setting ulimit -n with a value more than 1024000

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# 1  
Old 07-26-2009
setting ulimit -n with a value more than 1024000

I would like to set the maximum number or open files per process to be greater than 1024000 (for specific application scalability purpose). I am using RHEL 5.3/Ext4.

%sysctl fs.file-max
fs.file-max = 164766821

I also have added the folloing to /etc/security/limits.conf

* soft nofile 4096000
* hard nofile 4096000

However I am stuck with
ulimit -n <value>

The max value is limited to 1024000.
How can I increase the maximum?

# 2  
Old 07-27-2009
I am thinking that would need a kernel re-compile...

why on earth would you need such large numbers??
# 3  
Old 07-27-2009
Hi Sean,

ulimit -n unlimited

should do..

# 4  
Old 07-27-2009
Originally Posted by ilan
Hi Sean,

ulimit -n unlimited

should do..

this may work but I feel it is asking for problems.

the ulimit is there for a reason, you may find your system becomes unresponsive.
# 5  
Old 07-27-2009
I think the OP is aware of that, however what kind of application will use more than million file descriptors ? If those are the requirements of a software that will work on a standalone system, you better think of clusters, unless the application's overhead / footprint is very small.
# 6  
Old 07-27-2009
Thank you for the replies.

Actually I tried ulimit -n unlimited before and I got the same error as using
ulimit -n <value> when value is greater than 1024000

The application indeed is running on a cluster setting. In the extreme scaling situation the application will need to open a huge number of files concurrently. Will it have scaling issue? This is a part of my intention - to find it out.

I have a feeling that it might need kernel recompilation. Any hint which conf file or .h file needs to be changed?

# 7  
Old 07-30-2009
Could you explain the problem a little more? Maybe some sort of client/server system work better than a cluster. More and smaller file tables instead of one gigantic global file table. Or a method in which fewer files containing more data could be used, are they of fixed size? What kind of data? Altering the kernel may have unexpected consequences, the limit might be that "low" for a reason.
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