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Date: Fri, 13 Jan 2012 15:06:21 -0800
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Subject: Re: [PHP-DEV] FD_SETSIZE warning?
From: rasmus@lerdorf.com (Rasmus Lerdorf)

On 01/13/2012 02:42 PM, Reindl Harald wrote:
> 
> Am 13.01.2012 17:36, schrieb Rasmus Lerdorf:
>> FD_SETSIZE is a system limit on the number of open files a
>> single process can have. From a bash shell type: ulimit -n and
>> you will probably see this magical 1024 number pop up. This
>> means that the default is 1024 on your system, so raising it in
>> PHP won't actually do anything unless you also raise it on your
>> system. We try to match the limit in order to give you a sensible
>> error message instead of your program just breaking quietly, or
>> with a warning that doesn't tell you that it is due to hitting a
>> system limit.
>> 
>> So, in order to raise this you have to both tell your operating
>> system that you want to allow individual processes to open more
>> than 1024 files each and you have to recompile PHP with this
>> higher limit.
>> 
>> Now, having said that, I don't quite understand why a single PHP
>> cgi process would ever need more than 1024 open files at the same
>> time. What exactly are you doing that needs this many
>> descriptors? Sounds like you have a descriptor leak there
>> somehow.
> 
> on "old" sysv-systems it was easy to raise this number with
> "modern" systemd-units "LimitNOFILE=30000" as example is ONE simple
> line to raise this limit
> 
> it is not the job of PHP try to GUESS system-limits and define them
> on compile-time

It isn't a guess. FD_SETSIZE isn't set by PHP, but all sorts of
underlying things need to know what FD_SETSIZE is in order to work
correctly so unfortunately when you increase it you are going to need
to recompile. This isn't unique to PHP. There are some ways to hack
around this, but they are all ugly.

-Rasmus