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man-db - the database cached manual pager suite

Graeme W. Wilford <eep2gw@ee.surrey.ac.uk>
Colin Watson <cjwatson@debian.org>

This document describes the setup, maintenance and use of a generic
manual page system with special reference to the man-db package and
its advanced features.

man-db v2.12.0 2023-09-23

UNIX is a registered trademark of the X/Open Company, Ltd.
NFS is a registered trademark of Sun Microsystems, Inc.
PostScript is a registered trademark of Adobe in the United States.

The general conventions used throughout this manual include

o file names and paths in italic, e.g. /usr/share/man.
o variable strings (usually path components) enclosed within <> and in
italic, eg. <sec>,
o program names in bold, eg. man.
o commands that can be typed at a shell prompt in a box, eg. man foobar.
o environment variables denoted as follows: $ENV_VAR

Permission is granted to make and distribute verbatim copies of this manual
provided the copyright notice and this permission notice are preserved on all
copies.

Permission is granted to copy and distribute modified versions of this manual
under the conditions for verbatim copying, provided that the entire resulting
derived work is distributed under the terms of a notice identical to this one.

Permission is granted to copy and distribute translations of this manual into
another language, under the above conditions for modified versions, except
that this permission notice may be stated in a translation approved by the
copyright holder.

man-db v2.12.0 2023-09-23

1. Introduction

1.1. man-db

man-db is a package that is designed to provide users with information in a
fast and friendly manner while at the same time offering flexibility to the
system administrator.

It is made up of several user programs:
o man - an interface to the system reference manuals
o whatis - search the manual page names
o apropos - search the manual page names and descriptions
o manpath - determine search path for manual pages
o lexgrog - directly read header information in manual pages
several maintenance programs:
o mandb - create or update the manual page index caches
o catman - create or update the pre-formatted manual pages
and a special pre-formatter that knows about compressed manual pages:
o zsoelim - satisfy .so requests in roff input

In addition to these compiled programs, there are two shell scripts, mkcatdirs
and checkman in the tools subdirectory. These scripts aid the creation of cat
directories and check for duplicated manual pages, respectively.

The following manual pages are provided with this package to explain correct
format and usage. man(1), whatis(1), apropos(1), manpath(1), lexgrog(1), man-
path(5), mandb(8), catman(8) and zsoelim(1).

1.1.1. The concept

man-db originally started out life as program suite man-1.1B, written by John
W. Eaton <jwe@che.utexas.edu> and maintained by Rik Faith <faith@cs.unc.edu>
to which support proposed by the newly formed FSSTND committee regarding cat
directories was added.

Since then, man-db's most innovative feature: the database cache scheme[1] has
been significantly developed. The basic idea was to reduce manual page search
times to a minimum. The following piece of text is included from the man-
db-2.2 distribution:

The theory: If you go to a library to take a book out, what do you do?

a) Go and look where it might be on a micro-fiche/terminal, take a
look where it is supposed to be on the shelf, and then go look at the
new arrivals if it's not where it's supposed to be?

OR
____________________
[1] originally conceived after observing the actions of the Perl-based man-
ual pager suite, man-pl written by Tom Christiansen <tchrist@convex.com>

man-db v2.12.0 2023-09-23

b) Start at one end of the ground floor, look along every bookshelf
until you've completed that floor, then go up a level and start again
until you've found what you're looking for?

Since then the database index scheme has evolved greatly. Every manual page
and stray cat page on the system is registered in an index database cache
which stores various details about the file including the timestamp, the loca-
tion and the whatis[2] information. This information is kept up to date by
regular runs of mandb. In some configurations man also looks for filesystem
changes each time it is invoked and helps to keep the database cache current,
but this imposes a penalty on manual page search times.

1.2. The manual page system

The simplest manual page system will have a single manual page hierarchy.
This will typically be

/usr/share/man

beneath which will be several subdirectories of the form man<sec> where <sec>
is 1, 2, 3, 4, 5, 6, 7 or 8. These are referred to as sections of the manual.
Others may exist and they are not restricted to single character names. eg.

/usr/share/man/manfoo

is a valid section subdirectory. Other common sections include 9, n, l, p and
o.

Within these section subdirectories reside the manual pages themselves. Their
filenames follow the pattern

/usr/share/man/man<sec>/<name>.<sec><ext>

where in most cases <ext> is an empty string. An example is manual page cp

/usr/share/man/man1/cp.1

which resides in section 1 and has no special extension.

1.3. Sections of the manual

The manual is split up into sections to ease access and to cater for manual
pages that share the same name. It is common for a program and function to
share the same name. kill is a good example. This is both a program which
can be used to send a process a signal and an operating system call with simi-
lar functionality. Their manual pages are stored under sections 1 and 2 re-
spectively. Thus, sections are used to separate out the program manual pages
from the function manual pages and so on. The table below shows the section
____________________
[2] one line description of the manual page

man-db v2.12.0 2023-09-23

numbers of the manual followed by the types of pages they contain.

+---------+------------------------------------------------------+
| Section | Section contents |
+---------+------------------------------------------------------+
| 1 | user executable programs or shell commands |
| 2 | system calls (functions provided by the kernel) |
| 3 | library calls (functions within system libraries) |
| 4 | special files (usually found in /dev) |
| 5 | file formats and conventions eg. /etc/passwd |
| 6 | games |
| 7 | macro packages and conventions eg. man(7), groff(7). |
| 8 | system administration commands |
| 9 | kernel routines [Non-standard] |
| n | new [obsolete] |
| l | local [obsolete] |
| p | public [obsolete] |
| o | old [obsolete] |
+---------+------------------------------------------------------+

1.4. The format of manual pages

The format in which manual pages are stored is NROFF/TROFF or more generally
ROFF. This is a typesetter style language[3] which requires formatting before
being viewed. In fact some manual pages require pre-format processing to cor-
rectly format tables or equations.

