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dpkg-maintscript-helper(1)	  dpkg suite	    dpkg-maintscript-helper(1)

NAME
       dpkg-maintscript-helper	-  works  around  known	 dpkg  limitations  in
       maintainer scripts

SYNOPSIS
       dpkg-maintscript-helper	 command   [parameter...]   --	 maint-script-
       parameter...

COMMANDS AND PARAMETERS
       supports	command

       rm_conffile conffile [prior-version [package]]

       mv_conffile old-conffile	new-conffile [prior-version [package]]

       symlink_to_dir pathname old-target [prior-version [package]]

       dir_to_symlink pathname new-target [prior-version [package]]

DESCRIPTION
       This program is designed	to be run within maintainer scripts to achieve
       some tasks that dpkg can't (yet)	 handle	 natively  either  because  of
       design decisions	or due to current limitations.

       Many of those tasks require coordinated actions from several maintainer
       scripts (preinst, postinst, prerm, postrm). To avoid mistakes the  same
       call  simply  needs  to	be  put	 in  all  scripts and the program will
       automatically adapt its behaviour based	on  the	 environment  variable
       DPKG_MAINTSCRIPT_NAME  and on the maintainer scripts arguments that you
       have to forward after a double hyphen.

COMMON PARAMETERS
       prior-version
	      Defines the latest version of the	package	whose  upgrade	should
	      trigger  the  operation.	It  is	important  to calculate	prior-
	      version correctly	so that	the operations are correctly performed
	      even  if	the  user rebuilt the package with a local version. If
	      prior-version is empty or	omitted, then the operation  is	 tried
	      on  every	upgrade	(note: it's safer to give the version and have
	      the operation tried only once).

	      If the conffile has not been shipped for several	versions,  and
	      you  are	now  modifying	the maintainer scripts to clean	up the
	      obsolete file, prior-version should be based on the  version  of
	      the package that you are now preparing, not the first version of
	      the package that lacked the conffile. This applies to all	 other
	      actions in the same way.

	      For  example,  for  a  conffile  removed	in  version 2.0-1 of a
	      package, prior-version should be set to 2.0-1~. This will	 cause
	      the conffile to be removed even if the user rebuilt the previous
	      version 1.0-1 as 1.0-1local1. Or a package switching a path from
	      a	 symlink (shipped in version 1.0-1) to a directory (shipped in
	      version 2.0-1), but only performing the  actual  switch  in  the
	      maintainer scripts in version 3.0-1, should set prior-version to
	      3.0-1~.

       package
	      The package name owning the pathname(s).	When  the  package  is
	      "Multi-Arch:  same" this parameter must include the architecture
	      qualifier,  otherwise  it	 should	 not   usually	 include   the
	      architecture  qualifier  (as  it would disallow cross-grades, or
	      switching	from being architecture	specific to  architecture  all
	      or  vice	versa).	  If  the  parameter  is empty or omitted, the
	      DPKG_MAINTSCRIPT_PACKAGE and  DPKG_MAINTSCRIPT_ARCH  environment
	      variables	 (as  set by dpkg when running the maintainer scripts)
	      will be used to generate an arch-qualified package name.

       --     All  the	parameters  of	the  maintainer	 scripts  have	to  be
	      forwarded	to the program after --.

CONFFILE RELATED TASKS
       When upgrading a	package, dpkg will not automatically remove a conffile
       (a configuration	file for which dpkg should preserve user  changes)  if
       it is not present in the	newer version. There are two principal reasons
       for this; the first is that  the	 conffile  could've  been  dropped  by
       accident	 and  the  next	 version could restore it, users wouldn't want
       their  changes  thrown  away.  The  second  is  to  allow  packages  to
       transition  files  from a dpkg-maintained conffile to a file maintained
       by the package's	maintainer scripts, usually with a tool	 like  debconf
       or ucf.

       This  means  that  if  a	 package  is  intended	to  rename or remove a
       conffile, it must explicitly do so and dpkg-maintscript-helper  can  be
       used  to	 implement  graceful  deletion	and moving of conffiles	within
       maintainer scripts.

   Removing a conffile
       If a conffile is	completely removed, it should be  removed  from	 disk,
       unless the user has modified it.	If there are local modifications, they
       should be preserved. If the package upgrades aborts, the	newly obsolete
       conffile	should not disappear.

       All  of	this  is implemented by	putting	the following shell snippet in
       the preinst, postinst and postrm	maintainer scripts:

	   dpkg-maintscript-helper rm_conffile \
	       conffile	prior-version package -- "$@"

       conffile	is the filename	of the conffile	to remove.

       Current implementation: in the preinst, it checks if the	 conffile  was
       modified	  and  renames	it  either  to	conffile.dpkg-remove  (if  not
       modified) or to conffile.dpkg-backup (if	modified).  In	the  postinst,
       the  latter file	is renamed to conffile.dpkg-bak	and kept for reference
       as it contains user modifications but the former	will  be  removed.  If
       the   package  upgrade  aborts,	the  postrm  reinstalls	 the  original
       conffile. During	purge, the postrm will also delete the .dpkg-bak  file
       kept up to now.

   Renaming a conffile
       If  a  conffile is moved	from one location to another, you need to make
       sure you	move across any	changes	the user has made.  This  may  seem  a
       simple  change to the preinst script at first, however that will	result
       in the user being prompted by dpkg to approve the conffile  edits  even
       though they are not responsible of them.

