man zlibc.conf (Formats) - zlibc's configuration file

Name

zlibc.conf - zlibc's configuration file

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.

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To generate a printable copy from the texinfo doc, run the following commands: 
    ./configure; make dvi; dvips zlibc.dvi
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To generate a html copy, run: 
    ./configure; make html
A premade html can be found at: CWhttp://www.tux.org/pub/knaff/zlibc/zlibc.html
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To generate an info copy (browsable using emacs' info mode), run: 
    ./configure; make info

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.

Description

To get its configuration, zlibc first looks into the file described by the environment variable CWLD_ZLIB_CONFFILE (if any), then in CW~/.zlibrc and finally in CW/usr/local/etc/zlibc.conf (CW/etc/zlibc.conf on Linux ). If the desired information is found in neither of these files, the compiled-in defaults are used. It is possible to supply only part of the needed information in the configuration files. In that case, the missing information is retrieved from the compiled-in defaults. This allows you to have really small runtime configuration files, which only list the differences between the desired configuration and the compiled-in configuration.

If an error occurs while parsing one of the configuration files, the offending file is skipped, and the search continues with the next file. However, no error message is printed unless the environmental variable CWLD_ZLIB_VERBOSE is turned on (i.e. set to CW1 or to CWon ).

If two files contain contradictory information, the information in the file which is scanned first is retained (usually CW~/.zlibrc). If any flags have been set or unset using environmental variables, these settings override the flags specified in the configuration files.

The configuration files are read by each process. For each process, they are read at most once, at the time when zlibc is first used (attempt to access a compressed file). Afterwards they are cached in the process's virtual memory. Thus, changing zlibc configuration files doesn't generally have any effect on already running processes.

Overall structure

The zlibrc files consist of two sections: A commands section (Commands line flags) and a class definition section (Class section).

The commands section describes how zlibc should behave depending on the executable that it was called from. Several commands are grouped together into command classe.

The class definition section describes how zlibc should behave depending on the class of the command and the datafile opened.

The configuration file may contain comments in both sections: a comment starts with a hash (CW#) and stops at the end of the line.

Dashes (CW-) and underbars (CW_) may be used indifferently in all keywords.

Commands section

General syntax of the commands section

The format for a line in the "commands" section is as follows:

CWcommands "cmd1CW" [ ... CW"cmdnCW" ] CWuse flags CW"classCW"

In this line, the cmd1 ... cmdn are the basenames of the programs (commands) for which this line should apply. The basename is the name without the path, i.e. CWls instead of CW/usr/bin/ls. The command names should be enclosed in quotes. You may also use the keyword CWdefault (without quotes) to match all commands.

The flags describe those aspects of zlibc's behaviour that are independant from the datafile which is being accessed. These flags come in pairs. The flags need not to be listed on a single CWcommands line, they may occur in several places, even in several different configuration files (for instance one in CW/etc/zlibc.conf and another one in CW~/.zlibrc.

If two contradictory flags are found in the configuration files, the one which is seen first is taken.

If on the other hand a certain flag is not found at all in the configuration files, the compiled-in default for this flag is used. This is usually the second flag of each pair, described below (see section Commands line flags).

These flags can all be overridden by environmental variables. When the corresponding environmental variable is set to CW1 or to CWon, the first flag is used, when it is set to CW0 or to CWoff. If the environmental variables is set to neither of these 4 values, it is ignored).

The class names the commands class that these commands belong to. If, for a given command, two CWcommands lines give different classes, the one which is seen first is taken. No union of classes is made, the classes are always treated as a whole. Thus, if you want to make a change to a command class, you need to describe it in its entirety.

The following example says that the CWtar, CWcpio, CWpax, CWcp and CWmv show compressed files in a directory listing (CWreaddir_compr flag), and are of class CWgeneric_safe. 

commands "tar" "cpio" "pax" "cp" "mv" use readdir_compr "generic_safe"

The class CWgeneric_safe would then need to be described further in the class section.

Available commands line flags

This section describes the flags which can be used on a CWcommands line. All these flags come in pairs.

The table below describes each of these pairs. The first word in the header of each item is the non-default flag, the second word is the default flag, and the third word is the environmental variable by which you can override the settings from the configuration files. If this environmental variable is turned on (set to 1), the non-default (first) flag is taken, if it is turned off (set to 0), the default (second) flag is taken.

