NAME¶
maildirsync - Online synchronizer for Maildir-format mailboxes
SYNOPSIS¶
maildirsync.pl [ --recursive ] [ --backup path ] [ --backup-tree ] \
[ --bzip2=bzip2 ] [ --gzip=gzip ] [ --maildirsync=maildirsync.pl ] \
[ --rsh=ssh ] [ --verbose ] [ --alg=md5 ] [ --delete-before ] \
[ --exclude=^/Folder1 ] [ --exclude=^/Fold.*er2 ] \
[ --exclude-source=^/Folder3 ] [ --exclude-target=^/Folder4 ] \
[ --rename="s/SourceFolder/TargetFolder/" ] \
[ --destination=win|lin ] \
[ -r ] [ -b path ] [ -B ] [ -R ssh ] [ -v ] [ -a ] [ -d ] \
source dest state_file.bz2
A simple two-way synchronization:
maildirsync.pl -rvv -a md5 desktop:Maildir Maildir lib/sync_desk_note.bz2
maildirsync.pl -rvv -a md5 Maildir desktop:Maildir lib/sync_note_desk.bz2
DESCRIPTION¶
maildirsync is a utility for online Maildir-synchronization. It is designed to
be used on live maildir folders, be fail-safe and optimized for minimal
bandwidth.
HOW IT WORKS¶
If you call the program once, it will propagate the changes from the source side
to the target side. Two-way synchronization requires two state-file and two
call for the program.
This propagation is basically two different operations from the source side:
- •
- New file is created or an existing file is moved to a new
location (e.g flags are changed).
- •
- A file is deleted in the source side. (Will be deleted in
the target side also).
At the first phase, the source side reads the state file (which stores the state
of the last synchronization) and compares it to the current state. It collects
the changes and sends them the target side.
The target side checks every file, which is marked new in the source file, and
decides if:
- •
- The file needs to be downloaded fully
- •
- Its header needs to be downloaded
- •
- We have this file already, so we need no data.
After it decides, it sends back the requests for new files.
Then the source side will send the files to the target side, which stores them
into the Maildir structure.
After the send operation is completed, both operation agrees upon the commit
operation. Then the source side saves the new state into the state file.
Note if we forget saving the state, or the program exits before it, the
operation can be restarted without data loss and inconsistency, because all
operations can be redone without errors.
REMOTE OPERATION¶
Maildir can be used in remote mode, so it can synchronize Maildir folders
between computers. If you want to use it this way, you have to provide the
host name before either the source or the target, like:
maildirsync.pl ... desktop:Maildir Maildir lib/maildirsync.bz2
or
maildirsync.pl ... Maildir desktop:Maildir lib/maildirsync.bz2
In remote mode, the target side must have maildirsync installed also. (See the
--maildirsync command-line argument).
The state-file must be in the same system as the source, so the source file in
the first example is searched in the "desktop" computer, and in the
local computer in the second example.
At least source or the destination must be local, so you cannot sync maildirs on
two different remote hosts.
COMMAND-LINE SWITCHES¶
Some command line switches has two form: a short form and a longer form. In the
short form, the switches can be grouped, like: -vvvr. Short options with
parameters also can be grouped, but the parameter must be the following
command-line argument, like:
maildirsync.pl -rvvvbR Maildir/Trash/cur ssh ...
It is the same as:
maildirsync.pl --recursive --verbose --verbose --verbose --backup \
Maildir/Trash/cur --rsh ssh ...
Long options can use '=' for assigning the parameter, or they can use the syntax
above.
Let's see what switches we have:
- --recursive, -r
- Process the base folder as the recursive collection of
Maildir folders.
- --backup dir, -b dir
- The deleted files are backed up to the specified directory
(this directory does not needs to be a maildir folder). The directory is
relative to the start-up directory, not the target base folder! The
directory is created if it does not exists.
- --backup-tree, -B
- This option is only useful when used in conjunction with
the --backup option. If set, deleted messages are moved to a Maildir
folders tree inside the backup directory with the same relative path. The
resulting backup directory can be used with any Maildir-capable
application (MUAs, MTAs, etc.).
- --bzip2 bzip2
- Path to the bzip2 utility (used only when the state file
has .bz2 extension). Note that using bzip2 is turned out to be quite
unstable, it sometimes leave the state file empty or corrupted.
- --gzip gzip
- Path to the gzip utility (used only when the state file has
.gz extension).
- --maildirsync maildirsync.pl
- Path to the maildirsync utility on the remote machine (if
we use maildirsync in remote mode).
- --rsh ssh
- Path to the utility, which can be used to connect to the
remote side. It defaults to "ssh". Note that the protocol, which
is used in remote mode, does not contain compression, but the data can be
compressed well, so I suggest using the ssh compression for this
purpose.
- --destination
- If it is provided, then it does transformation in the file
names. The transformations are the following:
- •
- win: Converts ":" to ":" (since
windows don't allow colon in the filename).
- •
- lin: Converts ":" to ":".
- --verbose, -v
- Adds more verbosity to the operation. There are currently 6
different verbosity level:
- 0
- No information at all.
- 1
- Main operations.
- 2
- Files sent, received, deleted, moved, md5
calculations.
- 3
- Directories read and created.
- 4
- Options + command echo.
- 5
- Misc info about file transfer.
- --alg md5, -a md5
- Selects the synchronization algorithm. Currently two
algorithms are provided:
- id (default)
- The messages are synchronized only by the ID of a message
(the ID can be determined by the message filename).