If the page is to be viewed on screen in a text environment, NROFF is used as
the primary formatter. If the page is to be printed or displayed in a graphi-
cal environment, TROFF is used. Traditionally, TROFF formatted files for a
C/A/T (Computer aided Typesetter) which is now obsolete.

The GNU ROFF (GROFF[4]) suite of programs offer a choice of output types in-
cluding X, dvi and postscript. When configuring man-db, the preference is to
use GROFF rather than TROFF.

1.5. Arguments to configure

To allow the configuration program, configure, to be non-interactive, it can
be passed various options to alter the default settings. Generic configure
options are discussed in docs/INSTALL. Options that are specific to the
man-db package are described below.

____________________
[3] similar in some aspects to TeX
[4] Written by James Clark <jjc@jclark.com> and now maintained by Ted Hard-
ing <ted.harding@nessie.mcc.ac.uk> and Werner Lemberg <wl@gnu.org>

man-db v2.12.0 2023-09-23

--enable-cache-owner[=ARG]
By default, system-wide cache files will be owned by user man. Use this
option with an argument to change the cache file owner.

--disable-cache-owner
Use this option to leave the ownership of system-wide cache files uncon-
strained. Users will be allowed to modify them.

--disable-setuid
By default, man will be installed as a setuid program to the user that
owns the system-wide cache files. Use this option to install man as a
non-setuid program instead.

--enable-mandirs=OS
By default, man-db supports manual page directories in any of several
layouts used by free and proprietary versions of UNIX. However, in cer-
tain cases, this can cause man-db to find the wrong page by mistake, es-
pecially when the names of some manual pages on the system contain peri-
ods. Use this option with an argument of GNU, HPUX, IRIX, Solaris, or
BSD (or more than one of these, separated by commas) to support only the
layouts typically used on each of those systems. Note that man-db is not
currently capable of writing cat pages in the proper BSD layout.

--with-device=DEVICE
Use this flag to alter the default output device used by NROFF. DEVICE is
passed to NROFF with the -T option. configure will test that NROFF will
run with the supplied device argument.

--with-db=LIBRARY
configure will look for database interface libraries in the order gdbm,
Berkeley DB and finally ndbm and will #define appropriate variables rela-
tive to the first one found. To override the built-in order on platforms
having a choice of interface library, use this option to specify which
library to use.

--enable-automatic-create
If this flag is used, man will automatically create index databases for
users' private manual page hierarchies.

--disable-automatic-update
Normally, man will update entries in index databases if it finds newly
installed manual pages (if the --update flag is used) or delete entries
if manual pages are removed. This flag suppresses this behaviour.

--disable-cats
Normally, man will automatically try to create cat files corresponding to
manual files when a manual page is read. This flag suppresses this be-
haviour.

--disable-manual
Don't build or install the man-db manual. This may be useful when cross-
compiling, or to reduce the installation size.

man-db v2.12.0 2023-09-23

2. The specifics of Sections

2.1. Package specific manual page sections

The use of package specific manual page sections is discouraged as packages
large enough to warrant their own section probably contain manual pages that
span other sections. An example might be package foo that has its own section

/usr/share/man/manfoo

which contains manual pages describing its programs, the library routines it
offers and the format of several of its configuration files. These pages
would normally be allocated to sections 1, 3 and 5 respectively and thus com-
bining them all under section foo is misleading. Subtle problems will arise
if there are any base name-space clashes with standard manual pages, e.g.
exit(3), exit(foo) and the order in which they should be shown.

There are two standard solutions to this problem.

(1) Create a separate manual page hierarchy for the package's manual pages
such as

/usr/local/packages/foo/man

(2) Install the pages in their relevant sections, with a unique extension
appended to the filename such that

/usr/share/man/manfoo/exit.foo

would instead be installed as

/usr/share/man/man1/exit.1foo

Only (2) offers a complete solution to manual page ordering problems and al-
lows users to access the desired page directly.

2.2. Selecting a section type

2.2.1. Specifying a section

This is done via use of the section argument to man

man 1 exit

will look for exit.1* in section 1 of the manual. If exit.1 exists, it will
be displayed in preference to exit.1foo

man 1foo exit

will look for exit.1foo* in section 1 of the manual. The asterisk (*) repre-
sents a wild-card of any type or length, including length zero.

man-db v2.12.0 2023-09-23

For an argument to be interpreted as a section name rather than a page name,
it must either begin with a digit, or be included in the standard section
list. The default section list is defined in include/manconfig.h to be 1, n,
l, 8, 3, 2, 5, 4, 9, 6 and 7. This should be modified in order and content to
meet the local conventions. It may be altered at run-time using the SECTION
directive in the man-db configuration file.

Every subdirectory section name in the entire system must be in the list, in-
cluding sections found in imported manual page hierarchies. It is not neces-
sary to list sections with extensions unless a special ordering for those ex-
tensions is desired. The order is important because in normal operation, man
will only display the first manual page it finds that meets the search crite-
ria. Using the --all argument will cause man to attempt to display all manual
pages that meet the criteria. See man(1) for further information.

Having an excess of sections listed will not slow man down.

2.2.2. Specifying an extension

If the section is unknown, but the package extension is, it is possible to use
the extension argument

man -e foo exit

to search in all sections for manual pages named exit from package foo.

man-db v2.12.0 2023-09-23

3. Filesystem structure

3.1. Manual page hierarchies

It is often common for manual page systems to have more than one manual page
hierarchy. Indeed one of the systems I use has the following globally acces-
sible hierarchies

/usr/man
/usr/local/man
/usr/local/tex/man
/usr/local/pbm/man
/usr/X11R6/man
/usr/openwin/man
/usr/local/packages/pvm/man

A full system $MANPATH would be a colon separated list of these directories.
The order is important, and is observed by man-db's search algorithms. The
order is very much related to the user's $PATH environment variable, and
should be set on a per user basis, or not set at all. If a user's $PATH
causes

/usr/local/packages/bin/foobar

to be executed in preference to

/usr/bin/foobar,

it is essential that

man foobar

displays the manual page located within

/usr/local/packages/man

rather than within

/usr/share/man

To ensure correct order, the program manpath may be used to set the $MANPATH
environment variable. See manpath(1) and manpath(5) for details.

