Chapter 6. Package maintainer scripts and installation procedure

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  new postrm

abort install

  new postrm

abort install

old version

  new postrm

abort upgrade

old version

  disappearer's postrm

disappear

overwriter overwriter version

6.5 Details of unpack phase of installation or upgrade

The procedure on installation/upgrade/overwrite/disappear (i.e., when running

dpkg

  unpack

, or the unpack stage of

dpkg   install

) is as follows. In each case, if a ma 

jor error occurs (unless listed below) the actions are, in general, run backwards   this means

that the maintainer scripts are run with different arguments in reverse order. These are the

 error unwind  calls listed below.

1

1 If a version of the package is already installed, call

old prerm

upgrade

new version

2 If the script runs but exits with a non zero exit status,

dpkg

will attempt:

new prerm

failed upgrade

old version

Error unwind, for both the above cases:

old postinst

abort upgrade

new version

2 If a  conflicting  package is being removed at the same time:

1 If any packages depended on that conflicting package and

  auto deconfigure

is specified, call, for each such package:

deconfigured's prerm

deconfigure \

in favour

package being installed version

\

removing

conflicting package version

Error unwind:

deconfigured's postinst

abort deconfigure \

in favour

package being installed but failed version

\

removing

conflicting package version

The deconfigured packages are marked as requiring configuration, so that if

  install

is used they will be configured again if possible.

2 To prepare for removal of the conflicting package, call:

conflictor's prerm

remove \

in favour

package new version

Error unwind:

conflictor's postinst

abort remove \

in favour

package new version