- md5
- This method is recommended for low bandwidth operations.
This mode can reduce the file transfers by checking the message moves on
the target side. This mode requires an MD5 sum on the body of the message,
so the first use of this mode can be quite time-consuming on both
sides.
For more information about the algorithms, read the chapter about that.
- --delete-before, -d
- Normally the delete operations on the target side is done
after the transfers. Use this switch if you don't have too much space on
your hard disk. Note that using this switch can reduce the chance of
detecting the message moves.
- --exclude, -x
- Excludes a directory regexp from the transfer and removes
it from the state file. This option can be used more than once to specify
more than one directories. Note, that the directory, which is matched
against these regexps are the relative path of the folders with a leading
'/', so if you want to exclude your Trash folder in the root of your
synchronization, then you have to use the following form:
--exclude=^/Trash
The excluded paths are used in either source or the target side also. So if
you exclude a very large directory, you will notice speedup in the source
and target side also.
Note that this regexp is matched for every directory that is read from the
filesystem, and every directory what is found in the state file. So if you
provide the exclude pattern as ^/Trash$, then it will skip the Trash
directory when traversing the directory structure, but it WON'T skip files
from the Trash/cur directory when reading from the state file! So be
careful if you use the exclude pattern with existing state file!
- --exclude-source, --exclude-target
- These parameters can be used to exclude files only from one
side of the synchronization. Can be useful with the rename options
(below).
- --rename
- Can be used to rename files when transferred from one side
to another. A perl expression is the parameter for this.
If you use this option, use it with care, because you have to provide
exactly the opposite of the name-transformation if you sync to the other
side, for example:
In one side, you can use (A to B):
--rename="s{^/Saved/}{/ToBeSaved/}" \
--exclude-target="^/Saved/" \
In the other side, you can use (B to A):
--exclude-source="^/Saved/" \
--rename="s{^/ToBeSaved/}{/Saved/}" \
In this case, the Saved folder in the A side will be synchronized with the
ToBeSaved folder in the B side, and the Saved folder in the B side will be
excluded from the synchronization. This scenario can be used when you
don't want to store your emails in the server, but you want to use the
"Saved" folder in the server too. In this case, the emails will
be downloaded from the server (A side) to your laptop (B side), then you
can move them to the Saved folder in B with a script. If this is done,
then you can resynchronize, then the saved files will disappear from the
server also.
ALGORITHMS¶
Currently the program has two algorithms, which can be used for synchronization.
- id (default)
- This algorithm is based on the message-id-s of the
messages. It assumes that a message-id exists only once in both
repositories with the same id. The id can be determined form the filename.
With this algorithm, you can trace the flag changes or the deletion of a
message and these changes can be propagated to the other side also. It
also handles if a message is copied from the "new" directory to
the "cur" directory without retransmit the files over the
network.
This algorithm is recommended if you want a simple and quite fast operation,
and if you have a not-so-slow internet connection.
- md5
- This algorithm does further calculations. It stores the
size of the header and the md5 sum of the message body for each message
besides the data that the "id" algorithm stores.
By using this algorithm, you can track the copies and moves of a message, so
you don't need to retransmit large files if you move them to a new folder.
If you copy or move a message from one folder to another, the header is
sometimes changed by the mail-reader program. This is why we cannot simply
calculate the MD5 sum of the whole message. A new message in a folder will
have a new identifier also, so it doesn't violate the law that a
message-id is unique.
When you copy or move a message from your INBOX to your "Save"
folder (for example), the new message is analyzed in the source side,
header-size and md5 sum is calculated on the new message, and from the
md5-hash, the source side can tell the target side what messages has the
same hash-value, so the target side can copy the body from the other
message. If the target side has successfully copied the body from one of
those provided messages, then only the header needs to be transmitted
across the network. If the target-side did not find the messages, then it
requests for the body also.
ONLINE OPERATION¶
Online operation means that the software can be used in an online mailbox also.
It assumes that the Maildir folder can be changed when the program is working,
so it tries to be as fail-safe as can be.
Every new file is opened in the "tmp" directory, and moved to the
target place only when the file is fully downloaded.
This mode of operation was the first priority, because this feature is missing
from most synchronizer software, including my "drsync" utility also.
SPEED¶
I am using this program to synchronize my Mailboxes. I have 9700 emails in my
mailbox and the state file (bzipped) is 283K.
The first time of a two-way synchronization between a P166 server and a
PIII/1200 notebook over a Cable network, where the starting position is an
already synchronized directory, tooks about 10 minutes. This time is used for
md5-calculation and message-id propagation.
The next two-way run tooks about 40 seconds.
These things are measured in Debian GNU/Linux testing/unstable operating system
(08 Oct 2002).
These are only the overhead of the software, not the real transfer. If you got a
very big email, it needs to be transferred at least one time on the network.
But if you have it in both sides, then it does not require any more transfer
if you save it to different folders.
TODO¶
I am currently happy with this feature set, but if I have time, I will implement
these features into the software. Anyway if you have time and willingness, I
accept patches also:
- •
- Message-size limit. By limiting the maximum transmitted
message, you can effectively use this software if you have very low
bandwidth.
- •
- Config-file and cron-safe operation.
COPYRIGHT¶
Copyright (c) 2000-2010 Szabo, Balazs (dLux)
All rights reserved. This program is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
AUTHOR¶
dLux (Szabo, Balazs) <dlux@dlux.hu>