CWdisable / enable / LD_ZLIB_DISAB
The CWdisable flag disables zlibc for the programs on this commands line. This is useful for compression and uncompression utilities. Without this flag, CWgunzip would not work anymore, because it would think that the uncompressed file exists already, and it would refuse to overwrite this file.
CWdisable_child / enable_child / LD_ZLIB_DISAB_CHILD
The CWdisable_child flag disables zlibc for the programs started by programs on this commands line. This is implemented by removeing all occurrences of CWuncompress.o from the LD_PRELOAD environment variable. This function is useful for programs such as xemacs, in order to make sure that all launched subprograms return results consistent with emacs itself (directory listings, etc)
CWreaddir_compr / readdir_uncompr / LD_ZLIB_READDIR
The readdir function shows the uncompressed files (i.e. with their trailing CW.gz extension) when the CWreaddir_compr flag is set, and the compressed files otherwise.
CWverbose / silent / LD_ZLIB_VERBOSE
When CWverbose is set, zlibc prints informational messages.
CWunlink / no_unlink / LD_ZLIB_UNLINK
If the CWunlink flag is set, and if the user program tries to unlink a virtual (uncompressed) file, the package translates this call into unlinking the real file. If the CWno_unlink flag is set, requests to unlink virtual (uncompressed) files are silently ignored.

Class section

A command class definition describes those aspects of zlibc's behavior that depend on the name of the datafile which is being accessed. Command classes are identified by a name which is matched against the class parameter from the commands. The class name should be enclosed between quotes both in the commands line and in the class definition.

The class section contains descriptions of different command classes (i.e descriptions how datafiles should be uncompressed). Each class definition begins with a line of the following format:

CWclass "idCW"

The class id is the same string as the one used in the commands line. The remaining lines of a class definition are as follows: [ [ criterion ] [ CW"nameCW" ]] mode

The following example shows the definition of the class used for X-servers. 

# X uses tmp files in its own directories.
class "X"
subdir "/usr/X11R6" usetmpfile
subdir "/usr/X386" usetmpfile
subdir "/usr/lib/X11" usetmpfile
showpipe

This says that all compressed files who are in a subdirectory below CW/usr/X11R6, CW/usr/X386 or CW/usr/lib/X11 are decompressed using temporary files (CWusetmpfile), and that files from other directories are decompressed using pipes (CWshowpipe)

The following examples illustrates a command class, named CWnopipe, which always uses temporary files for decompression # generic class which uses temp files for all files. class "nopipe" usetmpfile

File selection Criteria

The criterion describes what parts of the filename should match:

CWfilename
The entire filename of the target data file must match name.
CWbasename
The basename (filename without directory) of the target data file must match name.
CWdirectory
The data file must live in the directory name. If the user program opens the file with an absolute pathname, that filename is used as is. If on the other hand the user program uses a relative pathname, zlibc uses the most direct path to the file (i.e. without symlinks).
CWsubdirectory
The data file must live in the directory name or in one of its subdirectories. If the user program opens the file with an absolute pathname, that filename is used as is. If on the other hand the user program uses a relative pathname, zlibc uses the most direct path to the file (i.e. without symlinks).
CWsuffix
The data file's name must end in name. This is useful for selecting files according to their extension.
CWfilesystem
The data file must live on the same filesystem as name. This criterion can for example be used for example to disable zlibc on a doublespaced filesystem (where zlibc would be redundant), or to switch off uncompressed size reporting on an CWftpfs filesystems .
CWdefault
All data files match. All class definitions must have a default line, and this default line must be the last line of the definition. The default criterion needs no 'name' parameter.
CWall
All data files match. Unlike CWdefault, this line needs not to be the last line of the class definitions. Thus it is possible to specify several CWall lines for different aspects of CWzlibc behaviour.

The lines of each class definition are scanned in sequence, and, for each aspect, the first matching line is adopted. The class may be defined in another initialisation file, if this file is scanned later. The criterion parameter may be omitted if it can be deduced from the name. In that case, the following heuristics are used:

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Names beginning with a dot are considered as CWsuffix.
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Names beginning with a slash, but not ending with a slash are considered as filename.
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Names beginning and ending with a slash are considered as CWsubdirectory.
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A missing name is considered as CWdefault.
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All the other names are considered as CWbasename.