File Descriptor Limit

Question

1. We can change the limits by setting the values in the /etc/system file rlim_fd_cur & rlim_fd_max.
2. There is some documentation that states that the mx should never exceed 1024.
3. Question:
a. For Solaris 8 can we ever set the max to be > 1024?
b. If we can, is there another ceiling?
c. Can we redefine FD_SETSIZE in the app that wants to use select() with fds > 1024? Is there any mechanism to do a select() on FDs > 1023?
4. If the process is running at root, does it still have a limit on FDs? Can it then raise it using setrlimit()?
Thnx
Aman

Answer 1

The hard limit is 1024 for number of descriptors.
The man page for limit(1) says that root can
change the hard limits, but if you raise the
limit for fd above 1024 you may encounter kernel
performance or even failure considtions. The number
is a recommendation and emperical based on what a
selection of processors and memory models can
tolerate. You might get more expert info by cross
posting this question to the solaris-OS/kernel
forum. Raising the hard limit might be possible, but
I cannot speak to the risks with much direct
knowledge.
You might want to examine the design of an app that
needs to have more than 1024 files open at once. maybe
there is an alternative design that allows you to
close more file descriptors.