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Ubuntu Policy Manual
Chapter 11 - Customized programs


11.1 Architecture specification strings

If a program needs to specify an architecture specification string in some place, it should select one of the strings provided by dpkg-architecture -L. The strings are in the format os-arch, though the OS part is sometimes elided, as when the OS is Linux.[77]

Note that we don't want to use arch-debian-linux to apply to the rule architecture-vendor-os since this would make our programs incompatible with other Linux distributions. We also don't use something like arch-unknown-linux, since the unknown does not look very good.


11.2 Daemons

The configuration files /etc/services, /etc/protocols, and /etc/rpc are managed by the netbase package and must not be modified by other packages.

If a package requires a new entry in one of these files, the maintainer should get in contact with the netbase maintainer, who will add the entries and release a new version of the netbase package.

The configuration file /etc/inetd.conf must not be modified by the package's scripts except via the update-inetd script or the DebianNet.pm Perl module. See their documentation for details on how to add entries.

If a package wants to install an example entry into /etc/inetd.conf, the entry must be preceded with exactly one hash character (#). Such lines are treated as "commented out by user" by the update-inetd script and are not changed or activated during package updates.


11.3 Using pseudo-ttys and modifying wtmp, utmp and lastlog

Some programs need to create pseudo-ttys. This should be done using Unix98 ptys if the C library supports it. The resulting program must not be installed setuid root, unless that is required for other functionality.

The files /var/run/utmp, /var/log/wtmp and /var/log/lastlog must be installed writable by group utmp. Programs which need to modify those files must be installed setgid utmp.


11.4 Editors and pagers

Some programs have the ability to launch an editor or pager program to edit or display a text document. Since there are lots of different editors and pagers available in the Ubuntu distribution, the system administrator and each user should have the possibility to choose their preferred editor and pager.

In addition, every program should choose a good default editor/pager if none is selected by the user or system administrator.

Thus, every program that launches an editor or pager must use the EDITOR or PAGER environment variable to determine the editor or pager the user wishes to use. If these variables are not set, the programs /usr/bin/editor and /usr/bin/pager should be used, respectively.

These two files are managed through the dpkg "alternatives" mechanism. Thus every package providing an editor or pager must call the update-alternatives script to register these programs.

If it is very hard to adapt a program to make use of the EDITOR or PAGER variables, that program may be configured to use /usr/bin/sensible-editor and /usr/bin/sensible-pager as the editor or pager program respectively. These are two scripts provided in the Ubuntu base system that check the EDITOR and PAGER variables and launch the appropriate program, and fall back to /usr/bin/editor and /usr/bin/pager if the variable is not set.

A program may also use the VISUAL environment variable to determine the user's choice of editor. If it exists, it should take precedence over EDITOR. This is in fact what /usr/bin/sensible-editor does.

It is not required for a package to depend on editor and pager, nor is it required for a package to provide such virtual packages.[78]


11.5 Web servers and applications

This section describes the locations and URLs that should be used by all web servers and web applications in the Ubuntu system.

  1. Cgi-bin executable files are installed in the directory

         /usr/lib/cgi-bin/cgi-bin-name
    

    and should be referred to as

         http://localhost/cgi-bin/cgi-bin-name
    
  1. Access to HTML documents

    HTML documents for a package are stored in /usr/share/doc/package and can be referred to as

         http://localhost/doc/package/filename
    

    The web server should restrict access to the document tree so that only clients on the same host can read the documents. If the web server does not support such access controls, then it should not provide access at all, or ask about providing access during installation.

  1. Access to images

    It is recommended that images for a package be stored in /usr/share/images/package and may be referred to through an alias /images/ as

                           http://localhost/images/<package>/<filename>
    
  1. Web Document Root

    Web Applications should try to avoid storing files in the Web Document Root. Instead they should use the /usr/share/doc/package directory for documents and register the Web Application via the doc-base package. If access to the web document root is unavoidable then use

         /var/www
    

    as the Document Root. This might be just a symbolic link to the location where the system administrator has put the real document root.

