1dpkg-maintscript-helper(1) dpkg suite dpkg-maintscript-helper(1)
2
6 dpkg-maintscript-helper - works around known dpkg limitations in
7 maintainer scripts
8
10 dpkg-maintscript-helper command [parameter...] -- maint-script-
11 parameter...
12
14 supports command
15 rm_conffile conffile [prior-version [package]]
16 mv_conffile old-conffile new-conffile [prior-version [package]]
17 symlink_to_dir pathname old-target [prior-version [package]]
18 dir_to_symlink pathname new-target [prior-version [package]]
19
21 This program is designed to be run within maintainer scripts to achieve
22 some tasks that dpkg can't (yet) handle natively either because of
23 design decisions or due to current limitations.
24 Many of those tasks require coordinated actions from several maintainer
26 scripts (preinst, postinst, prerm, postrm). To avoid mistakes the same
27 call simply needs to be put in all scripts and the program will
28 automatically adapt its behaviour based on the environment variable
29 DPKG_MAINTSCRIPT_NAME and on the maintainer scripts arguments that you
30 have to forward after a double hyphen.
31
33 prior-version
34 Defines the latest version of the package whose upgrade should
35 trigger the operation. It is important to calculate prior-version
36 correctly so that the operations are correctly performed even if
37 the user rebuilt the package with a local version. If prior-version
38 is empty or omitted, then the operation is tried on every upgrade
39 (note: it's safer to give the version and have the operation tried
40 only once).
41 If the conffile has not been shipped for several versions, and you
43 are now modifying the maintainer scripts to clean up the obsolete
44 file, prior-version should be based on the version of the package
45 that you are now preparing, not the first version of the package
46 that lacked the conffile. This applies to all other actions in the
47 same way.
48 For example, for a conffile removed in version 2.0-1 of a package,
50 prior-version should be set to 2.0-1~. This will cause the conffile
51 to be removed even if the user rebuilt the previous version 1.0-1
52 as 1.0-1local1. Or a package switching a path from a symlink
53 (shipped in version 1.0-1) to a directory (shipped in version
54 2.0-1), but only performing the actual switch in the maintainer
55 scripts in version 3.0-1, should set prior-version to 3.0-1~.
56 package
58 The package name owning the pathname(s). When the package is
59 “Multi-Arch: same” this parameter must include the architecture
60 qualifier, otherwise it should not usually include the architecture
61 qualifier (as it would disallow cross-grades, or switching from
62 being architecture specific to architecture all or vice versa). If
63 the parameter is empty or omitted, the DPKG_MAINTSCRIPT_PACKAGE and
64 DPKG_MAINTSCRIPT_ARCH environment variables (as set by dpkg when
65 running the maintainer scripts) will be used to generate an arch-
66 qualified package name.
67 -- All the parameters of the maintainer scripts have to be forwarded
69 to the program after --.
70
72 When upgrading a package, dpkg will not automatically remove a conffile
73 (a configuration file for which dpkg should preserve user changes) if
74 it is not present in the newer version. There are two principal reasons
75 for this; the first is that the conffile could've been dropped by
76 accident and the next version could restore it, users wouldn't want
77 their changes thrown away. The second is to allow packages to
78 transition files from a dpkg-maintained conffile to a file maintained
79 by the package's maintainer scripts, usually with a tool like debconf
80 or ucf.
81 This means that if a package is intended to rename or remove a
83 conffile, it must explicitly do so and dpkg-maintscript-helper can be
84 used to implement graceful deletion and moving of conffiles within
85 maintainer scripts.
86 Removing a conffile
88 Note: This can be replaced in most cases by the "remove-on-upgrade"
89 flag in DEBIAN/conffiles (since dpkg 1.20.6), see deb-conffiles(5).
90 If a conffile is completely removed, it should be removed from disk,
92 unless the user has modified it. If there are local modifications, they
93 should be preserved. If the package upgrades aborts, the newly obsolete
94 conffile should not disappear.
95 All of this is implemented by putting the following shell snippet in
97 the preinst, postinst and postrm maintainer scripts:
98 dpkg-maintscript-helper rm_conffile \
101 conffile prior-version package -- "$@"
102 conffile is the filename of the conffile to remove.
104 Current implementation: in the preinst, it checks if the conffile was
106 modified and renames it either to conffile.dpkg-remove (if not
107 modified) or to conffile.dpkg-backup (if modified). In the postinst,
108 the latter file is renamed to conffile.dpkg-bak and kept for reference
109 as it contains user modifications but the former will be removed. If
110 the package upgrade aborts, the postrm reinstalls the original
111 conffile. During purge, the postrm will also delete the .dpkg-bak file
112 kept up to now.
113 Renaming a conffile
115 If a conffile is moved from one location to another, you need to make
116 sure you move across any changes the user has made. This may seem a
117 simple change to the preinst script at first, however that will result
118 in the user being prompted by dpkg to approve the conffile edits even
119 though they are not responsible of them.
