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.TH MU 1 "February 2010" "User Manuals"
mu \- index and search e-mail messages stored in Maildirs
.B mu index [options]
.B mu cleanup [options]
.B mu find [options] <search expression>
.B mu view <file> [<files>]
.B mu mkdir [options] <dir> [<dirs>]
.B mu [options]
\fBmu\fR is a set of tools for dealing with e-mail messages in Maildirs.
Its main function is enable searching of e-mail messages. It does so by
scanning a Maildir directory tree and analyzing the e-mail messages found. The
results of this analysis are stored in a database, which can then be queried.
In addition to indexing and searching, \fBmu\fR also offers functionality for
viewing messages and creating maildirs.
\fBmu\fR can be used from the command line, or can be integrated with e-mail
clients. This manpage contains examples of both.
\fBmu\fR offers the following commands:
for indexing (analyzing) the contents of your Maildirs, and storing the
information in a database
for removing messages from the database for which there is no longer a
corresponding message file in the file system
for finding messages in your database, using certain search parameters (see
below for details)
for displaying e-mail messages
for creating Maildirs
The various commands are discussed in more detail below
\fBmu\fR offers a number of general options that apply to all commands:
\fB\-a\fR, \fB\-\-muhome\fR
causes \fBmu\fR to use an alternative directory to
store and read its database and logs. By default, \fI~/.mu\fR is used.
\fB\-d\fR, \fB\-\-debug\fR
makes \fBmu\fR generate extra debug information,
useful for debugging the program itself. By default, debug information goes to
the log file, \fI~/.mu/mu.log\fR. It can safely be deleted when \fBmu\fR is
not running. Note, with the debug option, the log file can grow rather
quickly. See the note on logging below.
\fB\-q\fR, \fB\-\-quiet\fR
causes \fBmu\fR not to output informational
messages and progress information to standard output, but only to the log
file. Error messages will still be sent to standard error. Note that \fBmu
index\fR is \fBmuch\fR faster with \fB\-\-quiet\fR, so it is recommended you
use this option when using \fBmu\fR from scripts etc.
\fB\-e\fR, \fB\-\-log-stderr\fR
causes \fBmu\fR not to output all log messages
to standard error, in addition to sending them to the log file.
\fB\-v\fR, \fB\-\-version\fR
outputs the \fBmu\fR-version and copyright
\fB\-h\fR, \fB\-\-help\fR
list the various command line options, while
\fB\-\-help\-index\fR, \fB\-\-help\-find\fR and \fB\-\-help\-all\fR list only
the options for one command, or all of the commands.
Using the
.B index
command, you can index your Maildir directories, and store the information in
a Xapian database.
.B index
understands Maildirs as defined by Dan Bernstein for qmail(7). In addition, it
understands recursive Maildirs (Maildirs within Maildirs), Maildir++. It can
also deal with VFAT-based Maildirs which use '!' as the seperators instead
of ':' as used by Tinymail/Modest and some other e-mail programs.
E-mail messages which are not stored in something resembling a maildir leaf
directory (\fIcur\fR and \fInew\fR) are ignored.
Currently, symlinks are not followed.
If there is a file called \fI.noindex\fR in a directory, the contents of that
directory and all of its subdirectories will be ignored. This can be useful to
exclude certain directories from the indexing process, for example directories
with spam-messages.
The first run of \fBmu index\fR may take a few minutes if you have a lot of
mail (ten thousands of messages). Fortunately, such a full scan needs to be
done only once, after that it suffices to index the changes, which goes much
faster. Also note that a substantial amount of the time goes to printing the
progress information; if you turn that off (with \fB\-q\fR or
\fB\-\-quiet\fR), it goes a lot faster. See the 'Note on performance' below
for more information.
The optional phase two of the indexing-process is the removal of messages from
the database for which there is no longer a corresponding file in the
Maildir. If you do not want this, you can use \fB\-n\fR, \fB\-\-nocleanup\fR.
