Nginx – PHP exec “unable to fork” intermittent error on CentOS VPS

centosmemorynginxopensslPHP

Using:

PHP 5.5.10
nginx 1.5.10
Centos 6.5

a xen-based 4GB VPS

My site uses encrypted paypal buttons. This encryption is done by the following code:

$openssl_cmd = "($OPENSSL smime -sign -signer $MY_CERT_FILE -inkey $MY_KEY_FILE " .
               "-outform der -nodetach -binary <<_EOF_\n$data\n_EOF_\n) | " .
               "$OPENSSL smime -encrypt -des3 -binary -outform pem $PAYPAL_CERT_FILE";

exec($openssl_cmd, $output, $error);

A couple of times now (a few days apart) the buttons have started to fail to encode. If I run "service php-fpm restart" then everything is fine again.

This is the error given:

PHP Warning:  exec(): Unable to fork [(/usr/bin/openssl smime -sign 
    -signer /var/www/my-pubcert.pem -inkey /var/www/my-prvkey.pem -outform der 
    -nodetach -binary <datasnipped>) | /usr/bin/openssl smime -encrypt -des3 
    -binary -outform pem /var/www/paypal_cert.pem]

Once it happens it seems to happen constantly until I restart php-fpm.

Any ideas what route I should go down to debug/fix this?

Thanks

Best Answer

Most likely the PHP processes start using a lot of memory at some point (you can check that in top, press M to sort the processes by memory). Try setting "pm.max_requests = 100" or, anyway, a much lower value of what you have now (or, around 100 or so if it is 0, which means infinite).

By the way, a much better approach to your encryption would be to use the PHP OpenSSL library rather than executing the command line interface of OpenSSL.

Edit:

At your request (even if it is partially off-topic), you can find documentation and example code for the 2 OpenSSL functions in PHP here and here. You may need to recompile PHP with OpenSSL support or install the required module (normally it should have it built in).

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