/system/example.com/conf/php.ini file (configuration file for php itself), however pm.max_children directive should be added to the configuration file of php-fpm pool (/var/www/vhosts/system/example.com/conf/php.ini).
So, this is two different files. And now Plesk could manage only php settings, but not php fpm pool settings.
If you would like Plesk to manage php fpm pool settings, vote for this feature on Plesk Uservoice portal.
@Konstantin
You provided the same path for both php.ini files and said these were two different files.
Hello @Lars,
Thank you for noticing. Indeed, additional directives are stored in/var/www/vhosts/system/example.com/conf/php.ini and PHP-FPM settings are stored in /opt/plesk/php/X.X/etc/php-fpm.d/example.com.conf.
As it is stated in the article, now it is possible to change PHP-FPM settings in Pleks GUI.
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