I have on several occasions needed to troubleshoot issues which wound up being problems with linux limiting the number of open files for a given process. This can be an annoying issue to troubleshoot since many programs do not gracefully handle this condition and linux does not provide log information which indicates the situation by default. This really applies to all of the linux process limits, not just open files.

So what do we do about it?

When you google the problem, you will typically find references to running ulimit as the service user to determine what the existing limits are. You will quickly discover, that this doesn’t work. For one thing, most service users don’t have shells. Additionally, as you will see in my next post, many services already have configuration which attempts to set the limits on program startup.

Enter the proc filesystem…

cat /proc/805/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            8388608              unlimited            bytes     
Max core file size        0                    unlimited            bytes     
Max resident set          unlimited            unlimited            bytes     
Max processes             7807                 7807                 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       7807                 7807                 signals   
Max msgqueue size         819200               819200               bytes     
Max nice priority         0                    0                    
Max realtime priority     0                    0                    
Max realtime timeout      unlimited            unlimited            us

805 is the pid of the process you want to check.

Have fun…