3.2. Setting the MANPATH

If using a Bourne style login shell such as bash, ksh, or zsh, the commands

export MANPATH
MANPATH=`manpath -q`

can be added to $HOME/.profile

man-db v2.12.0 2023-09-23

If using a C style login shell such as csh or tcsh, the commands

setenv MANPATH `manpath -q`

can be added to $HOME/.login

N.B. $PATH must be set prior to using manpath. The setting of $MANPATH is
actually unnecessary as the man-db utilities will dynamically determine the
manpath if $MANPATH is unset.

3.3. Determination of the internal manpath

All man-db utilities, manpath included, will use the user's $MANPATH environ-
ment variable if set and not equal to "". Otherwise the user's $PATH environ-
ment variable is queried. If this is unset or is set to "", the determined
manpath will simply be any

MANDATORY_MANPATH

elements defined in the man-db config file.

Assuming that a $PATH exists, each path element it contains is scanned for in
the config file. If found, the corresponding manpath element is appended to
the internal manpath. However, if the element is not mentioned in the config
file, a man directory relative to it will be sought. The subdirectories
../man, man, ../share/man, or share/man relative to the path component are ap-
pended to the internal manpath if they exist. Finally, the internal manpath
is stripped of duplicate paths before being processed by the NLS and `Other
OS' routines. These may add to or modify the separate path elements giving
priority to NLS manual pages or add OS-relative manpaths.

3.4. Other OS's manual pages

It is common to have collections of heterogeneous computer systems linked to-
gether in a network. In some circumstances[5] it is advantageous to be able
to access the manual pages of these other systems directly from your system.
This feature is known as alternate system support. The accepted way to setup
this support is to NFS mount the respective systems' manual page hierarchies
under the native manual page hierarchies. An example:

____________________
[5] writing portable software instantly comes to mind

man-db v2.12.0 2023-09-23

Rather than have multiple NFS mounts from a single machine, this may be accom-
plished by NFS mounting

<other-sys>:/usr

somewhere on the local system and using symbolic links within the manual hier-
archies. To access these alternate systems using man use the -m or --systems
option, eg.

man --all --systems userix:newOS 5 passwd

would provide manual pages showing the structure of /etc/passwd on systems
userix and newOS in that order. A manual page would not be displayed about
the local systems conventions. Please read the relevant man-db utility's man-
ual page for further and more specific information.

3.5. NLS manual pages

NLS manual pages should be installed in NLS subdirectories of a standard man-
ual page hierarchy. The subdirectory names should be made up of language,
territory, and character set components as necessary to specify the locale of
the manual page.

The character set component describes the encoding of the manual page itself,
and not the encoding in use by the user; a manual page installed under the
fr.UTF-8 subdirectory will be used in the fr_FR.ISO-8859-1 locale as well as
fr_FR.UTF-8, and converted between encodings as necessary. If no character
set is specified in the subdirectory name, man-db will attempt to detect
whether each page is encoded using UTF-8 or a legacy character set appropriate
for the language. Accordingly, the recommended scheme for installing manual
pages is to encode them in UTF-8 (or, if that is not practical, in the legacy
character set) and install them in directories without a character set compo-
nent in their names.

The territory should normally be omitted unless it is necessary to describe
the manual page text. For example, Brazilian Portuguese is quite distinct
from Portuguese and so should be installed under the pt_BR subdirectory, but a
single German manual page will typically suffice in Austria as well as in Ger-
many and so should be installed under the de subdirectory.

man-db v2.12.0 2023-09-23

The following table gives some examples.

On systems supporting UTF-8, it is recommended that all manual pages be en-
coded using UTF-8 where possible, in order to simplify the task of editing a
variety of pages without reconfiguring editors and terminals and the like.

Each of these directories are then interpreted as manual page hierarchies
themselves and may contain the usual section subdirectories. Access to NLS
manual pages is achieved via use of the setlocale(3) function which queries
user environment variables to determine the current locale. Internally to the
man-db utilities, this locale string is appended to each manpath element and
the resultant NLS manpath element is searched before the standard manpath ele-
ment. In this way, an NLS manual page that matches the search criteria will
be shown before or in place of the standard American English page.

If a user's $MANPATH consists of or is determined as

/usr/local/man:/usr/share/man:/usr/X11R6/man

and their locale is set to de_DE, the command

man --systems userix:man foobar

would produce the following internal man-db manpath elements

/usr/local/man/userix/de_DE
/usr/local/man/userix/de
/usr/local/man/userix
/usr/share/man/userix/de_DE
/usr/share/man/userix/de
/usr/share/man/userix
/usr/X11R6/man/userix/de_DE
/usr/X11R6/man/userix/de
/usr/X11R6/man/userix
/usr/local/man/de_DE

man-db v2.12.0 2023-09-23

/usr/local/man/de
/usr/local/man
/usr/share/man/de_DE
/usr/share/man/de
/usr/share/man
/usr/X11R6/man/de_DE
/usr/X11R6/man/de
/usr/X11R6/man

foobar would be searched for in the order of manual page hierarchies listed.
Additional directories corresponding to manual pages encoded in different
character sets would be used if present.

