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Increase PHP’s limit in the configuration file used by the PHP SAPI that runs the failing code, set a value such as memory_limit = 256M, then restart the service that loads that configuration. The command-line interpreter, Apache, CGI, and PHP-FPM can use different php.ini files, so changing the CLI file will not necessarily change a website.
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Start by identifying the SAPI, change only its active configuration, and verify the result through that same SAPI. This guide covers Ubuntu servers running PHP from the shell, Apache, or PHP-FPM behind Apache or Nginx, including pool-level overrides, service limits, and safe troubleshooting.
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memory_limit is PHP’s per-script ceiling. The PHP Documentation Group defines it as “the maximum amount of memory in bytes that a script is allowed to allocate.” It limits PHP allocations; it does not reserve that amount of RAM for every request and it does not increase the memory available to Ubuntu.
The current PHP manual documents a default of 128M. PHP accepts shorthand units such as M and G. A setting of -1 removes PHP’s own limit, but that is rarely a safe production choice because worker processes can then consume all memory available to the host or service.
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When a script reaches the ceiling, PHP commonly reports an error such as “Allowed memory size exhausted.” The correct fix depends on whether the failing workload is a command-line job, an Apache request, a CGI process, or a PHP-FPM worker.
Identify the PHP SAPI before editing anything
A SAPI (Server Application Programming Interface) is the way PHP is being run. Each SAPI can load a different configuration file and can have a different override hierarchy.
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|---|---|---|---|
| CLI scripts, Composer tasks, cron jobs | php --ini and php -i |
CLI php.ini |
No persistent daemon; run the command again |
| Apache PHP module | A diagnostic request through the affected virtual host | Apache-loaded PHP configuration | Restart or reload Apache |
| CGI under Apache | A diagnostic request through the affected virtual host | CGI PHP configuration | Restart Apache after changing startup configuration |
| PHP-FPM behind Apache or Nginx | A diagnostic request plus the FPM configuration tree | FPM php.ini and possibly a pool file |
Restart or reload the matching FPM service |
Do not infer the web value from a shell command. The website may be using another installed PHP version, another SAPI, or a pool-specific setting.
Check the current CLI value
Run these commands as the user who normally runs the script:
php --ini
php -i | grep -E '^memory_limit'
php -r 'echo ini_get("memory_limit"), PHP_EOL;'php --ini prints the loaded configuration file and any additional scanned directory. The two value checks show the effective setting seen by the CLI interpreter, not by a web request.
If several PHP versions are installed, make sure the php command is the one used by the job. A cron entry can call an absolute binary path, and a deployment script can select a different version than your interactive shell.
Increase the limit for CLI scripts
1. Locate the active CLI file
Read the “Loaded Configuration File” line from php --ini. Ubuntu commonly stores versioned files under a path such as /etc/php/8.3/cli/php.ini, but use the path printed on your machine rather than assuming a version.
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2. Edit the directive
Open the file with an editor that has permission to write system configuration and find the existing memory_limit line. Set one value, for example:
memory_limit = 256MRemove a leading semicolon if the directive is commented out. Keep the unit attached to the number. Use a larger value only when the script genuinely needs it and the host has capacity for concurrent jobs.
3. Run the same checks again
php -i | grep -E '^memory_limit'
php -r 'echo ini_get("memory_limit"), PHP_EOL;'The output should show 256M (or the value you selected). If it does not, you edited a file that this CLI binary does not load, or another configuration file is overriding it.
4. Handle one-off jobs without changing global policy
For a single command, PHP can receive a command-line override:
php -d memory_limit=512M path/to/script.phpThis affects that invocation only. It is useful for a controlled import or maintenance task, but it does not change a website or a separate cron command.
Increase the limit for Apache PHP or CGI
Confirm the web SAPI
Create a temporary file in the document root of the affected virtual host containing:
<?php echo ini_get('memory_limit'); ?>Request it through the same hostname and protocol used by the application. The returned value is the web SAPI’s effective limit. Delete the file immediately after checking; exposing configuration diagnostics on a public site can reveal implementation details.
