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Question: Our server (Solaris) accept a
socket when got a request. Why can we only create 256 sockets? Is it possible to
increase the limit?
Answer: In Solaris and in Unix generally
a socket is actually a file descriptor.
In 2.3 in earlier this requires poking the kernel. In Solaris 2.4+, this can be
accomplished by adding the following lines to
- * set hard limit on file descriptors set rlim_fd_max = 4096
- * set soft limit on file descriptors set rlim_fd_cur = 1024
Raising the soft limit past 256 may confuse certain applications, especially
BCP applications. Raising the limit past 1024 may confuse applications that use
select(). Select() cannot use more than 1024 file descriptors at this time prior
to Solaris 7.
In Solaris 2.6, the RPC code was rewritten to use poll(), which does work with
many more fds than select(). Prior to 2.6, all RPC servers will likely crash and
burn if you increase the fd soft limit past 1024.
Solaris 7 allows upto 65536 fds passed to select; this is the default for 64
bit applications but it requires recompiling with a larger value for FD_SETSIZE
for 32 bit apps.
Programs using stdio or even library calls that use stdio may break when they
have more than 256 files open as that is the stdio limit. Programs using many
filedescriptors should try and reserve a number of low numbered file descriptors
for use by stdio.
The stdio limit is removed for 64 bit applications in Solaris 7;
if you really need more than 256 FILE * in and you can't use Solaris 7+ or need
to run in 32 bits, you can use SFIO from AT&T.
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