3.5.1. ISO 8859-1 (latin1) manual pages

By default NROFF will format manual pages into a form suitable for a type-
writer style device, e.g. a terminal screen. GNU NROFF is capable[6] of for-
matting ROFF into a form suitable for 8-bit latin1 capable output devices. To
enable output for such a device, give the option

--with-device=DEVICE

to configure where DEVICE is the suitable and supported output format, in this
case latin1.

3.5.2. Displaying non-ASCII characters on a Linux virtual terminal

To view non-ASCII characters at the Linux console, you must have one of the
kbd[7] and console-tools packages installed. If your system does not come
with suitable configuration already, then please see the documentation in the
kbd or console-tools package for details on how to configure the console for
your locale. On modern systems, the best choice is likely to be to use the
UTF-8 encoding with a font suitable for your language. Make sure that your
locale environment variables match the encoding displayed by the console. For
display under the "X Window System", a suitable 8-bit-clean terminal emulator
is required.

3.5.3. Viewing ASCII pages formatted for latin1 output device

When formatting an ASCII manual page for a latin1 output device, GNU NROFF
will take advantage of the extra characters available and will always produce
a text page containing some latin1 (8-bit) symbols. The table[8] below, taken
from man(1), illustrates the differences.

____________________
[6] see nroff(5) for the output device formats available with your NROFF
[7] written and maintained by Andries Brouwer <aeb@cwi.nl>.
[8] The ISO 8859-1 and ASCII columns of this table will be identical if
this manual was formatted for an ASCII based typewriter display, i.e. using
NROFF in its native mode.

man-db v2.12.0 2023-09-23

+---------------------+-------+------------+-------+
| Description | Octal | ISO 8859-1 | ASCII |
+---------------------+-------+------------+-------+
| continuation hyphen | 255 | | - |
| bullet (middle dot) | 267 | o | o |
| acute accent | 264 | ' | ' |
| multiplication sign | 327 | x | x |
+---------------------+-------+------------+-------+

To display such symbols on a 7 bit terminal or terminal emulator, they must be
translated back into standard ASCII. The -7 option with man will enable this
simple reverse translation.

This option may be useful if your site has both 7 and 8-bit capable output de-
vices and nroff is using the latin1 output device to format manual pages.

3.6. Cat pages

It has become standard practice to store the formatted manual pages on disk so
that subsequent requests for the manual page do not have to involve the for-
matting process. These pre-formatted manual pages are known as cat pages.
Although cat pages require additional disk storage requirements, they provide
a substantial speed increase and their use is recommended.

The automatic support for storing and using cat pages is brought about by sim-
ply creating suitable directories for them.

3.7. Cat page hierarchies

Traditionally, cat pages were stored under the same manual hierarchy as their
source manual pages, in cat<sec> subdirectories rather than man<sec>. This
situation is rather limiting in several situations:

o When it is advantageous to mount /usr as a read-only filesystem. Cat pages
cannot be supported in this situation without use of symbolic links to var-
ious other areas of the filesystem. This situation is a greater problem if
the media itself is read-only, such as CD-ROM.
o When NFS mounting alternate OS's manual page hierarchies. The alternate
system may be under someone else's control and they may not want cat pages
stored on their system. In fact, it is usually a good idea to export the
manual page filesystems read-only, or import them that way. It is possible
to avoid the problems, this time with even more symbolic links that may
need periodic updating.
o If there is a mixture of normal cat files and stray cats[9], it is very
difficult to periodically trim the cat space disk usage by removing seldom
____________________
[9] cat files that have no source manual page, i.e. they cannot be recreat-
ed.

man-db v2.12.0 2023-09-23

accessed cat files.

To avoid all of these problems simultaneously, it was decided to support local
cat page directory caches.

3.8. Local cat page directory caches

Any location for cat page hierarchy may be specified in the man-db configura-
tion file. The location of the database cache associated with each manual
page hierarchy will always be at the root of the cat page hierarchy. By de-
fault, the cat page hierarchy shadows the manual page hierarchy. The FHS pro-
poses /var/cache/man as the location for such directories, although man-db al-
lows any directory hierarchy to be used. The FHS path transformation rule is
as follows:

/usr/<hierarchy>/share/man/<locale>/man<sec>/page.<sec><ext>

should be formatted into the cat file

/var/cache/man/<hierarchy>/<locale>/cat<sec>/page.<sec><ext>

where the <locale> directory component may be missing and <ext> may be an
empty string.

The suggestion is that stray cats are located in the traditional hierarchy un-
der /usr whereas re-creatable cat pages are stored under the local writable
hierarchy /var/cache/man. man follows strict rules in determining which file
is displayed.

As an example, the following route is taken if all three files exist.

(1) Check relative modification time stamps of the manual file and the tra-
ditional cat file. If the cat file is up to date (has an equal time
stamp), display it.

(2) The traditional cat file is out of date. Check relative time stamps of
the manual file and the alternate cat file. If the cat file is up to
date, display it.

(3) The alternate cat file is out of date. Format the manual file and dis-
play the result in the foreground, while updating the alternate cat
file in the background.

When a cat file is created, its time stamp is set to that of the corresponding
manual file. Manual files are often stored in tar archives, and time stamps
may be preserved when these archives are unpacked. Simply checking whether
the cat file is newer would sometimes cause man to display an out-of-date cat
file in this case, when it should have reformatted the manual file instead.

man-db v2.12.0 2023-09-23

4. Compression

4.1. Compressed manual pages

It is possible to maintain a system of compressed manual pages. This imposes
a small overhead on the formatting process, but is nevertheless usually rea-
sonable in order to avoid unnecessary consumption of disk space.

Presently, the compression extension/decompressor pairs must be known at com-
pile time although any number may be defined and used. The following struc-
ture is predefined in man-db:

+-----------+--------------+
| Extension | Decompressor |
+-----------+--------------+
| gz | gzip -dc |
| z | gzip -dc |
| Z | compress -dc |
+-----------+--------------+

It is a relatively easy operation to include further pairs in this structure.
See lib/compression.c for details and an example.