When \fBmu index\fR catches on of the signals \fBSIGINT\fR, \fBSIGHUP\fR or
\fBSIGTERM\fR (e.g,, when you press Ctrl-C during the indexing process), it
tries to shutdown gracefully; it tries to save and commit data, and close the
database etc. If it receives another signal (e.g,, when pressing Ctrl-C once
more), \fBmu index\fR will terminate immediately.
.SS Indexing options
\fB\-m\fR, \fB\-\-maildir\fR=\fI<maildir>\fR
starts searching at \fI<maildir>\fR. By default, \fBmu\fR uses whatever the
\fBMAILDIR\fR environment variable is set to; if that is not set, it tries
\fI~/Maildir\fR \. In either case, the path must be \fBabsolute\fR.
\fB\-r\fR, \fB\-\-reindex\fR
re-index all mails, even ones that are already in the database.
\fB\-n\fR, \fB\-\-nocleanup\fR
disables the database cleanup that \fBmu\fR does by default after indexing.
\fB\-y\fR, \fB\-\-rebuild\fR
clear all messages from the database before
indexing. This is effectively the same as removing the database. The
difference with \fB\-\-reindex\fR is that \fB\-\-rebuild\fR guarantees that
after the indexing has finished, there are no 'old' messages in the database
anymore, which is not true with \fB\-\-reindex\fR when indexing only a part of
messages (using \fB\-\-maildir\fR). For this reason, it is necessary to run
\fBmu index \-\-rebuild\fR when there is an upgrade in the database
format. \fBmu index\fR will issue a warning about this.
\fB\-u\fR, \fB\-\-autoupgrade\fR automatically use \fB\-y\fR, \fB\-\-empty\fR
when \fBmu\fR notices that the database version is not up-to-date. This option
is for use in cron scripts and the like, so they won't require any user
interaction, even when mu introduces a new database vesion.
It is probably not a good idea to run multiple instances of
.B mu index
concurrently. No data loss should occur, but one or more of the instances may
experience errors due to database locks.
Also note that, before indexing is completed, searches for messages may fail,
even if they have already been indexed, as some of the esssential database
information will only be written in batches during the indexing process.
.SS A note on performance
As a non-scientific benchmark, a simple test on the authors machine (a
Thinkpad X61s laptop using Linux 2.6.31 and an ext3 file system) with no
existing database, and a maildir with 14,200 messages:
$ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
$ time mu index --quiet
83.36s user 6.49s system 43% cpu 3:26.21 total
(about 69 messages per second)
A second run, which is the more typical use case when there is a database
already, goes much faster:
$ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
$ time mu index --quiet
0.29s user 0.62s system 14% cpu 6.409 total
(about 2219 message per second)
Note that each of test flushes the caches first; a more common use case might
be to run \fBmu index\fR when new mail has arrived; the cache may stay
quite 'warm' in that case:
$ time mu index --quiet
0.19s user 0.21s system 98% cpu 0.402 total
which is more than 35,0000 messages per second (there is some variance here,
but the author has not seen it getting under 30,0000 messages per second).
The \fBcleanup\fR command removes messages for which no corresponding file can
be found, from the database. Note that this is done automatically when running
\fBmu index\fR (unless \fB\-\-nocleanup\fR was specified).
The \fBfind\fR command starts a search for messages in the database that match
the search pattern.
The search pattern is taken as a command line parameter. If the search
parameter consists of multiple parts (multiple command line parameters) they
are treated as if there were a logical \fBAND\fR between them.
If you want to make your own constructions (using \fBAND\fR, \fBOR\fR,
\fBNOT\fR etc., you have to put quote them so \fBmu\fR can consider them as a
\fBmu\fR relies on the Xapian database for its searching capabilities, so it
offers all the search functionality that Xapian offers; please refer to:
All queries are logged in \fI<mu-home>/mu.log\fR.
The basic way to search a message is to type some words matching it, as you
would do in a search engine on the internet, ie.
mu find monkey banana
will find all message that have both 'monkey' and 'banana'. Matching is
case-insensitive and somewhat intelligent, in that it tries to recognize
various forms of a word (such as plulars); this is all courtesy of Xapina.