120 Graceful renaming can be implemented by putting the following shell
122 snippet in the preinst, postinst and postrm maintainer scripts:
123 dpkg-maintscript-helper mv_conffile \
126 old-conffile new-conffile prior-version package -- "$@"
127 old-conffile and new-conffile are the old and new name of the conffile
129 to rename.
130 Current implementation: the preinst checks if the conffile has been
132 modified, if yes it's left on place otherwise it's renamed to old-
133 conffile.dpkg-remove. On configuration, the postinst removes old-
134 conffile.dpkg-remove and renames old-conffile to new-conffile if old-
135 conffile is still available. On abort-upgrade/abort-install, the postrm
136 renames old-conffile.dpkg-remove back to old-conffile if required.
137
139 When upgrading a package, dpkg will not automatically switch a symlink
140 to a directory or vice-versa. Downgrades are not supported and the path
141 will be left as is.
142 Note: The symlinks and directories created during these switches need
144 to be shipped in the new packages, or dpkg will not be able to remove
145 them on purge.
146 Switching a symlink to directory
148 If a symlink is switched to a real directory, you need to make sure
149 before unpacking that the symlink is removed. This may seem a simple
150 change to the preinst script at first, however that will result in some
151 problems in case of admin local customization of the symlink or when
152 downgrading the package.
153 Graceful renaming can be implemented by putting the following shell
155 snippet in the preinst, postinst and postrm maintainer scripts:
156 dpkg-maintscript-helper symlink_to_dir \
159 pathname old-target prior-version package -- "$@"
160 pathname is the absolute name of the old symlink (the path will be a
162 directory at the end of the installation) and old-target is the target
163 name of the former symlink at pathname. It can either be absolute or
164 relative to the directory containing pathname.
165 Current implementation: the preinst checks if the symlink exists and
167 points to old-target, if not then it's left in place, otherwise it's
168 renamed to pathname.dpkg-backup. On configuration, the postinst removes
169 pathname.dpkg-backup if pathname.dpkg-backup is still a symlink. On
170 abort-upgrade/abort-install, the postrm renames pathname.dpkg-backup
171 back to pathname if required.
172 Switching a directory to symlink
174 If a real directory is switched to a symlink, you need to make sure
175 before unpacking that the directory is removed. This may seem a simple
176 change to the preinst script at first, however that will result in some
177 problems in case the directory contains conffiles, pathnames owned by
178 other packages, locally created pathnames, or when downgrading the
179 package.
180 Graceful switching can be implemented by putting the following shell
182 snippet in the preinst, postinst and postrm maintainer scripts:
183 dpkg-maintscript-helper dir_to_symlink \
186 pathname new-target prior-version package -- "$@"
187 pathname is the absolute name of the old directory (the path will be a
189 symlink at the end of the installation) and new-target is the target of
190 the new symlink at pathname. It can either be absolute or relative to
191 the directory containing pathname.
192 Current implementation: the preinst checks if the directory exists,
194 does not contain conffiles, pathnames owned by other packages, or
195 locally created pathnames, if not then it's left in place, otherwise
196 it's renamed to pathname.dpkg-backup, and an empty staging directory
197 named pathname is created, marked with a file so that dpkg can track
198 it. On configuration, the postinst finishes the switch if
199 pathname.dpkg-backup is still a directory and pathname is the staging
200 directory; it removes the staging directory mark file, moves the newly
201 created files inside the staging directory to the symlink target new-
202 target/, replaces the now empty staging directory pathname with a
203 symlink to new-target, and removes pathname.dpkg-backup. On
204 abort-upgrade/abort-install, the postrm renames pathname.dpkg-backup
205 back to pathname if required.
206
208 When using a packaging helper, please check if it has native dpkg-
209 maintscript-helper integration, which might make your life easier. See
210 for example dh_installdeb(1).
211 Given that dpkg-maintscript-helper is used in the preinst, using it
213 unconditionally requires a pre-dependency to ensure that the required
214 version of dpkg has been unpacked before. The required version depends
215 on the command used, for rm_conffile and mv_conffile it is 1.15.7.2,
216 for symlink_to_dir and dir_to_symlink it is 1.17.14:
217 Pre-Depends: dpkg (>= 1.17.14)
219 But in many cases the operation done by the program is not critical for
221 the package, and instead of using a pre-dependency we can call the
222 program only if we know that the required command is supported by the
223 currently installed dpkg:
224 if dpkg-maintscript-helper supports command; then
227 dpkg-maintscript-helper command ...
228 fi
229 The command supports will return 0 on success, 1 otherwise. The
231 supports command will check if the environment variables as set by dpkg
232 and required by the script are present, and will consider it a failure
233 in case the environment is not sufficient.
234
236 DPKG_ROOT
237 If set, it will be used as the filesystem root directory.
238 DPKG_ADMINDIR
240 If set, it will be used as the dpkg data directory.
241 DPKG_COLORS
243 Sets the color mode (since dpkg 1.19.1). The currently accepted
244 values are: auto (default), always and never.
245
247 dh_installdeb(1).
2481.21.21 2023-02-25 dpkg-maintscript-helper(1)