Support for compressed manual pages is compiled into the man-db utilities by
default, depending on the decompressors available at configure time.

4.2. Compressed cat pages

man-db compresses cat files by default. During configuration, configure will
try to find gzip and, if found, all cat files produced by man will be com-
pressed with

gzip -7c

and have a .gz extension appended. If gzip is not found,

compress -c

is used as the compressor and the extension .Z is appended.

To store cat files in an uncompressed state and to disable compressed exten-
sion processing completely, edit config.h and comment out the following line

#define COMP_CAT 1

4.2.1. Stray cats

Normally, man will only look for cat files with the default compression exten-
sion. The default compression extension is dependent on the default compres-
sor and may be an empty string if the support for compressed cats is disabled.

man-db v2.12.0 2023-09-23

It is possible for a system to be supplied with stray cat files located in the
traditional cat page hierarchy. To make matters worse, they may have compres-
sion extensions other than the default and reside on read-only media. In such
circumstances, stray cat files will be accepted with any compression extension
that is also supported for manual pages.

This special treatment of stray cat pages is removed if support for compressed
manual pages is turned off or not available.

man-db v2.12.0 2023-09-23

5. Formatting

As already pointed out in the introduction, there are two primary formatters
common to UNIX: NROFF and TROFF.

In the following sections, I will use the term TROFF to describe the typeset-
ter formatter and NROFF to describe the typewriter formatter. The term ROFF
will be used to describe a generic formatter.

5.1. GROFF

If using the GROFF package, there is a further choice, GROFF itself. Essen-
tially, GROFF forms a pipeline of processors including TROFF and an output
processor which translates the ditroff produced by TROFF into the appropriate
output format. The default output format, or device, for GROFF is PostScript.
Anything else must be specified using the device argument. To illustrate
GROFF, the command

groff -Tdvi /dev/null

will form the following pipeline

troff -Tdvi /dev/null | grodvi

If GROFF is tied to man's -T option, it is still possible for man to produce
ditroff via use of the -Z option.

In GROFF 1.09, NROFF is bundled as a shell script that calls GROFF, which in
turn calls TROFF with the default options -Wall -mtty-char -Tascii, passing
the result through grotty before it finally reaches the screen.

It is imperative that the script does not pass pre-processing options to
GROFF's command line as man takes care of this separately.

5.2. Devices

Both NROFF and GROFF may allow output device selection. As mentioned previ-
ously, classic NROFF produces output suitable for a typewriter device, classic
TROFF produces output suitable for a C/A/T and GROFF produces output suitable
for a PostScript interpreting device by default.

5.3. Macros

There are several ROFF macro sets in existence that are suitable for manual
pages. Unfortunately, they tend to be incompatible with each other.

During configuration, configure will attempt to determine a suitable macro set
for the local system's manual page collection. It attempts to use NROFF with
the following three macro packages:

man-db v2.12.0 2023-09-23

The first that succeeds is used. The andoc macro set is suitable for manual
pages written using either an or doc macro commands, but not a combination of
both.

5.4. Pre-format processors (pre-processors)

Manual pages may require pre-processing by any of the following

+---------+----+------------------+
| Program | ID | Pre-processes |
+---------+----+------------------+
| eqn | e | equations |
| tbl | t | tables |
| grap | g | graphs |
| pic | p | pictures |
| refer | r | A bibliography |
| vgrind | v | program listings |
+---------+----+------------------+

It is possible to assign a default pre-processor list that all manual pages
will be passed through prior to the primary formatter. By default, this is
empty. To define a default list, edit include/manconfig.h and un-comment the
following line

/* #define DEFAULT_MANROFFSEQ "t" */

which will enable tbl processing by default. To change the list, replace the
t with a suitable string of processor ID's.

Pre-process options may be provided at run time in various forms, but in gen-
eral the pre-processors required by each manual page is indicated in the first
line of the manual page itself. See man(1) for details.

If a manual page does not contain a pre-processor string in its first line, it
will be scanned for well-known ROFF requests used to pass input to certain
pre-processors. Thus, the pre-processor string is often unnecessary for cor-
rect output, but should nevertheless be included for efficiency.

man-db v2.12.0 2023-09-23

5.5. Format scripts

It is very likely that alternate systems manual pages may require non-standard
macro packages or possibly even special pre-processors. To tackle such prob-
lems, special format scripts may be created on a per manual hierarchy basis.

If the file

<manual_hierarchy>/mandb_nfmt

exists and is executable, it is expected to be able to correctly format a man-
ual page originating from <manual_hierarchy> to its standard output. It will
be supplied with either two or three arguments:

o manual page filename
o pre-processor string
o output device (optional)

Similarly, if the option -T<device> or -t was supplied to man and the file

<manual_hierarchy>/mandb_tfmt

exists and is executable, it will be used in the same way.

An example of such a script, supplied by Markus Armbruster <arm-
bru@pond.sub.org>, who provided support for external formatter scripts, can be
found as tools/mandb_fmt-script

The script can be used as both an NROFF and TROFF/GROFF format script and can
be installed as mandb_nfmt and hard linked to mandb_tfmt after modification
appropriate for your particular site.

man-db v2.12.0 2023-09-23

6. The index database caches

As mentioned in the introduction, man-db uses database lookups to search for
manual page locations and information. When performing a manual page lookup
or a basic whatis search, the databases are searched in

key -> content

mode and are as fast as the underlying databases can be. When performing
apropos or special whatis searches, the databases are searched in a linear
way, which, although far more expensive than keyed lookup, is no worse than
traditional text based file searching.

