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

6       dpkg-maintscript-helper  -  works  around  known  dpkg  limitations  in
7       maintainer scripts
8

SYNOPSIS

10       dpkg-maintscript-helper   command   [parameter...]   --   maint-script-
11       parameter...
12

COMMANDS AND PARAMETERS

14       supports command
15
16       rm_conffile conffile [prior-version [package]]
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18       mv_conffile old-conffile new-conffile [prior-version [package]]
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20       symlink_to_dir pathname old-target [prior-version [package]]
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22       dir_to_symlink pathname new-target [prior-version [package]]
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DESCRIPTION

25       This program is designed to be run within maintainer scripts to achieve
26       some tasks that dpkg can't (yet)  handle  natively  either  because  of
27       design decisions or due to current limitations.
28
29       Many of those tasks require coordinated actions from several maintainer
30       scripts (preinst, postinst, prerm, postrm). To avoid mistakes the  same
31       call  simply  needs  to  be  put  in  all  scripts and the program will
32       automatically adapt its behaviour based  on  the  environment  variable
33       DPKG_MAINTSCRIPT_NAME  and on the maintainer scripts arguments that you
34       have to forward after a double hyphen.
35

COMMON PARAMETERS

37       prior-version
38              Defines the latest version of the package whose  upgrade  should
39              trigger  the  operation.  It  is  important  to calculate prior-
40              version correctly so that the operations are correctly performed
41              even  if  the  user rebuilt the package with a local version. If
42              prior-version is empty or omitted, then the operation  is  tried
43              on  every upgrade (note: it's safer to give the version and have
44              the operation tried only once).
45
46              If the conffile has not been shipped for several  versions,  and
47              you  are  now  modifying  the maintainer scripts to clean up the
48              obsolete file, prior-version should be based on the  version  of
49              the package that you are now preparing, not the first version of
50              the package that lacked the conffile. This applies to all  other
51              actions in the same way.
52
53              For  example,  for  a  conffile  removed  in  version 2.0-1 of a
54              package, prior-version should be set to 2.0-1~. This will  cause
55              the conffile to be removed even if the user rebuilt the previous
56              version 1.0-1 as 1.0-1local1. Or a package switching a path from
57              a  symlink (shipped in version 1.0-1) to a directory (shipped in
58              version 2.0-1), but only performing the  actual  switch  in  the
59              maintainer scripts in version 3.0-1, should set prior-version to
60              3.0-1~.
61
62       package
63              The package name. When the package is  “Multi-Arch:  same”  this
64              parameter  must include the architecture qualifier, otherwise it
65              should not usually include the  architecture  qualifier  (as  it
66              would   disallow   cross-grades,   or   switching   from   being
67              architecture specific to architecture all or  vice  versa).   If
68              the  parameter is empty or omitted, the DPKG_MAINTSCRIPT_PACKAGE
69              and DPKG_MAINTSCRIPT_ARCH environment variables (as set by dpkg)
70              will be used to generate an arch-qualified package name.
71
72       --     All  the  parameters  of  the  maintainer  scripts  have  to  be
73              forwarded to the program after --.
74
76       When upgrading a package, dpkg will not automatically remove a conffile
77       (a  configuration  file for which dpkg should preserve user changes) if
78       it is not present in the newer version. There are two principal reasons
79       for  this;  the  first  is  that  the conffile could've been dropped by
80       accident and the next version could restore  it,  users  wouldn't  want
81       their  changes  thrown  away.  The  second  is  to  allow  packages  to
82       transition files from a dpkg-maintained conffile to a  file  maintained
83       by  the  package's maintainer scripts, usually with a tool like debconf
84       or ucf.
85
86       This means that if  a  package  is  intended  to  rename  or  remove  a
87       conffile,  it  must explicitly do so and dpkg-maintscript-helper can be
88       used to implement graceful deletion  and  moving  of  conffiles  within
89       maintainer scripts.
90
91   Removing a conffile
92       If  a  conffile  is completely removed, it should be removed from disk,
93       unless the user has modified it. If there are local modifications, they
94       should be preserved. If the package upgrades aborts, the newly obsolete
95       conffile should not disappear.
96
97       All of this is implemented by putting the following  shell  snippet  in
98       the preinst, postinst and postrm maintainer scripts:
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100           dpkg-maintscript-helper rm_conffile \
101               conffile prior-version package -- "$@"
102
103       conffile is the filename of the conffile to remove.
104
105       Current  implementation:  in the preinst, it checks if the conffile was
106       modified  and  renames  it  either  to  conffile.dpkg-remove  (if   not
107       modified)  or  to  conffile.dpkg-backup (if modified). In the postinst,
108       the latter file is renamed to conffile.dpkg-bak and kept for  reference
109       as  it  contains  user modifications but the former will be removed. If
110       the  package  upgrade  aborts,  the  postrm  reinstalls  the   original
111       conffile.  During purge, the postrm will also delete the .dpkg-bak file
112       kept up to now.
113
114   Renaming a conffile
115       If a conffile is moved from one location to another, you need  to  make
116       sure  you  move  across  any changes the user has made. This may seem a
117       simple change to the preinst script at first, however that will  result
118       in  the  user being prompted by dpkg to approve the conffile edits even