\fBmu\fR also recognizes prefixes for specific fields in a messages; for
mu find subject:penguin
to find messages with have the word \fBpenguin\fR in the subject field. You
can abbreviate \fBsubject:\fR to just \fBs:\fR. Here is the full table of the
search fields and their abbreviations:
cc,c CC (Carbon-Copy) recipient
from,f Message sender
subject,s Message subject
to,t To: recipient
maildir,m Maildir
msgid,i Message-ID
The Maildir field describes the directory path starting \fBafter\fR the
Maildir-base path, and before the \fI/cur/\fR or \fI/new/\fR part. So for
example, if there's a message with the file name
\fI~/Maildir/lists/running/cur/1234.213:2,\fR, you could find it (and all the
other messages in the same maildir) with:
mu find maildir:lists/running
.SS Find options
The \fBfind\fR-command has various options that influence the way \fBmu\fR
displays the results. If you don't specify anything, the defaults are
\fI\-\-fields="d f s"\fR, \fI\-\-sortfield=date\fR and \fI\-\-descending\fR.
\fB\-f\fR, \fB\-\-fields\fR=\fI<fields>\fR
specifies a string that determines which fields are shown in the output. This
string consists of a number of characters (such as 's' for subject or 'f' for
from), which will replace with the actual field in the output. Fields that are
not known will be output as-is, allowing for some simple formatting.
For example:
mu find subject:snow --fields "d f s"
would list the date, subject and sender of all messages with 'snow' in the
their subject.
The table of replacement characters is superset of the list mentions for
search parameters:
t \fBt\fRo: recipient
c \fBc\fRc: (Carbon-Copy) recipient
d Sent \fBd\fRate of the message
f Message sender (\fBf\fRrom:)
g Message flags (fla\fBg\fRs)
l Full path to the message (\fBl\fRocation)
p Message \fBp\fRriority (high, normal, low)
s Message \fBs\fRubject
i Message-\fBi\fRd
m \fBm\fRaildir
The message-flags output is a string, consisting of zero or more of the
following characters.
D Draft Message
F Flagged
N New message (in new/ Maildir)
P Passed ('Handled')
R Replied
S Seen
T Marked for deletion
a Has attachment
s Signed message
x Encrypted message
Note that these are theoretical flags, which may or may not be actually in
\fB\-s\fR, \fB\-\-sortfield\fR \fR=\fI<field>\fR and \fB\-z\fR, \fB\-\-descending\fR
specifies the field to sort the search results by, and the direction. The
following fields are supported:
cc,c CC (Carbon-Copy) recipient
date,d message sent date
from,f message sender
maildir,m maildir
msgid,i message id
prio,p message priority
subject,s message subject
to,t To:-recipient
Thus, for example, to sort messages by date, you could specify:
$ mu find fahrrad --fields "d f s" --sortfield=date --descending
Note, if you specify a sortfield, by default, they are sorted in descending
order (e.g., from lowest to highest). This is usually a good choice, but for
dates it may be more useful to sort in the opposite direction.
\fB\-x\fR, \fB\-\-xquery\fR
shows the Xapian query corresponding to your search terms. This is mostly
useful for debugging.
\fB\-l\fR, \fB\-\-linksdir\fR \fR=\fI<dir>\fR and \fB\-c\fR, \fB\-\-clearlinks\fR
output the results as a maildir with symbolic links to the found
messages. This enables easy integration with mail-clients (see below for more
information). \fBmu\fR will create the maildir if it does not exist yet.
If you specify \fB\-\-clearlinks\fR, all existing symlinks will be cleared
from the target maildir; this allows for re-use of the same directory. An
alternative would be to delete the target directory before, but this has a big
chance of accidentaly removing something that should not be removed.
$ mu find grolsch --linksdir=~/Maildir/search --clearlinks
will store links to found messages in \fI~/Maildir/search\fR. If the directory
does not exist yet, it will be created.