6.1. index database location

The databases are always located at the root of the cat page hierarchy,
whether this is the same as the manual page hierarchy or not. As file locking
mechanisms are employed to ensure that concurrent processes do not update a
database simultaneously, it is almost imperative that the databases reside on
a local filesystem since file locking across NFS filesystems may be unavail-
able or flaky. To avoid such problems, man can be compiled without database
maintenance support. See the section titled "Modes of operation" for details.

6.1.1. Manual hierarchies with no index database

It is possible for the man-db utilities to operate without aid from an index
database. Under such circumstances, search methods will use only file glob-
bing and whatis type searches are performed on any traditional whatis text
databases that may exist. Only the traditional cat hierarchy is searched for
cat files.

6.1.2. User manual page hierarchies

A user may have any number of personal manual page hierarchies listed in their
$MANPATH. By default, man will maintain mandb created databases at the root
of user manual page hierarchies. The definition of a user manual hierarchy is
that it does not have an entry in the man-db configuration file. See man-
path(5) for details.

6.2. Contents of an index database

There are four kinds of entry in an index database.

(1) A direct entry regarding a particular manual page. Manual pages that
are unique in terms of name use just a single entry in the database and
can be looked up by simply using the name as the key.

(2) A common name index entry that lists the extensions of all of the man-
ual pages sharing the common index entry name. Manual pages that share
common names but have differing extensions each have a single database
entry, but this time they are looked up with a key comprised of their
name and their extension. The entire set of common named pages also
has an common name index entry that informs of the extensions

man-db v2.12.0 2023-09-23

available.

(3) An indirect entry that has a pointer to the real entry. Manual pages
that are whatis references to a particular page do not physically exist
so they have a pointer to the entry containing the location of the real
manual page.

(4) Special identification entries. There is one special key name, "$ver-
sion$" that identifies the database storage scheme version.

In order to support looking up manual pages in a case-insensitive fashion,
keys are stored in lower case. If the name of the page was not already in
lower case, its true case is also stored in the common name index entry.

In the following entries, the character "|" will be used to separate the
fields. In reality a tab is used. Direct and indirect entries takes the form:

Common name index entries take the form:

and common name direct or indirect entries take the form:

where in each case the filename being represented is formed as

<manual_hierarchy>/man<sec>/<name>.<ext>.<comp>

in the case of a manual page, or

<cat_hierarchy>/cat<sec>/<name>.<ext>.<comp>

in the case of a stray cat.

If any of the fields would be empty, a single "-" is stored in its place.
<comp> represents the compression extension, <mtime.sec> is an integer repre-
senting the seconds part of the last modification time of the manual page,
<mtime.nsec> is an integer representing the nanoseconds part of the last modi-
fication time of the manual page, <ref> points to the entry containing the lo-
cation of the real page, <ID> is one of the following identification letters,
and <filter> represents any preprocessors that are needed to display the page.

man-db v2.12.0 2023-09-23

+----+------------+--------------------------------------------------------+
| ID | #define | Description |
+----+------------+--------------------------------------------------------+
| A | ULT_MAN | ultimate manual page, the full source nroff file |
| B | SO_MAN | manual page containing a .so request to an ULT_MAN |
| C | WHATIS_MAN | virtual whatis referenced page pointing to an ULT_MAN |
| D | STRAY_CAT | cat page with no source manual page |
| E | WHATIS_CAT | virtual whatis referenced page pointing to a STRAY_CAT |
+----+------------+--------------------------------------------------------+

The ID illustrates the precedence. Some types of manual page can be refer-
enced by several means, e.g. .so requested and whatis referred. In such a
case, only one reference must be stored in the database, the precedence level
decides which.

6.2.1. Favouring stray cats

With the above rules of precedence, it is possible for a valid stray cat page
to be replaced by a whatis referred page sharing identical name-space.

If you would like to see the stray cat page kill(1) instead of the
bash_builtins(1) page referenced by kill(1), edit include/manconfig.h and un-
comment the following line

/* #define FAVOUR_STRAYCATS */

6.2.2. Accessdb

A simple program, accessdb is included with man-db. It will output the data
contained within a man-db database in a human readable form. By default, it
will dump the data from /var/cache/man/index.<db-type>, where <db-type> is de-
pendent on the database library in use.

Supplying an argument to accessdb will override this default. Tabs are re-
placed in the output by a tilde "~" in the key field and a single space in the
content field.

6.2.3. Example database

As an example of both accessdb and the database storage method, the output of

src/accessdb man/index.bt

after first running

src/mandb man

from the top level build directory is included below.

$version$ -> "2.5.0"
accessdb -> "- 8 8 1410381979 324541691 A - - - dumps the content of a man-db database in a human readable format"

man-db v2.12.0 2023-09-23

apropos -> "- 1 1 1410381979 268541692 A - - - search the manual page names and descriptions"
catman -> "- 8 8 1410381979 328541691 A - - - create or update the pre-formatted manual pages"
lexgrog -> "- 1 1 1410381979 268541692 A - - - parse header information in man pages"
man -> "- 1 1 1410381979 280541692 A - t - an interface to the system reference manuals"
manconv -> "- 1 1 1410381979 272541692 A - - - convert manual page from one encoding to another"
mandb -> "- 8 8 1410381979 324541691 A - t - create or update the manual page index caches"
manpath -> " manpath 5 manpath 1"
manpath~1 -> "- 1 1 1410381979 300541691 A - - - determine search path for manual pages"
manpath~5 -> "- 5 5 1410381979 304541691 A - - - format of the /etc/manpath.config file"
whatis -> "- 1 1 1410381979 300541691 A - - - display one-line manual page descriptions"
zsoelim -> "- 1 1 1410381979 304541691 A - - - satisfy .so requests in roff input"

6.3. Database types

man-db has support for various low level database libraries commonly in use
today. The interfaces to the libraries are known as

o ndbm (UNIX)
o gdbm (GNU)
o btree (Berkeley DB)

man-db currently does not hold more than one database open at any time, so

o dbm (UNIX)

support could be added in the future.