  1. Providing httpd and/or httpd-cgi

    All web servers should provide the virtual package httpd. If a web server has CGI support it should provide httpd-cgi additionally.

    All web applications which do not contain CGI scripts should depend on httpd, all those web applications which do contain CGI scripts, should depend on httpd-cgi.


11.6 Mail transport, delivery and user agents

Ubuntu packages which process electronic mail, whether mail user agents (MUAs) or mail transport agents (MTAs), must ensure that they are compatible with the configuration decisions below. Failure to do this may result in lost mail, broken From: lines, and other serious brain damage!

The mail spool is /var/mail and the interface to send a mail message is /usr/sbin/sendmail (as per the FHS). On older systems, the mail spool may be physically located in /var/spool/mail, but all access to the mail spool should be via the /var/mail symlink. The mail spool is part of the base system and not part of the MTA package.

All Ubuntu MUAs, MTAs, MDAs and other mailbox accessing programs (such as IMAP daemons) must lock the mailbox in an NFS-safe way. This means that fcntl() locking must be combined with dot locking. To avoid deadlocks, a program should use fcntl() first and dot locking after this, or alternatively implement the two locking methods in a non blocking way[79]. Using the functions maillock and mailunlock provided by the liblockfile*[80] packages is the recommended way to realize this.

Mailboxes are generally either mode 600 and owned by user or mode 660 and owned by user:mail[81]. The local system administrator may choose a different permission scheme; packages should not make assumptions about the permission and ownership of mailboxes unless required (such as when creating a new mailbox). A MUA may remove a mailbox (unless it has nonstandard permissions) in which case the MTA or another MUA must recreate it if needed.

The mail spool is 2775 root:mail, and MUAs should be setgid mail to do the locking mentioned above (and must obviously avoid accessing other users' mailboxes using this privilege).

/etc/aliases is the source file for the system mail aliases (e.g., postmaster, usenet, etc.), it is the one which the sysadmin and postinst scripts may edit. After /etc/aliases is edited the program or human editing it must call newaliases. All MTA packages must come with a newaliases program, even if it does nothing, but older MTA packages did not do this so programs should not fail if newaliases cannot be found. Note that because of this, all MTA packages must have Provides, Conflicts and Replaces: mail-transport-agent control file fields.

The convention of writing forward to address in the mailbox itself is not supported. Use a .forward file instead.

The rmail program used by UUCP for incoming mail should be /usr/sbin/rmail. Likewise, rsmtp, for receiving batch-SMTP-over-UUCP, should be /usr/sbin/rsmtp if it is supported.

If your package needs to know what hostname to use on (for example) outgoing news and mail messages which are generated locally, you should use the file /etc/mailname. It will contain the portion after the username and @ (at) sign for email addresses of users on the machine (followed by a newline).

Such a package should check for the existence of this file when it is being configured. If it exists, it should be used without comment, although an MTA's configuration script may wish to prompt the user even if it finds that this file exists. If the file does not exist, the package should prompt the user for the value (preferably using debconf) and store it in /etc/mailname as well as using it in the package's configuration. The prompt should make it clear that the name will not just be used by that package. For example, in this situation the inn package could say something like:

     Please enter the "mail name" of your system.  This is the
     hostname portion of the address to be shown on outgoing
     news and mail messages.  The default is
     syshostname, your system's host name.  Mail
     name ["syshostname"]:

where syshostname is the output of hostname --fqdn.


11.7 News system configuration

All the configuration files related to the NNTP (news) servers and clients should be located under /etc/news.

There are some configuration issues that apply to a number of news clients and server packages on the machine. These are:

/etc/news/organization

A string which should appear as the organization header for all messages posted by NNTP clients on the machine

/etc/news/server

Contains the FQDN of the upstream NNTP server, or localhost if the local machine is an NNTP server.

Other global files may be added as required for cross-package news configuration.


11.8 Programs for the X Window System


11.8.1 Providing X support and package priorities

Programs that can be configured with support for the X Window System must be configured to do so and must declare any package dependencies necessary to satisfy their runtime requirements when using the X Window System. If such a package is of higher priority than the X packages on which it depends, it is required that either the X-specific components be split into a separate package, or that an alternative version of the package, which includes X support, be provided, or that the package's priority be lowered.