       Graceful	 renaming  can	be  implemented	by putting the following shell
       snippet in the preinst, postinst	and postrm maintainer scripts:

	   dpkg-maintscript-helper mv_conffile \
	       old-conffile new-conffile prior-version package -- "$@"

       old-conffile and	new-conffile are the old and new name of the  conffile
       to rename.

       Current	implementation:	 the  preinst  checks if the conffile has been
       modified, if yes	it's left on place  otherwise  it's  renamed  to  old-
       conffile.dpkg-remove.  On  configuration,  the  postinst	 removes  old-
       conffile.dpkg-remove and	renames	old-conffile to	new-conffile  if  old-
       conffile	is still available. On abort-upgrade/abort-install, the	postrm
       renames old-conffile.dpkg-remove	back to	old-conffile if	required.

SYMLINK	AND DIRECTORY SWITCHES
       When upgrading a	package, dpkg will not automatically switch a  symlink
       to a directory or vice-versa. Downgrades	are not	supported and the path
       will be left as is.

   Switching a symlink to directory
       If a symlink is switched	to a real directory, you  need	to  make  sure
       before  unpacking  that	the symlink is removed.	This may seem a	simple
       change to the preinst script at first, however that will	result in some
       problems	 in  case  of admin local customization	of the symlink or when
       downgrading the package.

       Graceful	renaming can be	implemented by	putting	 the  following	 shell
       snippet in the preinst, postinst	and postrm maintainer scripts:

	   dpkg-maintscript-helper symlink_to_dir \
	       pathname	old-target prior-version package -- "$@"

       pathname	 is  the  absolute name	of the old symlink (the	path will be a
       directory at the	end of the installation) and old-target	is the	target
       name  of	 the  former symlink at	pathname. It can either	be absolute or
       relative	to the directory containing pathname.

       Current implementation: the preinst checks if the  symlink  exists  and
       points  to  old-target,	if not then it's left in place,	otherwise it's
       renamed to pathname.dpkg-backup.	On configuration, the postinst removes
       pathname.dpkg-backup  if	 pathname.dpkg-backup  is  still a symlink. On
       abort-upgrade/abort-install, the	 postrm	 renames  pathname.dpkg-backup
       back to pathname	if required.

   Switching a directory to symlink
       If  a  real  directory  is switched to a	symlink, you need to make sure
       before unpacking	that the directory is removed. This may	seem a	simple
       change to the preinst script at first, however that will	result in some
       problems	in case	the directory contains conffiles, pathnames  owned  by
       other  packages,	 locally  created  pathnames,  or when downgrading the
       package.

       Graceful	switching can be implemented by	putting	 the  following	 shell
       snippet in the preinst, postinst	and postrm maintainer scripts:

	   dpkg-maintscript-helper dir_to_symlink \
	       pathname	new-target prior-version package -- "$@"

       pathname	 is the	absolute name of the old directory (the	path will be a
       symlink at the end of the installation) and new-target is the target of
       the  new	 symlink at pathname. It can either be absolute	or relative to
       the directory containing	pathname.

       Current implementation: the preinst checks  if  the  directory  exists,
       does  not  contain  conffiles,  pathnames  owned	 by other packages, or
       locally created pathnames, if not then it's left	 in  place,  otherwise
       it's  renamed  to  pathname.dpkg-backup,	and an empty staging directory
       named pathname is created, marked with a	file so	that  dpkg  can	 track
       it.   On	  configuration,   the	 postinst   finishes   the  switch  if
       pathname.dpkg-backup is still a directory and pathname is  the  staging
       directory;  it removes the staging directory mark file, moves the newly
       created files inside the	staging	directory to the symlink  target  new-
       target/,	 replaces  the	now  empty  staging  directory pathname	with a
       symlink	 to   new-target,   and	  removes   pathname.dpkg-backup.   On
       abort-upgrade/abort-install,  the  postrm  renames pathname.dpkg-backup
       back to pathname	if required.

INTEGRATION IN PACKAGES
       When using a packaging helper, please check  if	it  has	 native	 dpkg-
       maintscript-helper  integration,	which might make your life easier. See
       for example dh_installdeb(1).

       Given that dpkg-maintscript-helper is used in  the  preinst,  using  it
       unconditionally	requires  a pre-dependency to ensure that the required
       version of dpkg has been	unpacked before. The required version  depends
       on  the	command	 used, for rm_conffile and mv_conffile it is 1.15.7.2,
       for symlink_to_dir and dir_to_symlink it	is 1.17.14:

	   Pre-Depends:	dpkg (>= 1.17.14)

       But in many cases the operation done by the program is not critical for
       the  package,  and  instead  of	using a	pre-dependency we can call the
       program only if we know that the	required command is supported  by  the
       currently installed dpkg:

	   if dpkg-maintscript-helper supports command;	then
	       dpkg-maintscript-helper command ...
	   fi

       The  command  supports  will  return  0	on  success,  1	otherwise. The
       supports	command	will check if the environment variables	as set by dpkg
       and  required by	the script are present,	and will consider it a failure
       in case the environment is not sufficient.

ENVIRONMENT
       DPKG_COLORS
	      Sets the color mode (since dpkg 1.19.1).	The currently accepted
	      values are: auto (default), always and never.

SEE ALSO
       dh_installdeb(1).

1.19.7				  2019-06-03	    dpkg-maintscript-helper(1)

NAME | SYNOPSIS | COMMANDS AND PARAMETERS | DESCRIPTION | COMMON PARAMETERS | CONFFILE RELATED TASKS | SYMLINK AND DIRECTORY SWITCHES | INTEGRATION IN PACKAGES | ENVIRONMENT | SEE ALSO

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