6.4. Limitations

The general differences and limitations are best compared in a table.

Those types that have no built in concurrent access strategy are provided with
flock(2) based file locking by man-db.

Berkeley DB initializes its databases very quickly, so btree may have some
performance advantages when doing man searches. However, it is quite
____________________
[10] ndbm databases are physically represented by two files, index.dir and
index.pag, but are referred to simply as index by the interface routines.

man-db v2.12.0 2023-09-23

heavyweight and its library SONAME and on-disk formats have changed a number
of times to provide features considerably beyond what man-db needs, so the
preferred library interface is now gdbm. configure will look for gdbm, btree
and then finally ndbm routines when configuring man-db.

6.5. Sharing databases in a heterogeneous environment
It may be necessary or advantageous to share databases across platforms, re-
gardless of the potential file locking problems.

An example would be a user having a personal manual page hierarchy in an NFS
based home directory environment, whereby the home directory is held on and
mounted from a single machine in a heterogeneous network.

In this context, the database cache will have the same name and reside in the
same place on all machines. There are at least two ways to deal with this
problem.

o Hack the include/manconfig.h file on each platform to provide a unique
database name for each system. No databases will be shared.
o Install and use the Berkeley DB database interface library on each plat-
form. These databases can be shared across big-endian/little-endian plat-
forms although a database created on a big-endian platform will suffer a
small access penalty when used by a litle-endian machine and vice-versa.

man-db v2.12.0 2023-09-23

7. Miscellaneous

7.1. Modes of operation

The man-db utilities can operate in many different modes, allowing varying de-
grees of freedom, functionality and security. No mode requires that the man-
ual page hierarchies be writable.

(1) Default mode
man is setuid to the user MAN_OWNER which is `man' by default and is
changeable via options to configure. mandb, if run by the superuser or
MAN_OWNER, creates globally accessible index databases owned by
MAN_OWNER. Once the databases are created, man will update entries in
them if it finds newly installed manual pages (if the --update flag is
used) or delete entries if manual pages are removed. In this mode it is
possible for a malicious man user to deliberately lock a database as a
writer, thus denying read access to other users.
If cat directories exist and have the correct permissions, man will take
care of producing cat files. These will be owned by MAN_OWNER. The de-
fault permissions of both cat files and databases are 0644.

(2) No man database updates
This mode also requires man to be setuid, but is favoured where databases
must be shared in an environment unfriendly to kernel locking procedures,
eg. NFS. It also prevents possible "denial of service" attacks by mali-
cious man users as man never opens the databases as a writer in this
mode. To replace the functionality lost by disallowing man write access
to the databases, mandb should be rerun whenever new manual pages are in-
stalled. Otherwise, man will not be able to use the database to find and
display the newly added manual pages, and will have to use the filesystem
instead. Each index database may be owned by an arbitrary user who will
have subsequent write access to the database. Cat files are created in
the same way as for mode (1) above.
To use the man-db utilities in this mode, give the option `--disable-au-
tomatic-update' to configure.

(3) No man database updates or cat production
man is installed not setuid. This mode of operation probably offers the
highest level of security but it requires higher levels of maintenance
than other modes due to the restrictions imposed upon man. Each database
is owned by an arbitrary user as in mode (2). Each cat hierarchy is also
owned by an arbitrary user who is responsible for creating cat files us-
ing catman whenever new manual files are installed. man will be com-
pletely passive in its action, i.e. no index databases will be written to
and no cat files are ever produced.
To use the man-db utilities in this mode, supply the options `--dis-
able-cache-owner --disable-setuid --disable-automatic-update --dis-
able-cats' to configure, or build man-db as in mode (1) and install the
binaries without the setuid bit set.

(4) Wide open
man is installed not setuid. This mode is similar in operation to the
majority of vendor supplied, non setuid, cat file supporting manual pager

man-db v2.12.0 2023-09-23

suites. It is not recommended. The databases are owned by an arbitrary
user who maintains them using mandb. man does not update the databases.
Cat files are produced and stored in world writable cat directories and
have world write access themselves.
To use the man-db utilities in this mode, supply the options `--dis-
able-cache-owner --disable-setuid --disable-automatic-update' to config-
ure, edit include/manconfig.h and change the definition of CATMODE from
0644 to 0666.

Other variations can also be used. In fact it is possible for man to actually
create index databases, usually the job of mandb, for users' private manual
page hierarchies. This is enabled by giving the option `--enable-auto-
matic-create' to configure.

In summary, include/manconfig.h contains definitions for

o CATMODE
o DBMODE

the setuid installation and operation of man is modified by supplying either
of the following options to configure:

o --enable-setuid
o --disable-setuid

and other aspects of man's behaviour are controlled by the following options
to configure:

o --enable-automatic-create
o --disable-automatic-update
o --disable-cats

7.2. NFS root squash

If man is installed setuid to an arbitrary user and is run by root, instead of
gaining the effective user id of the setuid user, man is run with both uid and
euid as root. This is neccesary due to infelicities with the POSIX setuid()
function call: All users except root may change to and from the effective
(setuid) user, however once root has setuid(user), there is no way back.

A side effect of this is that NFS mounted cat hierarchies or databases will be
unwritable if the following conditions exist:

o man/catman/mandb is run by root
o The NFS mount has the root squash flag set

To get around this problem, the root user must first attain the ID of the cat
hierarchy or database owner before running man/catman/mandb whenever the data-
bases need updating or cat files are to be produced.

man-db v2.12.0 2023-09-23

7.3. NLS message catalogues

man-db has built in support for native language message catalogues. That is,
it can issue messages in the locale of the user's choice. This will only oc-
cur if the locale's translation has been written. Before undertaking a trans-
lation, please contact the Translation Project (https://translationpro-
ject.org/) who are coordinating such activities.