11.8.2 Packages providing an X server

Packages that provide an X server that, directly or indirectly, communicates with real input and display hardware should declare in their control data that they provide the virtual package xserver.[82]


11.8.3 Packages providing a terminal emulator

Packages that provide a terminal emulator for the X Window System which meet the criteria listed below should declare in their control data that they provide the virtual package x-terminal-emulator. They should also register themselves as an alternative for /usr/bin/x-terminal-emulator, with a priority of 20.

To be an x-terminal-emulator, a program must:


11.8.4 Packages providing a window manager

Packages that provide a window manager should declare in their control data that they provide the virtual package x-window-manager. They should also register themselves as an alternative for /usr/bin/x-window-manager, with a priority calculated as follows:


11.8.5 Packages providing fonts

Packages that provide fonts for the X Window System[84] must do a number of things to ensure that they are both available without modification of the X or font server configuration, and that they do not corrupt files used by other font packages to register information about themselves.

  1. Fonts of any type supported by the X Window System must be in a separate binary package from any executables, libraries, or documentation (except that specific to the fonts shipped, such as their license information). If one or more of the fonts so packaged are necessary for proper operation of the package with which they are associated the font package may be Recommended; if the fonts merely provide an enhancement, a Suggests relationship may be used. Packages must not Depend on font packages.[85]

  1. BDF fonts must be converted to PCF fonts with the bdftopcf utility (available in the xfonts-utils package, gzipped, and placed in a directory that corresponds to their resolution:

  1. Type 1 fonts must be placed in /usr/share/fonts/X11/Type1/. If font metric files are available, they must be placed here as well.

  1. Subdirectories of /usr/share/fonts/X11/ other than those listed above must be neither created nor used. (The PEX, CID, Speedo, and cyrillic directories are excepted for historical reasons, but installation of files into these directories remains discouraged.)

  1. Font packages may, instead of placing files directly in the X font directories listed above, provide symbolic links in that font directory pointing to the files' actual location in the filesystem. Such a location must comply with the FHS.

  1. Font packages should not contain both 75dpi and 100dpi versions of a font. If both are available, they should be provided in separate binary packages with -75dpi or -100dpi appended to the names of the packages containing the corresponding fonts.

  1. Fonts destined for the misc subdirectory should not be included in the same package as 75dpi or 100dpi fonts; instead, they should be provided in a separate package with -misc appended to its name.

  1. Font packages must not provide the files fonts.dir, fonts.alias, or fonts.scale in a font directory:

  1. Font packages must declare a dependency on xfonts-utils in their control data.

  1. Font packages that provide one or more fonts.scale files as described above must invoke update-fonts-scale on each directory into which they installed fonts before invoking update-fonts-dir on that directory. This invocation must occur in both the postinst (for all arguments) and postrm (for all arguments except upgrade) scripts.

  1. Font packages that provide one or more fonts.alias files as described above must invoke update-fonts-alias on each directory into which they installed fonts. This invocation must occur in both the postinst (for all arguments) and postrm (for all arguments except upgrade) scripts.

  1. Font packages must invoke update-fonts-dir on each directory into which they installed fonts. This invocation must occur in both the postinst (for all arguments) and postrm (for all arguments except upgrade) scripts.

  1. Font packages must not provide alias names for the fonts they include which collide with alias names already in use by fonts already packaged.

  1. Font packages must not provide fonts with the same XLFD registry name as another font already packaged.


11.8.6 Application defaults files

Application defaults files must be installed in the directory /etc/X11/app-defaults/ (use of a localized subdirectory of /etc/X11/ as described in the X Toolkit Intrinsics - C Language Interface manual is also permitted). They must be registered as conffiles or handled as configuration files.

Customization of programs' X resources may also be supported with the provision of a file with the same name as that of the package placed in the /etc/X11/Xresources/ directory, which must registered as a conffile or handled as a configuration file.[86]


11.8.7 Installation directory issues

Packages using the X Window System should not be configured to install files under the /usr/X11R6/ directory. The /usr/X11R6/ directory hierarchy should be regarded as obsolete.

