zlibc.3

zlib压缩原码

'\" t
.TH uncompress.so 3 27mar1999 ZLIBC ZLIBC
'\" t
.de TQ
.br
.ns
.TP \\$1
..

.tr \(is'
.tr \(if`
.tr \(pd"

.ds St Zlibc
.oh '\\*(St''%'
.eh '%''\\*(St'
.PP
.SH Name
zlibc - transparently access compressed files.
.PP
.SH Introduction
.PP
The zlibc package allows transparent on the fly uncompression of gzipped
files.  Your programs will be able to access any compressed file, just
as if they were uncompressed.  Zlibc will transparently uncompresses the
data from these files as soon as they are read, just as a compressed
filesystem would do.  No kernel patch, no recompilation of these
executables and no recompilation of the libraries is needed.
.PP
It is not (yet) possible execute compressed files with zlibc. However,
there is another package, called \fR\&\f(CWtcx\fR, which is able to uncompress
executables on the fly.  On the other hand \fR\&\f(CWtcx\fR isn't able to
uncompress data files on the fly.  Fortunately, the both zlibc and tcx
may coexist on the same machine without problems.
.PP
.SH Warning
This manpage has been automatically generated from zlibc's texinfo
documentation.  However, this process is only approximative, and some
items, such as crossreferences, footnotes and indices are lost in this
translation process.  Indeed, this items have no appropriate
representation in the manpage format.  Thus I strongly advise you to use
the original texinfo doc.
.TP
* \ \ 
To generate a printable copy from the texinfo doc, run the following
commands:
 
.nf
.ft 3
.in +0.3i
    ./configure; make dvi; dvips zlibc.dvi
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.TP
* \ \ 
To generate a html copy,  run:
 
.nf
.ft 3
.in +0.3i
    ./configure; make html
.fi
.in -0.3i
.ft R
.lp
 
\&\fRA premade html can be found at:
\&\fR\&\f(CW\(ifhttp://www.tux.org/pub/knaff/zlibc/zlibc.html\(is\fR
.TP
* \ \ 
To generate an info copy (browsable using emacs' info mode), run:
 
.nf
.ft 3
.in +0.3i
    ./configure; make info
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.PP
The texinfo doc looks most pretty when printed or as html.  Indeed, in
the info version certain examples are difficult to read due to the
quoting conventions used in info.
.PP
.iX "c bugs"
.iX "c ALPHA patches"
.iX "c patches"
.iX "c diffs"
.iX "c mailing list"
.PP
.SH Where\ to\ get\ zlibc
.PP
Zlibc can be found at the following places (and their mirrors):
 
.nf
.ft 3
.in +0.3i
ftp://zlibc.linux.lu/zlibc-0.9j.tar.gz
ftp://www.tux.org/pub/knaff/zlibc/zlibc-0.9j.tar.gz
ftp://ibiblio.unc.edu/pub/Linux/libc/zlibc-0.9j.tar.gz
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.PP
Before reporting a bug, make sure that it has not yet been fixed in the
Alpha patches which can be found at:
 
.nf
.ft 3
.in +0.3i
http://zlibc.linux.lu/
http://www.tux.org/pub/knaff/zlibc
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.PP
These patches are named
\&\fR\&\f(CWzlibc-\fR\fIversion\fR\fR\&\f(CW-\fR\fIddmm\fR\fR\&\f(CW.taz\fR, where version
stands for the base version, \fIdd\fR for the day and \fImm\fR for the
month. Due to a lack of space, I usually leave only the most recent
patch.
.PP
There is an zlibc mailing list at zlibc @ www.tux.org .  Please
send all bug reports to this list.  You may subscribe to the list by
sending a message with 'subscribe zlibc @ www.tux.org' in its
body to majordomo @ www.tux.org . (N.B. Please remove the spaces
around the "@" both times. I left them there in order to fool
spambots.)  Announcements of new zlibc versions will also be sent to
the list, in addition to the linux announce newsgroups.  The mailing
list is archived at http://www.tux.org/hypermail/zlibc/latest
.PP
.SH Installing\ zlibc
.iX "v LD_PRELOAD"
.iX "c Installation"
.iX "c Set-uid programs"
.iX "c Boot problems"
.TP
1.\ 
If you install zlibc on Linux, make sure that your shared loader
(ld-linux.so.1/ld.so) understands \fR\&\f(CWLD_PRELOAD\fR. (Best if
ld.so-1.8.5 or more recent)
.TP
2.\ 
Type \fR\&\f(CW./configure\fR. This runs the GNU autoconfigure script which
configures the \fR\&\f(CW\(ifMakefile\(is\fR and the \fR\&\f(CW\(ifconfig.h\(is\fR file.  You may
compile time configuration options to \fR\&\f(CW./configure\fR, see for
details.
.TP
3.\ 
Type \fR\&\f(CWmake\fR to compile zlibc.
.TP
4.\ 
Type \fR\&\f(CWmake install\fR to install zlibc and associated programs to its
final target.
.TP
5.\ 
To use this module, set the environment variable \fR\&\f(CWLD_PRELOAD\fR to
point to the object. Example (sh syntax):
.IP
 