7.4. Credits

The authors would like to thank the following people for their time, effort,
support, ideas and code which went into man-db:

Markus Armbruster <armbru@pond.sub.org>
Lionel Cons & colleages <cons@dxcern.cern.ch>
Carl Edman <cedman@princeton.edu>
Caleb Epstein <epstein_caleb@jpmorgan.com>
Lars Fenneberg <lf@gimli.comlink.de>
Zoltan Hidvegi <hzoli@cs.elte.hu>
Nils Magnus <magnus@unix-ag.uni-kl.de>
Daniel Quinlan <quinlan@yggdrasil.com>
Fabrizio Polacco <fpolacco@debian.org>
Gordon Sadler <gbsadler1@lcisp.com>
Colin Phipps <cph@cph.demon.co.uk>
Paul Slootman <paul@wurtel.net>
Jose Rodriguez <boriel@airtel.net>
Eirik Fuller <eirik@hackrat.com>
Matej Vela <vela@debian.org>
Clint Adams <schizo@debian.org>
Jeremy C. Reed <reed@reedmedia.net>
Erik Andersen <andersen@codepoet.org>
Giuseppe Sacco <eppesuig@debian.org>
David Weinehall <tao@debian.org>
Ralph Corderoy <ralph@inputplus.co.uk>
Yuri Kozlov <kozlov.y@gmail.com>
Henning Makholm <henning@makholm.net>
Lars Wirzenius <liw@iki.fi>
Nicolas Francois <nicolas.francois@centraliens.net>
Ivan Shmakov <oneingray@gmail.com>
Peter Breitenlohner <peb@mppmu.mpg.de>
Robert Luberda <robert@debian.org>
Chusslove Illich <caslav.ilic@gmx.net>

and all those translators listed in the man/THANKS file.

Glossary

manual page
A file containing descriptions related to the use of a function or pro-
gram or the structure of a file. The name of the file is formed from the
title of the manual page followed by a period followed by the name of the
section that it resides in, optionally followed by an extension. The
format of the file is NROFF and may be compressed, having a suitable com-
pression extension appended.

cat page
A formatted manual page suitable for viewing on a vt100-type terminal.

stray cat page
A cat page that does not have a relative manual page on the system, i.e.
only the cat page was supplied or the manual page was removed after the
cat page had been created.

section
Each manual page or cat page hierarchy is divided into sections, each
section having its own directory. Manual page hierarchy section names
begin with `man' and cat page sections with `cat'.

extension
A package may provide manual pages with filenames ending in a package-
specific extension name. This allows manual pages with the same title to
coexist in the same manual page hierarchy and section without sharing the
same filename. It also provides a further mechanism for man to select
the correct manual page.

manual page hierarchy
A directory tree divided into manual page sections, each containing a
collection of manual pages.

cat page hierarchy
A directory tree divided into cat page sections, each containing a col-
lection of cat pages.

traditional cat page hierarchy
The same location as the manual page hierarchy.

alternate cat page hierarchy
A separate location to that of the traditional cat page hierarchy.

traditional cat page
A cat page located in a traditional cat page hierarchy.

alternate cat page
A cat page located in an alternate cat page hierarchy.

Contents

1. Introduction ........................................................ 1
1.1 man-db ......................................................... 1
1.1.1 The concept ............................................. 1
1.2 The manual page system ......................................... 2
1.3 Sections of the manual ......................................... 2
1.4 The format of manual pages ..................................... 3
1.5 Arguments to configure ......................................... 3

2. The specifics of Sections ........................................... 5
2.1 Package specific manual page sections .......................... 5
2.2 Selecting a section type ....................................... 5
2.2.1 Specifying a section .................................... 5
2.2.2 Specifying an extension ................................. 6

3. Filesystem structure ................................................ 7
3.1 Manual page hierarchies ........................................ 7
3.2 Setting the MANPATH ............................................ 7
3.3 Determination of the internal manpath .......................... 8
3.4 Other OS's manual pages ........................................ 8
3.5 NLS manual pages ............................................... 9
3.5.1 ISO 8859-1 (latin1) manual pages ........................ 11
3.5.2 Displaying non-ASCII characters on a Linux virtual
terminal ....................................................... 11
3.5.3 Viewing ASCII pages formatted for latin1 output device
................................................................ 11
3.6 Cat pages ...................................................... 12
3.7 Cat page hierarchies ........................................... 12
3.8 Local cat page directory caches ................................ 13

4. Compression ......................................................... 14
4.1 Compressed manual pages ........................................ 14
4.2 Compressed cat pages ........................................... 14
4.2.1 Stray cats .............................................. 14

5. Formatting .......................................................... 16
5.1 GROFF .......................................................... 16
5.2 Devices ........................................................ 16
5.3 Macros ......................................................... 16
5.4 Pre-format processors (pre-processors) ......................... 17
5.5 Format scripts ................................................. 18

6. The index database caches ........................................... 19
6.1 index database location ........................................ 19
6.1.1 Manual hierarchies with no index database ............... 19
6.1.2 User manual page hierarchies ............................ 19
6.2 Contents of an index database .................................. 19
6.2.1 Favouring stray cats .................................... 21
6.2.2 Accessdb ................................................ 21
6.2.3 Example database ........................................ 21
6.3 Database types ................................................. 22

6.4 Limitations .................................................... 22
6.5 Sharing databases in a heterogeneous environment ............... 23

7. Miscellaneous ....................................................... 24
7.1 Modes of operation ............................................. 24
7.2 NFS root squash ................................................ 25
7.3 NLS message catalogues ......................................... 26
7.4 Credits ........................................................ 26

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