Onde o Aptitude registra seus avisos?

Não há nenhum - o aptitude não grava erros ou avisos no disco por padrão. Tudo o que acontece /var/log/aptitudesão instalações.

Se você quiser registro extra, você precisa informar aptitudeisso.

De man aptitude:

   --log-file=<file>
       If <file> is a nonempty string, log messages will be written to it, except that if
       <file> is “-”, the messages will be written to standard output instead. If this option
       appears multiple times, the last occurrence is the one that will take effect.

       This does not affect the log of installations that aptitude has performed
       (/var/log/aptitude); the log messages written using this configuration include
       internal program events, errors, and debugging messages. See the command-line option
       --log-level to get more control over what gets logged.

       This corresponds to the configuration option Aptitude::Logging::File.

   --log-level=<level>, --log-level=<category>:<level>
       --log-level=<level> causes aptitude to only log messages whose level is <level> or
       higher. For instance, setting the log level to error will cause only messages at the
       log levels error and fatal to be displayed; all others will be hidden. Valid log
       levels (in descending order) are off, fatal, error, warn, info, debug, and trace. The
       default log level is warn.

       --log-level=<category>:<level> causes messages in <category> to only be logged if
       their level is <level> or higher.

       --log-level may appear multiple times on the command line; the most specific setting
       is the one that takes effect, so if you pass --log-level=aptitude.resolver:fatal and
       --log-level=aptitude.resolver.hints.match:trace, then messages in
       aptitude.resolver.hints.parse will only be printed if their level is fatal, but all
       messages in aptitude.resolver.hints.match will be printed. If you set the level of the
       same category two or more times, the last setting is the one that will take effect.

       This does not affect the log of installations that aptitude has performed
       (/var/log/aptitude); the log messages written using this configuration include
       internal program events, errors, and debugging messages. See the command-line option
       --log-file to change where log messages go.

       This corresponds to the configuration group Aptitude::Logging::Levels.

[editar] OK... tentar levar você até a água e fazer você beber está demorando muito:

Basta criar o arquivo /etc/apt/apt.conf.d/50aptitudecom o seguinte conteúdo - o que também evitará que você precise usar opções de linha de comando:

Aptitude::Logging::File "/var/log/aptitude.out";
Aptitude::Logging::Levels "*:info";

Aqui está o que funcionou para mim:

Sempre que eu ligo Aptitude , eu uso

aptitude --log-file=/tmp/AptitudeLog.log --log-level=info

Então, como nunca me lembrarei de onde procurar se precisar de alguma informação de log associada, deixei links para o arquivo de log temporário acima /var/loge/var/log/apt

Fim do problema!