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A temporary phpinfo() page can show the SAPI and both local and master values, but it is even more revealing. Protect it from public access while testing and remove it as soon as the result is recorded.
Edit the configuration associated with that SAPI
Ubuntu documents Apache-module PHP and CGI as separate deployment choices. Locate the version and SAPI directory used by the web server, then edit that SAPI’s php.ini. A typical versioned Apache path resembles /etc/php/8.3/apache2/php.ini; the actual version and path must match the installation reported by the server.
Set the directive, for example:
memory_limit = 256MRestart Apache
The PHP manual states that php.ini is read when PHP starts. For Apache-module PHP, PHP starts with the web server, so restart or reload Apache after changing the file. A reload may be sufficient for the installed module, while a full restart is the clearest way to ensure every worker has reopened the file. Confirm the service name and status on the host before choosing the command.
Verify through the virtual host
Request the temporary diagnostic page again and compare its value with the CLI output. Different results are expected when CLI and Apache use different SAPIs or PHP versions. Remove the diagnostic file once verification is complete.
Increase the limit for PHP-FPM
PHP-FPM has a master process and pools of workers. It is commonly connected to Nginx or Apache through FastCGI. FPM uses PHP-style configuration syntax in its main configuration and pool files, as documented by the PHP-FPM manual.
1. Find the FPM version and service
Look at the FastCGI socket or upstream configured for the affected virtual host and identify the matching PHP version. On Ubuntu, the service name commonly contains that version and ends in -fpm. Do not restart a different version’s service: the website will continue using the unchanged pool.
2. Edit the FPM php.ini
Use the FPM SAPI directory for the installed version, commonly resembling /etc/php/8.3/fpm/php.ini. Set:
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memory_limit = 256MSave the file and inspect the pool configuration before assuming the global value is authoritative.
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Pool files can contain either of these forms:
php_value[memory_limit] = 256M
php_admin_value[memory_limit] = 256Mphp_admin_value[memory_limit] is authoritative for that pool and cannot be overridden by ini_set() in application code. A pool setting can therefore make the website’s value differ from the global FPM php.ini. Apply the smallest-scope change that solves the problem: a single pool for one application, or the global file only when all FPM applications should receive the new limit.
4. Restart or reload the matching FPM service
FPM reads its master and pool configuration when its processes start. Restart or reload the exact PHP-FPM service serving the virtual host. Existing workers may retain the old value until they are replaced, so verify after the service operation completes and check the service status if it fails to start.
5. Verify through the real application path
Use the temporary ini_get('memory_limit') page through the affected virtual host, or log the value from a protected administrative route. Testing through Nginx, Apache, the correct hostname, and the correct PHP-FPM socket matters: a different virtual host can point to another pool.
Per-directory and application-level settings
Some SAPIs permit a per-directory mechanism such as a .user.ini file, and some applications can call ini_set('memory_limit', '256M'). These methods are appropriate only when the SAPI and hosting control plane allow them.
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- Use a per-directory or application setting when only one site or directory needs more memory.
- Do not expect
ini_set()to defeat an FPMphp_admin_value[memory_limit]setting. - Application changes affect requests after the setting is read; they do not change CLI jobs or other pools.
- After changing a per-directory file, verify through the same virtual host and account that runs the application.
If the host is managed, a control panel or service policy may rewrite the value. In that case, the panel’s PHP settings or the provider’s documented mechanism is the authoritative place to change it.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Choose a value without exhausting the server
A higher per-process ceiling can increase total memory pressure when several workers run concurrently. PHP’s setting is not a reservation, but a workload that approaches the ceiling can consume that much memory. Account for PHP-FPM children, Apache workers, the database, queues, caches, the operating system, and any other services before raising the limit.
