Re: How to increat [sic.] max open files?

Richard B. Johnson (
Thu, 2 Jan 1997 13:38:36 -0500 (EST)

On Thu, 2 Jan 1997, James L. McGill wrote:

> On Thu, 2 Jan 1997, Marko Sepp wrote:
> > >I am trying to increase the maximum number of open files
> > >(currently 256). I use Linux 2.0.0 (slackware 96).
> Er, NO. With as much attention as this issue has had in recent months,
> I am quite surprised that the kernel and libc code have not adopted increased
> filehandle support. There are still people saying that "256 filehandles
> should be enough for anyone." Isn't that attitude phiolosophically flawed,
> especially in the face of the people who do need e.g. this scaling factor?
> We await a canonical solution to the "File Descriptor Max" problem.
> We would like to see "no limit", but a high limit would be welcome.
> The best I have managed to do so far is to say that this appears to
> work, given that I recompile the software listed above.

There needs to be "someplace" to put information about every file descriptor
that might be used when a process is created. In other words, each process
"table" is of fixed length. It therefore seems that each process can only
have a certain number of file descriptors. If you make space available for
more than "normal" (whatever that is), you waste valuable RAM. If we were
not stuck with "FILE *file" stuff in 'C', the maximum number of FD's could
be limited only by the largest positive number that can be described by
an "int" on the platform in use.

This is not true of all operating systems. Some operating systems make
artificial limits, but the physical limit is ONLY the maximum number that
can be stored in an "int". Anyway, your "unlimited" file-handles isn't
possible. Even a long int or a quadword, etc., have limits. This presumes
that such a handle won't be used as an index into a fixed-length table of
some sort.

Therefore, the natural question is:

Now many files SHOULD a process access? If you state "all it wants", then
you need some other kind of operating system. If you state 10,000, I can
show a good reason why you will need 10,001. In other words, there MUST
be some kind of limit.

I think that a task, process, program, etc., that needs more than 100
file handles is improperly written. Keeping that many files open at any
one time will cause file destruction if the system crashes. On the other
hand, opening/reading/writing/closing files in rapid sucession is not
very efficient. A file-handle limit forces a programmer to think about
this and design (rather than just write), the program.

Lets say that you have a "mount daemon" that is going to perform NFS
file system access for thousands of clients on the network. I think
another damon should be created if the first runs out of file-handles.
Each time a daemon's resource capability is exceeded, another is created.

Each time a daemon closes its last file, it expires. Now, you have 100
daemons when you need them and 1 daemon when you only need it.

The same is true of database programs, etc. There must be some kind of
discipline enforced by the operating system or you name it chaos.

Dick Johnson
Richard B. Johnson
Project Engineer
Analogic Corporation
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