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CentOS 7.0 - man page for dsync (centos section 1)

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DSYNC(1)				     Dovecot					 DSYNC(1)

       dsync - Dovecot's mailbox synchronization utility

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

       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)),  creat-
       ing  backups  of mails to a remote server, and convert mailboxes from/to different mailbox

       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 Dove-
       cot'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

       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.

       dsync recognizes the following command line options:

       -c config-file
	      read  configuration  from  the  given  config-file.   By default /etc/dovecot/dove-
	      cot.conf will be used.  -C alt_char Specifies an alternative mailbox  name  charac-
	      ter.   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 mail-

       -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 loca-

       -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.

	      The  first  mail	location  is based on configuration (mail_location or userdb set-
	      tings).  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

       dsync provides the following commands:

       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  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.

       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. Typi-
	   cally  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.

       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

       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.

	   o   Configuration uses mail_location = maildir:~/Maildir

	   o   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 ses-
	       sions (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.

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

       doveadm(1), doveadm-kick(1), doveconf(1), dovecot(1)

       Additional resources:

       dsync design

Dovecot v2.2				    2011-01-16					 DSYNC(1)

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