When trying to deploy an app on the production server, the deploy:cleanup task always died for me like this:

  * executing `deploy:cleanup'
  * executing "ls -x /opt/sites/mysite/releases"
    servers: ["myserver"]
    [myserver] executing command
    command finished
 ** keeping 3 of 4 deployed releases
  * executing "rm -rf /opt/sites/mysite/releases/20080220092659"
    servers: ["myserver"]
    [myserver] executing command
 ** [out :: myserver] sudo: no passwd entry for app!
 ** [out :: myserver] 
    command finished
command "rm -rf /opt/sites/mysite/releases/20080220092659" failed on myserver

Turns out capistrano is for some reason trying to use a user called app in the cleanup task even though the :user parameter is set to something else in config/deploy.rb. The solution was to set the :runner parameter as well:

set :runner, 'someotheruser'

Don’t ask me why that worked. It seems a bit counterintuitive that the cleanup task uses the runner param rather than user. Found the hint towards the solution here.