Programs that use GNU autoconf and automake are usually easily configured at compile time to use /usr/ instead of /usr/X11R6/, and this should be done whenever possible. Configuration files for window managers and display managers should be placed in a subdirectory of /etc/X11/ corresponding to the package name due to these programs' tight integration with the mechanisms of the X Window System. Application-level programs should use the /etc/ directory unless otherwise mandated by policy.

The installation of files into subdirectories of /usr/X11R6/include/X11/ and /usr/X11R6/lib/X11/ is now prohibited; package maintainers should determine if subdirectories of /usr/lib/ and /usr/share/ can be used instead.

Packages should install any relevant files into the directories /usr/include/X11/ and /usr/lib/X11/, but if they do so, they must pre-depend on x11-common (>= 1:7.0.0)[87]


11.8.8 The OSF/Motif and OpenMotif libraries

Programs that require the non-DFSG-compliant OSF/Motif or OpenMotif libraries[88] should be compiled against and tested with LessTif (a free re-implementation of Motif) instead. If the maintainer judges that the program or programs do not work sufficiently well with LessTif to be distributed and supported, but do so when compiled against Motif, then two versions of the package should be created; one linked statically against Motif and with -smotif appended to the package name, and one linked dynamically against Motif and with -dmotif appended to the package name.

Both Motif-linked versions are dependent upon non-DFSG-compliant software and thus cannot be uploaded to the main distribution; if the software is itself DFSG-compliant it may be uploaded to the contrib distribution. While known existing versions of Motif permit unlimited redistribution of binaries linked against the library (whether statically or dynamically), it is the package maintainer's responsibility to determine whether this is permitted by the license of the copy of Motif in their possession.


11.8.9 Icon caching

Ubuntu: Packages that provide icons in a subdirectory of /usr/share/icons must invoke update-icon-caches on each directory into which they installed icons. This invocation must occur in both the postinst (for all arguments) and postrm (for all arguments) scripts[89]. Doing this allows GTK+ to make use of the icon cache for efficiency gains, while ensuring that the cache does not get out of date and cause problems for some applications.

If update-icon-caches is not installed, this invocation may safely be skipped. No additional dependency is necessary.


11.9 Perl programs and modules

Perl programs and modules should follow the current Perl policy.

The Perl policy can be found in the perl-policy files in the debian-policy package. It is also available from the Debian web mirrors at /doc/packaging-manuals/perl-policy/.


11.10 Emacs lisp programs

Please refer to the "Debian Emacs Policy" for details of how to package emacs lisp programs.

The Emacs policy is available in debian-emacs-policy.gz of the emacsen-common package. It is also available from the Debian web mirrors at /doc/packaging-manuals/debian-emacs-policy.


11.11 Games

The permissions on /var/games are mode 755, owner root and group root.

Each game decides on its own security policy.

Games which require protected, privileged access to high-score files, saved games, etc., may be made set-group-id (mode 2755) and owned by root:games, and use files and directories with appropriate permissions (770 root:games, for example). They must not be made set-user-id, as this causes security problems. (If an attacker can subvert any set-user-id game they can overwrite the executable of any other, causing other players of these games to run a Trojan horse program. With a set-group-id game the attacker only gets access to less important game data, and if they can get at the other players' accounts at all it will take considerably more effort.)

Some packages, for example some fortune cookie programs, are configured by the upstream authors to install with their data files or other static information made unreadable so that they can only be accessed through set-id programs provided. You should not do this in an Ubuntu package: anyone can download the .deb file and read the data from it, so there is no point making the files unreadable. Not making the files unreadable also means that you don't have to make so many programs set-id, which reduces the risk of a security hole.

As described in the FHS, binaries of games should be installed in the directory /usr/games. This also applies to games that use the X Window System. Manual pages for games (X and non-X games) should be installed in /usr/share/man/man6.


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Ubuntu Policy Manual

version 3.8.2.0ubuntu1, 2009-06-19

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