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From: Andreas Moroder on 5 Aug 2010 06:03
Hello,

today we hade big problem with our server. We discovered that the reason
were missing filehandles. I looked at /proc/sys/fs/file-nr and
discovered that the limit of 131070 used filehandles was reached.

Can anyone please tell me how such a big number of used filehandles can
be reached while lsof | wc -l tells me that there are "only " 48110 open
files ?

I changed file-max to 180000, but this can not be the solution. Is there
a way to get back the "lost" filehandles ?

Thanks
Andreas
From: John Reiser on 5 Aug 2010 12:07
> the limit of 131070 used filehandles was reached.
>
> Can anyone please tell me how such a big number of used filehandles can
> be reached while lsof | wc -l tells me that there are "only " 48110 open
> files ?

fork() increases the number of open handles [file descriptors] but not
the number of open files [inodes]. pipe() creates 2 descriptors but only
one file. open() the same existing file N times [for read only: O_RDONLY]
creates N descriptors for just one file.

> I changed file-max to 180000, but this can not be the solution. Is there
> a way to get back the "lost" filehandles ?

close() them. Find the process, nest of processes, or even unrelated processes
that have many open descriptors, and kill those processes.
See also O_CLOEXEC <fcntl.h>, and the "<&-" shell syntax. Many shell commands
(especially user-written programs) do not use stdin, yet inherit an open stdin
from their parent, thus creating another file descriptor for the same stdin
(which may be /dev/ttyN, etc.)

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