Note: when \fBmu\fR creates a Maildir for these links, it automatically
inserts a \fI.noindex\fR file, to exclude the directory from \fBmu
.SS Example queries
Here are some simple examples of \fBmu\fR search queries; you can make many
more complicated queries using various logical operators, parentheses and so
on, but in the author's experience, it's usually faster to find a message with
a simple query just searching for some words.
Find all messages with both 'bee' and 'bird' (in any field)
$ mu find 'bee AND bird'
or shorter, because \fBAND\fR is implied:
$ mu find bee bird
Find all messages with either Frodo or Sam:
$ mu find 'Frodo OR Sam'
Find all messages with the 'wombat' as subject, and 'capibara' anywhere:
$ mu find subject:wombat capibara
Find all messages in the 'Archive' folder from Fred:
$ mu find from:fred maildir:Archive
.SS Integrating mu find with mail clients
For \fBmutt\fR you can use the following in your \fImuttrc\fR; pressing the F8
key will start a search, and F9 will take you to the results.
# mutt macros for mu
macro index <F8> "<shell-escape>mu find -c -l ~/Maildir/search " \
"mu find"
macro index <F9> "<change-folder-readonly>~/Maildir/search" \
"display mu find results"
If you use Wanderlust for \fBemacs\fR, the following definitons can be used;
typing 'Q' will start a query.
;; mu integration for Wanderlust
(defvar mu-wl-mu-program "mu")
(defvar mu-wl-search-folder "search")
(defun mu-wl-search ()
"search for messages with `mu', and jump to the results"
(let* ((muexpr (read-string "Find messages matching: "))
(sfldr (concat elmo-maildir-folder-path "/"
(cmdline (concat mu-wl-mu-program " find "
"--clearlinks --linksdir='" sfldr "' "
(= 0 (shell-command cmdline))))
(defun mu-wl-search-and-goto ()
"search and jump to the folder with the results"
(if (mu-wl-search)
(concat "." mu-wl-search-folder)
'force-update nil nil t)
(message "Query failed")))
With the \fBview\fR command, you can view one or more e-mail messages as they
are stored as files on disk. It does not require or use the Xapian database.
Currently, the command shows some common headers (From:, To:, Cc:, Subject:
and Date:) and the plain-text body of the message.
With the \fBmkdir\fR command, you can create new Maildirs with permissions
0755. For example,
mu mkdir tom dick harry
will create three Maildirs \fItom\fR, \fIdick\fR and \fIharry\fR.
If the creation somehow fails, for safety reasons, \fBno\fR attempt is made to
remove any parts that were created.
By default, \fBmu index\fR stores its message database in \fI~/.mu/xapian\fR;
the database has an embedded version number, and \fBmu\fR will automatically
update it when it notices a different version. This allows for automatic
updating of \fBmu\fR-versions, without the need to clear out any old
However, note that versions of \fBmu\fR before 0.7 used a different scheme,
which put the database in \fI~/.mu/xapian\-<version>\fR. These older databases
can safely be deleted. Starting from version 0.7, this manual cleanup should
no longer be needed.
By default, \fBmu\fR stores logs of its operations and queries in \fI~/.mu/mu.log\fR.
Upon startup, \fBmu\fR checks the size of this log file. If it exceeds 1 MB,
it will be moved to \fI~/.mu/mu.log.old\fR, overwriting any existing file of
that name, and start with an empty \fI~/.mu/mu.log\fR. This scheme allows for
continued use of \fBmu\fR without the need for any manual maintenance of log
To store these files elsewhere from their default location, one can use the
\fI\-\-muhome\fR option, as discussed in the \fBGENERAL OPTIONS\fR section.
As mentioned, \fBmu index\fR uses \fBMAILDIR\fR to find the user's Maildir if
it has not been specified explicitly \fB\-\-maildir\fR=\fI<maildir>\fR. If
MAILDIR is not set, \fBmu index\fR will try \fI~/Maildir\fR.
There probably are some; please report bugs when you find them:
Dirk-Jan C. Binnema <>
.BR maildir(5)
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