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| Situation | Reasonable approach | Risk to check |
|---|---|---|
| A single CLI import fails near the default | Use a command-line -d memory_limit=... override or raise only the CLI file |
Scheduled jobs may run concurrently and multiply usage |
| One web application needs larger uploads or image processing | Raise the application or FPM pool value rather than every PHP site | More simultaneous workers can consume the host’s available memory |
| Several applications routinely need large allocations | Review worker counts and host capacity before making a global increase | System-wide contention can slow or terminate unrelated services |
You are considering -1 |
Use it only for tightly controlled diagnostics or jobs with an independent cap | A runaway request can consume all memory available to the service |
Raising the directive does not create RAM or swap. If the workload genuinely requires more concurrent memory, increase the host’s available capacity or reduce concurrency as well as adjusting PHP.
When Ubuntu or systemd stops the process anyway
Even when PHP accepts a larger memory_limit, the service can be constrained by systemd or another cgroup. Ubuntu documents MemoryHigh as a throttling control and MemoryMax as an absolute unit limit. If a unit cannot contain its memory use below MemoryMax, the unit’s out-of-memory killer can be invoked.
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Why changing php.ini appears not to work
You edited the wrong SAPI file
This is the most common cause. php --ini reports the CLI file only. A browser request may use Apache-module PHP, CGI, or FPM with another version and another directory. Compare a CLI check with a diagnostic request made through the real virtual host.
The service was not restarted or reloaded
The PHP manual says configuration is read when PHP starts. Restart or reload Apache after an Apache-side change, and restart or reload the matching FPM service after an FPM or pool change. Confirm that the operation succeeded rather than assuming the command completed.
An FPM pool overrides the global value
Search the pool configuration for php_admin_value[memory_limit] and php_value[memory_limit]. The pool value is the one the request receives; an administrative value cannot be replaced from application code.
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A different virtual host or PHP version is serving the request
Test through the exact hostname, URL scheme, and site that fails. Check the FastCGI socket or Apache module selected for that site. A successful test on a default virtual host does not prove that the production site uses the same SAPI.
The operating system or cgroup is the real limit
Inspect systemd and container limits when the process is killed rather than reporting a PHP memory error. MemoryHigh can throttle a unit; MemoryMax can terminate it through the unit’s out-of-memory handling.
The requested value exceeds practical capacity
A syntactically accepted value can still be unsafe. If multiple workers each approach the new ceiling, available RAM can disappear quickly. Reduce concurrency, process data in smaller batches, or add capacity instead of repeatedly increasing the directive.
Quick Recap
A repeatable verification checklist
- Identify the failing path: shell, cron, Apache, CGI, or PHP-FPM.
- For CLI, run
php --iniand record the loaded file. - Read the effective CLI value with
php -i | grep -E '^memory_limit'orphp -r 'echo ini_get("memory_limit"), PHP_EOL;'. - For web traffic, create a temporary protected page that prints
ini_get('memory_limit'), request it through the affected virtual host, and remove it immediately. - Edit the configuration belonging to that SAPI and set a qualified value such as
256M. - Inspect FPM pool files for
php_valueandphp_admin_valueoverrides. - Restart or reload the owning Apache or PHP-FPM service.
- Repeat the check through the same path that originally failed.
- Check host and systemd/cgroup memory limits if PHP still fails or the process is killed.
Practical decision guide
| Question | Action |
|---|---|
| Does only a terminal command fail? | Change the CLI configuration or use a one-command -d override. |
| Does a site served directly by Apache fail? | Inspect the web SAPI, edit its Apache/CGI configuration, and restart Apache. |
| Does a site behind Nginx or Apache use FastCGI? | Edit the matching FPM configuration, inspect its pool, and reload the matching FPM service. |
| Does one application need more memory than its neighbors? | Prefer an application or pool-level setting when the SAPI permits it. |
| Does the value look correct but the service still die? | Investigate systemd/cgroup limits and total host capacity. |
Security and maintenance notes
- Delete temporary
phpinfo()and diagnostic pages immediately after testing. - Record which PHP version, SAPI, virtual host, and configuration file were changed; this prevents later edits to the wrong file.
- Keep the value as low as the workload permits and revisit it after application updates.
- When several jobs run together, measure peak service memory rather than judging safety from one successful request.
- Do not use
-1as a substitute for diagnosing an oversized query, unbounded loop, image operation, or batch process.
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