119       though they are not responsible of them.
120
121       Graceful renaming can be implemented by  putting  the  following  shell
122       snippet in the preinst, postinst and postrm maintainer scripts:
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124           dpkg-maintscript-helper mv_conffile \
125               old-conffile new-conffile prior-version package -- "$@"
126
127       old-conffile  and new-conffile are the old and new name of the conffile
128       to rename.
129
130       Current implementation: the preinst checks if  the  conffile  has  been
131       modified,  if  yes  it's  left  on place otherwise it's renamed to old-
132       conffile.dpkg-remove.  On  configuration,  the  postinst  removes  old-
133       conffile.dpkg-remove  and  renames old-conffile to new-conffile if old-
134       conffile is still available. On abort-upgrade/abort-install, the postrm
135       renames old-conffile.dpkg-remove back to old-conffile if required.
136
138       When  upgrading a package, dpkg will not automatically switch a symlink
139       to a directory or vice-versa. Downgrades are not supported and the path
140       will be left as is.
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142   Switching a symlink to directory
143       If  a  symlink  is  switched to a real directory, you need to make sure
144       before unpacking that the symlink is removed. This may  seem  a  simple
145       change to the preinst script at first, however that will result in some
146       problems in case of admin local customization of the  symlink  or  when
147       downgrading the package.
148
149       Graceful  renaming  can  be  implemented by putting the following shell
150       snippet in the preinst, postinst and postrm maintainer scripts:
151
152           dpkg-maintscript-helper symlink_to_dir \
153               pathname old-target prior-version package -- "$@"
154
155       pathname is the absolute name of the old symlink (the path  will  be  a
156       directory  at the end of the installation) and old-target is the target
157       name of the former symlink at pathname. It can either  be  absolute  or
158       relative to the directory containing pathname.
159
160       Current  implementation:  the  preinst checks if the symlink exists and
161       points to old-target, if not then it's left in  place,  otherwise  it's
162       renamed to pathname.dpkg-backup. On configuration, the postinst removes
163       pathname.dpkg-backup if pathname.dpkg-backup is  still  a  symlink.  On
164       abort-upgrade/abort-install,  the  postrm  renames pathname.dpkg-backup
165       back to pathname if required.
166
167   Switching a directory to symlink
168       If a real directory is switched to a symlink, you  need  to  make  sure
169       before  unpacking that the directory is removed. This may seem a simple
170       change to the preinst script at first, however that will result in some
171       problems  in  case the directory contains conffiles, pathnames owned by
172       other packages, locally created  pathnames,  or  when  downgrading  the
173       package.
174
175       Graceful  switching  can  be implemented by putting the following shell
176       snippet in the preinst, postinst and postrm maintainer scripts:
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178           dpkg-maintscript-helper dir_to_symlink \
179               pathname new-target prior-version package -- "$@"
180
181       pathname is the absolute name of the old directory (the path will be  a
182       symlink at the end of the installation) and new-target is the target of
183       the new symlink at pathname. It can either be absolute or  relative  to
184       the directory containing pathname.
185
186       Current  implementation:  the  preinst  checks if the directory exists,
187       does not contain conffiles,  pathnames  owned  by  other  packages,  or
188       locally  created  pathnames,  if not then it's left in place, otherwise
189       it's renamed to pathname.dpkg-backup, and an  empty  staging  directory
190       named  pathname  is  created, marked with a file so that dpkg can track
191       it.  On  configuration,   the   postinst   finishes   the   switch   if
192       pathname.dpkg-backup  is  still a directory and pathname is the staging
193       directory; it removes the staging directory mark file, moves the  newly
194       created  files  inside the staging directory to the symlink target new-
195       target/, replaces the now  empty  staging  directory  pathname  with  a
196       symlink   to   new-target,   and   removes   pathname.dpkg-backup.   On
197       abort-upgrade/abort-install, the  postrm  renames  pathname.dpkg-backup
198       back to pathname if required.
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INTEGRATION IN PACKAGES

201       When  using  a  packaging  helper,  please check if it has native dpkg-
202       maintscript-helper integration, which might make your life easier.  See
203       for example dh_installdeb(1).
204
205       Given  that  dpkg-maintscript-helper  is  used in the preinst, using it
206       unconditionally requires a pre-dependency to ensure that  the  required
207       version  of dpkg has been unpacked before. The required version depends
208       on the command used, for rm_conffile and mv_conffile  it  is  1.15.7.2,
209       for symlink_to_dir and dir_to_symlink it is 1.17.14:
210
211           Pre-Depends: dpkg (>= 1.17.14)
212
213       But in many cases the operation done by the program is not critical for
214       the package, and instead of using a  pre-dependency  we  can  call  the
215       program  only  if we know that the required command is supported by the
216       currently installed dpkg:
217
218           if dpkg-maintscript-helper supports command; then
219               dpkg-maintscript-helper command ...
220           fi
221
222       The command supports  will  return  0  on  success,  1  otherwise.  The
223       supports command will check if the environment variables as set by dpkg
224       and required by the script are present, and will consider it a  failure
225       in case the environment is not sufficient.
226

SEE ALSO

228       dh_installdeb(1).
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2321.18.25                           2018-06-26        dpkg-maintscript-helper(1)
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