<title>Deleting Content From Fossil</title>

<h2>Good Reasons for Removing Content from a Fossil Repository</h2>

Fossil is designed to keep all historical content forever. Fossil
purposely makes it difficult for users to delete content.  Old content
is part of the project's <i>*ahem*</i> fossil record and should be
maintained indefinitely to maintain an accurate history of the project.

Nevertheless, there may occasionally arise legitimate reasons for
deleting content.  Such reasons include:

  *  Spammers inserted inappropriate content into a wiki page, forum post,
     or ticket. Fossil lets you easily hide or amend such content, but
     since it is not a legitimate part of the project's history, there
     is no value in keeping it, so it is best removed permanently.

  *  A file that contains trade secrets or that is under someone else's
     copyright was accidentally committed and needs to be backed out.

  *  A malformed control artifact was inserted and is disrupting the
     operation of Fossil.

  *  A legitimate legal request was received requiring content to
     be removed. This would most likely be related to the accidental 
     intellectual property error or spam cases listed above. Some countries 
     recognise software patents, and so allow legal claims targetting code 
     commits. Some countries can require publicly-available encryption 
     software to be taken down if it is committed to the DAG without 
     the correct government authorisation.

<h2>Alternatives</h2>

All of these are rare cases: Fossil is [./antibot.wiki | designed to
foil spammers up front], legally problematic check-ins should range from
rare to nonexistent, and you have to go way out of your way to force
Fossil to insert bad control artifacts. Therefore, before we get to
methods of permanently deleting content from a Fossil repos, let's give
some alternatives that usually suffice, which don't damage the project's
fossil record:

  *  When a forum post or wiki article is "deleted," what actually
     happens is that a new empty version is added to the Fossil repository.
     The web interface interprets this
     as "deleted," but the prior version remains available if you go
     digging for it.
 
  *  When you close a ticket, it's marked in a way that causes it
     to not show up in the normal ticket reports. You usually want to
     give it a Resolution such as "Rejected" when this happens, plus
     possibly a comment explaining why you're closing it. This is all new
     information added to the ticket, not deletion.
 
  *  When you <tt>fossil rm</tt> a file, a new manifest is
     checked into the repository with the same file list as for the prior
     version minus the "removed" file. The file is still present in the
     repository; it just isn't part of that version forward on that
     branch.
 
  *  If you make a bad check-in, you can shunt it off to the side
     by amending it to put it on a different branch, then continuing
     development on the prior branch:
     <br><br>
     <code>$ fossil amend abcd1234 --branch BOGUS --hide<br>
     $ fossil up trunk</code>
     <br><br>
     The first command moves check-in ID <tt>abcd1234</tt> (and any
     subsequent check-ins on that branch!) to a branch called
     <tt>BOGUS</tt>, then hides it so it doesn't show up on the
     timeline. You can call this branch anything you like, and you can
     re-use the same name as many times as you like. No content is
     actually deleted: it's just shunted off to the side and hidden away.
     You might find it easier to do this from the Fossil web UI in
     the "edit" function for a check-in.
     <br><br>
     The second command returns to the last good check-in on that branch
     so you can continue work from that point.
 
  *  When the check-in you want to remove is followed by good
     check-ins on the same branch, you can't use the previous method,
     because it will move the good check-ins, too. The solution is:
     <br><br>
     <tt>$ fossil merge --backout abcd1234</tt>
     <br><br>
     That creates a diff in the check-out directory that backs out the
     bad check-in <tt>abcd1234</tt>. You then fix up any merge conflicts,
     build, test, etc., then check the reverting change into the
     repository. Again, nothing is actually deleted; you're just adding
     more information to the repository which corrects a prior
     check-in.

<h2>Exception: Non-versioned Content</h2>

It is normal and expected to delete data which is not versioned, such as
usernames and passwords in the user table. The [/help/scrub|fossil scrub]
command will remove all sensitive non-versioned data from a repository.

The scrub command will remove user 'bertina', along with their password,
any supplied IP address, any concealed email address etc. However, in the 
DAG, commits by 'bertina' will continue to be visible unchanged even though
there is no longer any such user in Fossil.

<h2>Shunning</h2>

Fossil provides a mechanism called "shunning" for removing content from
a repository.

Every Fossil repository maintains a list of the hash names of
"shunned" artifacts.
Fossil will refuse to push or pull any shunned artifact.
Furthermore, all shunned artifacts (but not the shunning list
itself) are removed from the
repository whenever the repository is reconstructed using the
"rebuild" command.

<h3>Shunning lists are local state</h3>

The shunning list is part of the local state of a Fossil repository.
In other words, shunning does not propagate to a remote repository
using the normal "sync" mechanism.  An artifact can be
shunned from one repository but be allowed to exist in another.  The fact that
the shunning list does not propagate is a security feature.  If the
shunning list propagated then a malicious user (or
a bug in the fossil code) might introduce a shun record that would
propagate through all repositories in a network and permanently
destroy vital information.  By refusing to propagate the shunning list,
Fossil ensures that no remote user will ever be able to remove
information from your personal repositories without your permission.

The shunning list does not propagate to a remote repository
by the normal "sync" mechanism,
but it is still possible to copy shuns from one repository to another
using the "configuration" command:

    <b>fossil configuration pull shun</b> <i>remote-url</i><br>
    <b>fossil configuration push shun</b> <i>remote-url</i>

The two command above will pull or push shunning lists from or to
the <i>remote-url</i> indicated and merge the lists on the receiving
end.  "Admin" privilege on the remote server is required in order to
push a shun list.  In contrast, the shunning list will be automatically
received by default as part of a normal client "pull" operation unless
disabled by the "<tt>auto-shun</tt>" setting.

Note that the shunning list remains in the repository even after the
shunned artifact has been removed.  This is to prevent the artifact
from being reintroduced into the repository the next time it syncs with
another repository that has not shunned the artifact.

<h3>Managing the shunning list</h3>

The complete shunning list for a repository can be viewed by a user
with "admin" privilege on the "/shun" URL of the web interface to Fossil.
That URL is accessible under the "Admin" button on the default menu
bar.  Items can be added to or removed from the shunning list.  "Sync"
operations are inhibited as soon as the artifact is added to the
shunning list, but the content of the artifact is not actually removed
from the repository until the next time the repository is rebuilt.

When viewing individual artifacts with the web interface, "admin"
users will usually see a "Shun" option in the submenu that will take
them directly to the shunning page and enable that artifact to be
shunned with a single additional mouse click.
