maildirsync - Online synchronizer for Maildir-format mailboxes
maildirsync [ --recursive ] [ --backup path ] [ --bzip2=bzip2 ] \
[ --gzip=gzip ] [ --maildirsync=maildirsync ] [ --rsh=ssh ] \
[ --verbose ] [ --alg=md5 ] [ --delete-before ] \
[ --exclude=^/Folder1 ] [ --exclude=^/Fold.*er2 ] \
[ --exclude-source=^/Folder3 ] [ --exclude-target=^/Folder4 ] \
[ --rename="s/SourceFolder/TargetFolder/" ] \
[ -r ] [ -b path ] [ -R ssh ] [ -v ] [ -a ] [ -d ] \
source dest state_file.bz2
A simple two-way synchronization:
maildirsync -rvv -a md5 desktop:Maildir Maildir lib/sync_desk_note.bz2
maildirsync -rvv -a md5 Maildir desktop:Maildir lib/sync_note_desk.bz2
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 tow different operation from the source
· 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
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.
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 ... desktop:Maildir Maildir lib/maildirsync.bz2
maildirsync ... 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.
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 -rvvvbR Maildir/Trash/cur ssh ...
It is the same as:
maildirsync --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:
Process the base folder as the recursive collection of Maildir
--backup dir, -b dir
The deleted files are backed up to the sepcified 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.
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.
Path to the gzip utility (used only when the state file has .gz
Path to the maildirsync utility on the remote machine (if we use
maildirsync in remote mode).
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
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 Direcotries read and created.
4 Options + command echo.
5 Misc info about file transfer.
--alg md5, -a md5
Selects the synchronization algorithm. Currently two alrogithm is
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
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.
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
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!
These parameters can be used to exclude files only from one side of
the synchronization. Can be useful with the rename options (below).
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):
In the other side, you can use (B to A):
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.
Currently the porgram has two algorithms, which can be used for
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
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 is 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 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
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.
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
· Config-file and cron-safe operation.
Copyright (c) 2000-2002 Szab\[’o], Bal\[’a]zs (dLux)
All rights reserved. This program is free software; you can
redistribute it and/or modify it under the same terms as Perl itself.
dLux (Szab\[’o], Bal\[’a]zs) <firstname.lastname@example.org>