Ubuntu Manpage: dsync - Dovecot's mailbox synchronization utility

Provided by: dovecot-core_2.2.9-1ubuntu2.6_amd64

NAME

       dsync - Dovecot's mailbox synchronization utility

SYNOPSIS

       dsync [options] mirror location2
       dsync [options] backup location2

DESCRIPTION

dsync is Dovecot's mailbox synchronization utility. It can be used for several different
use cases: Two-way synchronization of mailboxes in different servers (via ssh(1)),
creating backups of mails to a remote server, and convert mailboxes from/to different
mailbox formats.

The syncing is done as perfectly as possible: an IMAP or a POP3 client shouldn't be able
to notice any differences between the two mailboxes. Two-way syncing means that it's safe
to do any kind of modifications in both sides, and dsync will merge the changes without
losing any changes done on either side. This is possible because dsync can access
Dovecot's index logs that keep track of changes. It's of course possible to have conflicts
during merging, these are resolved in a safe way. See the dsync design document for more
information.

dsync uses the same configuration files as the rest of Dovecot (via doveconf binary). The
entire configuration can be changed by giving -c parameter to another configuration file,
or using -o parameter to override specific settings. When executing a remote dsync program
it works the same way: it uses its own local configuration.

dsync can be run completely standalone. It doesn't require any Dovecot server processes to
be running, except when using -u parameter to do a userdb lookup from auth process.

dsync can currently sync only one user at a time. If you want to dsync all users, you'll
need to get a list of all users and execute dsync separately for each one.

Any errors are written to stderr.

OPTIONS

dsync recognizes the following command line options:

-c config-file
read configuration from the given config-file. By default
/etc/dovecot/dovecot.conf will be used. -C alt_char Specifies an alternative
mailbox name character. If source and destination mailbox formats are different,
it's possible that on one side there exists a mailbox name that isn't valid for the
other side. These invalid mailbox names are fixed by replacing such invalid
characters with the given alt_char. The default is '_'.

-D Activates debug messages and makes dsync more verbose.

-f Makes dsync run in "full sync" mode rather than "fast sync" mode. In fast sync
mode dsync might skip syncing a mailbox, if both locations had modified it equally
many times (i.e. highest-modseqs were equal), but with different changes.

-m mailbox
Specifies the mailbox that should be synchronized or from which mails should be
converted. The default is to synchronize all respectively convert from all
mailboxes.

-o setting=value
Overrides the configuration setting from /etc/dovecot/dovecot.conf and from the
userdb with the given value. In order to override multiple settings, the -o option
may be specified multiple times.

-R Reverse backup direction, so mails in location2 are backed up to default mail
location.

-u user
Specifies that the userdb lookup for the given user should be done and used to set
up the environment (uid, gid, home, etc.). By default the system user's current
environment will be used.

-v Makes dsync more verbose.

ARGUMENTS

       location2
              The  first  mail  location  is  based  on  configuration  (mail_location  or userdb
              settings).     It's    also    possible    to     override     it     by     giving
              -o mail_location=mail_location  setting.   This  parameter  defines  the other mail
              location that is used.

              If the location is on local filesystem, you can use a regular  mail_location,  such
              as maildir:/backup/user/Maildir

              If  the  location  is  on  a  remote  server, dsync can ssh to it by giving host or
              user@host as the parameter.  If user is specified, it's given as  -u  parameter  to
              dsync, not to ssh.  The ssh username is always the default.

              The  final  way to specify a location is to give a full command line or a path to a
              script that executes the dsync.  For example:

              ssh mailuser@host dsync -u user

COMMANDS

       dsync provides the following commands:

   mirror
       Does a two-way synchronization between two mail locations.  Changes in both locations  are
       synchronized  to  the  other  one, without losing any changes made by either of them.  Any
       potential UID conflicts are resolved by giving them new UIDs.

   backup
       Backup mails from default mail location to location2 (or vice versa, if  -R  parameter  is
       given).  No changes are ever done to the source location.  Any changes done in destination
       are discarded.

EXIT STATUS

       dsync will exit with one of the following values:

       0   Synchronization was done perfectly.

       2   Synchronization was done without errors, but some changes couldn't  be  done,  so  the
           mailboxes  aren't  perfectly  synchronized.  Running  dsync  again usually fixes this.
           Typically this occurs for message modification sequences with newly created mailboxes.
           It can also occur if one of the mailboxes change during the syncing.

       1, >2
           Synchronization failed.

EXAMPLE

MIRRORING
Mirror mailboxes to a remote server. Any errors are written to stderr.

dsync -u username mirror username@example.com

If you need more complex parameters to ssh, you can use e.g.:

dsync -u username mirror ssh -i id_dsa.dovecot mailuser@example.com dsync -u username

CONVERTING
Assuming that the mail_location setting in /etc/dovecot/conf.d/10-mail.conf is set to:
mail_location = mdbox:~/mdbox, a logged in system user may convert her/his mails from its
Maildir in her/his home directory to the mdbox mailbox format. The user has to execute
the command:

dsync mirror maildir:~/Maildir

If you want to do this without any downtime, you can do the conversion one user at a time.
Initially:

• Configuration uses mail_location = maildir:~/Maildir

• Set up the possibility of doing per-user mail location using userdb extra fields.

Then for each user:

1. Run dsync mirror once to do the initial conversion.

2. Run dsync mirror again, because the initial conversion could have taken a while
and new changes could have occurred during it. This second time only applies
changes, so it should be fast.

3. Update mail extra field in userdb to mdbox:~/mdbox. If you're using auth cache,
you need to flush it.

4. Wait for a few seconds and then kill the user's all existing imap and pop3
sessions (that are still using maildir).

5. Run dsync mirror once more to apply final changes that were possibly done. After
this there should be no changes to Maildir, because the user's mail location has
been changed and all existing processes using it have been killed.

Once all users have been converted, you can set the default mail_location to mdbox and
remove the per-user mail locations from userdb.

REPORTING BUGS

       Report   bugs,   including   doveconf   -n   output,   to   the   Dovecot   Mailing   List
       <dovecot@dovecot.org>.     Information    about    reporting   bugs   is   available   at:
       http://dovecot.org/bugreport.html