.nf
.ft 3
.in +0.3i
      LD_PRELOAD=/usr/local/lib/uncompress.o
      export LD_PRELOAD
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.IP
or (csh syntax):
.IP
 
.nf
.ft 3
.in +0.3i
      setenv LD_PRELOAD /usr/local/lib/uncompress.o
.fi
.in -0.3i
.ft R
.lp
 
\&\fROn linux, use /lib/uncompress.o instead of /usr/local/lib/uncompress.o .
.IP
You might want to put these lines in your \fR\&\f(CW\(if.profile\(is\fR or
\&\fR\&\f(CW\(if.cshrc\(is\fR in order to have the uncompressing functions available all
the time.
.TP
6.\ 
Compress your files using gzip and enjoy
.PP
For security reasons, the dynamic loader disregards environmental
variables such as \fR\&\f(CWLD_PRELOAD\fR when executing set uid programs.
.PP
However, on Linux, you can use zlibc with set uid programs too, by using
one of the two methods described below:
.TP
1.\ 
You may ing the path to \fR\&\f(CW\(ifuncompress.o\(is\fR into
\&\fR\&\f(CW\(if/etc/ld.so.preload\(is\fR instead of using \fR\&\f(CWLD_PRELOAD\fR.
.IP
\&\fBWARNING\fR: If you use \fR\&\f(CW\(if/etc/ld.so.preload\(is\fR, be sure to
install \fR\&\f(CW\(ifuncompress.o\(is\fR on your root filesystem, for instance in
\&\fR\&\f(CW/lib\fR, as is done by the default configuration.  Using a directory
which is not available at boot time, such as /usr/local/lib will cause
trouble at the next reboot!
.IP
It is also careful to remove zlibc from \fR\&\f(CW\(if/etc/ld.so.preload\(is\fR when
installing a new version.  First test it out using \fR\&\f(CWLD_PRELOAD\fR,
and only if everything is ok, put it back into
\&\fR\&\f(CW\(if/etc/ld.so.preload\(is\fR.  The zlibc package also supplies four
statically linked programs \fR\&\f(CWsrm\fR, \fR\&\f(CWsmv\fR, \fR\&\f(CWsln\fR and
\&\fR\&\f(CWssln\fR, which are equivalen to \fR\&\f(CWrm\fR, \fR\&\f(CWmv\fR, \fR\&\f(CWln\fR and
\&\fR\&\f(CWln -s\fR.  These can be used in case anything goes wrong with the
installation.
.TP
2.\ 
If you have a version of \fR\&\f(CWld.so\fR which is more recent than
\&\fR\&\f(CW1.9.0\fR, you can set \fR\&\f(CWLD_PRELOAD\fR to just contain the basename
of \fR\&\f(CW\(ifuncompress.o\(is\fR without the directory.  In that case, the file is
found as long as it is in the shared library path (which usually
contains \fR\&\f(CW\(if/lib\(is\fR and \fR\&\f(CW\(if/usr/lib\(is\fR)). Because the search is
restricted to the library search path, this also works for set-uid
programs.
.IP
Example (sh syntax):
.IP
 
.nf
.ft 3
.in +0.3i
      LD_PRELOAD=uncompress.o
      export LD_PRELOAD
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.IP
or (csh syntax):
.IP
 
.nf
.ft 3
.in +0.3i
      setenv LD_PRELOAD uncompress.o
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.IP
The advantage of this approach over \fR\&\f(CW\(ifld.so.preload\(is\fR is that zlibc
can more easily be switched off in case something goes wrong.
.PP
.SH Using\ zlibc
.iX "c Symbolic links"
.PP
Once zlibc is installed, simply compress your biggest datafiles
using gzip. Your programs are now able to uncompress these files on the
fly whenever they need them.
.PP
.SS Zlibc\ and\ links
.PP
.SS \ \ Symbolic\ links
.PP
After compressing your datafiles, you also need to change any potential
symbolic links pointing to them.  Let's suppose that \fR\&\f(CW\(ifx\(is\fR is a
symlink to \fR\&\f(CW\(iftstfil\(is\fR:
.PP
 
.nf
.ft 3
.in +0.3i
> echo 'this is a test' >tstfil
> ln -s tstfil x
> ls -l
total 1
-rw-r--r--   1 alknaff  sirac          15 Feb 25 19:40 tstfil
lrwxrwxrwx   1 alknaff  sirac           8 Feb 25 19:40 x -> tstfil
.fi
.in -0.3i
.ft R
.lp
 
\&\fR
.PP
After compressing it, you'll see the following listing: