MAX limit of file descriptor

[Peter Teoh]

On Sun, Feb 10, 2013 at 8:29 PM,
<michi1 at michaelblizek.twilightparadox.com>wrote:

> Hi!
>
> On 13:10 Sat 09 Feb     , horseriver wrote:
> > hi:)
> >
> >    In one process ,what is the max number of opening file descriptor ?
>
> Type "ulimit -a" in your shell. On my system (debian) the default is 1024.
>

Hi Michael, nice to see u again.

BTW, many of the parameters as reported by ulimit, also has to be taken
with some doubts:

ulimit -a
core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 47543
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 47543
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

the above is for Ubuntu 12.04 with 32-bit kernel (3.2.0) but of course we
know that max file size has a limit - depending on whether it is ext2 or
ext3 or ext4.   cannot remember the exact nos, but general conceptual
level, there is a limit.

even for "CPU time"...it is limited by the underlying bit length of
representation for time.   as usual...i don't know the details :-(, just
concept.   sorry :-(.



>
> >    Can it be set to infinite ?
>
> Maybe, but at least it can be set very high.
>
> >    In network programing ,what is the essential for  the maximum of
> connections
> >    dealed per second
>
> - Use non blocking i/o and epoll(). Do *not* create 1 process/thread for
> each
>   connection and do not use use select().
> - Obviously, the more memory your application uses, the more memory has to
> be
>   put in the server. IIRC, 1 tcp connection uses ~1kb kernel memory.
> - The same applies for cpu time. On the system side, you may want to
> recommend
>   network adaptors which can be switched to polling instead of raising 1
>   interrupt per packet. You should expect to see lots of small packets on
> the
>   network.
>
>         -Michi
> --
> programing a layer 3+4 network protocol for mesh networks
> see http://michaelblizek.twilightparadox.com
>
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-- 
Regards,
Peter Teoh
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