Date: Wed, 10 Feb 1999 08:29:29 -0800 (PST) From: John Polstra <jdp@polstra.com> To: dirk.vangulik@jrc.it Cc: hackers@FreeBSD.ORG Subject: Re: My ignorance (lsof shows shared lib's). Message-ID: <199902101629.IAA53619@vashon.polstra.com> In-Reply-To: <36C1ADBF.CE85DF2E@jrc.it>
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In article <36C1ADBF.CE85DF2E@jrc.it>,
Dirk-Willem van Gulik <dirk.vangulik@jrc.it> wrote:
> Forgive me my ignorance; but why would one see open file descriptors
> for the shared libraries; long after (I would) assume that they have
> been read in and used. Is that not a one off thing ?
>
> Dw.
>
> httpsd 11646 nobody txt VREG 0,131077 422937 61527
> /usr/lib/libc.so.3.1
> httpsd 11646 nobody txt VREG 0,131077 13581 92418
> /usr/local/lib/perl5/i386-freebsd/5.00404/auto/IO/IO.so
> httpsd 11646 nobody txt VREG 0,131077 184758 77089
> /usr/local/lib/perl5/site_perl/i386-freebsd/auto/GD/GD.so
> httpsd 11646 nobody txt VREG 0,131077 35724 77016
> /usr/local/lib/perl5/site_perl/i386-freebsd/auto/Storable/Storable.so
> httpsd 11646 nobody txt VREG 0,131077 56514 77052
> /usr/local/lib/perl5/site_perl/i386-freebsd/auto/DBI/DBI.so
> httpsd 11646 nobody txt VREG 0,131077 27887 8150
> /usr/local/lib/perl5/i386-freebsd/5.00404/auto/DB_File/DB_File.so
> httpsd 11646 nobody txt VREG 0,131077 22054 92533
> /usr/local/lib/perl5/site_perl/i386-freebsd/auto/DBMS/DBMS.so
> httpsd 11646 nobody txt VREG 0,131077 133977 38841
> /usr/local/lib/perl5/site_perl/i386-freebsd/auto/XML/Parser/Expat/Expat.so
There aren't open file descriptors for the shared libraries. I
checked the dynamic linker sources just to make sure. It closes the
files as soon as they have been mapped into memory.
The reason lsof sees them is because they're memory mapped. Shared
libraries aren't really "read in and used" all at once. Instead,
they're mapped directly into the address space. Over time, as the
process accesses various pages from the shared libraries, the pages
are demand-loaded from the files by the kernel. Thus the process has
a grip on all the shared library files even though it no longer holds
open file descriptors for them.
John
--
John Polstra jdp@polstra.com
John D. Polstra & Co., Inc. Seattle, Washington USA
"Nobody ever went broke underestimating the taste of the American public."
-- H. L. Mencken
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