failed to open stream too many open files - php 1024 maximum limit - Redhat - why isn't new limit working?

Question

I've got this message while debugging a problem in a PHP program.

• I've already edited the /etc/security/limits.conf and added

*         hard    nofile      500000
*         soft    nofile      500000
root      hard    nofile      500000
root      soft    nofile      500000

as instructed here (https://rtcamp.com/tutorials/linux/increase-open-files-limit/). After that, typing

ulimit -Hn

and

ulimit -Sn

reveals the new limit, 500000.

• I've already edited the /etc/pam.d/common-session file and added the line

session required pam_limits.so

• I've then rebooted the system. My program continues to throw an exception when it tries to open file #1025.

• I got the php process PID (27263) and then did a cat /proc/27263/limits

Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            10485760             unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             95124                95124                processes
Max open files            1024                 4096                 files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       95124                95124                signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us

As you can see, even after setting those system wide configurations, the PHP process still has a 1024 max open files limit.

Why?? How can I change that? Why aren't the system wide settings working for this particular case?

Thank you

Solution

Short answer (for a 500000 limit)

1. Edit /etc/security/limits.conf and add this to the end of the file:

*         hard    nofile      500000
*         soft    nofile      500000
root      hard    nofile      500000
root      soft    nofile      500000

2. Edit file /etc/sysconfig/httpd and add at the end add:

ulimit -n 500000

3. Reboot (don't know if it is absolutely necessary)

4. Bingo!

Long answer

Turns out that, according to Make ulimits work with start-stop-daemon and this Red Hat mailing list discussion,

limits.conf(5) is the configuration for pam_limits(8), which is activated by the PAM stack according to the configuration in /etc/pam.d. However, start-stop-daemon(8) as launched from an init.d script doesn't pass through the PAM stack, so those kinds of settings are never applied.

Or in simpler terms,

/etc/security/limits.conf applies to logins, and user "apache" isn't logging in.

The solution proposed in the first link is to edit the init.d script, and add the ulimit -n to the end of the script.

However, as can be observed in the second link, if you edit the /etc/init.d/httpd script, a system update can overwrite the file and the changes would go away.

So that's why they suggested here, here and here to edit the /etc/sysconfig/httpd file instead and enter the command there.

That's what I did, and now I got a beautiful cat /proc/pid/limits just how I wanted:

Limit                     Soft Limit           Hard Limit           Units
Max cpu time              unlimited            unlimited            seconds
Max file size             unlimited            unlimited            bytes
Max data size             unlimited            unlimited            bytes
Max stack size            10485760             unlimited            bytes
Max core file size        0                    unlimited            bytes
Max resident set          unlimited            unlimited            bytes
Max processes             500000               500000               processes
Max open files            500000               500000               files
Max locked memory         65536                65536                bytes
Max address space         unlimited            unlimited            bytes
Max file locks            unlimited            unlimited            locks
Max pending signals       95124                95124                signals
Max msgqueue size         819200               819200               bytes
Max nice priority         0                    0
Max realtime priority     0                    0
Max realtime timeout      unlimited            unlimited            us

and the program no longer crashes.

By the way, the system is a RHEL Server 6.6.