Chapter 6. Package maintainer scripts and installation procedure

43

old postrm

upgrade

new version

2 If this fails,

dpkg

will attempt:

new postrm

failed upgrade

old version

Error unwind, for both cases:

old preinst

abort upgrade

new version

This is the point of no return   if

dpkg

gets this far, it won't back off past this point

if an error occurs. This will leave the package in a fairly bad state, which will require

a successful re installation to clear up, but it's when

dpkg

starts doing things that are

irreversible.

6 Any files which were in the old version of the package but not in the new are removed.

7 The new file list replaces the old.

8 The new maintainer scripts replace the old.

9 Any packages all of whose files have been overwritten during the installation, and which

aren't required for dependencies, are considered to have been removed. For each such

package

1

dpkg

calls:

disappearer's postrm

disappear \

overwriter overwriter version

2 The package's maintainer scripts are removed.

3 It is noted in the status database as being in a sane state, namely not installed (any

conffiles it may have are ignored, rather than being removed by

dpkg

). Note that

disappearing packages do not have their prerm called, because

dpkg

doesn't know

in advance that the package is going to vanish.

10 Any files in the package we're unpacking that are also listed in the file lists of other pack 

ages are removed from those lists. (This will lobotomize the file list of the  conflicting 

package if there is one.)

11 The backup files made during installation, above, are deleted.

12 The new package's status is now sane, and recorded as  unpacked .

Here is another point of no return   if the conflicting package's removal fails we do not

unwind the rest of the installation; the conflicting package is left in a half removed limbo.

13 If there was a conflicting package we go and do the removal actions (described below),

starting with the removal of the conflicting package's files (any that are also in the pack 

age being installed have already been removed from the conflicting package's file list,

and so do not get removed now).