MU INDEX(1)

NAME

mu-index - index e-mail messages stored in Maildirs

SYNOPSIS

mu [COMMON-OPTIONS] index

DESCRIPTION

mu index is the mu command for scanning the messages in Maildir directories and storing the results in a Xapian database. The data can then be queried using mu-find(1).

Before you can run mu index, you must initialize mu and its database with mu-init(1).

mu index understands Maildirs as defined by Daniel Bernstein for qmail(7). In addition, it understands recursive Maildirs (Maildirs within Maildirs), Maildir++. It also supports VFAT-based Maildirs which use "!" or ";" as the separators, instead of the standard ":".

E-mail messages are only considered for indexing if they reside in a directory named either cur or new. The special (as per the Maildir-specification) directory tmp is ignored, as are some cache directories for some other mail-clients. Other directories are scanned recursively.

Symbolic links are followed, and the directories can be spread over multiple filesystems; however, note that moving files around is much faster when they all reside on a single file-system. Be careful to avoid self-referential symlinks!

If there is a file called .noindex 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.

If there is a file called .noupdate in a directory, the contents of that directory and all of its subdirectories will be ignored. This can be useful to speed up things you have some maildirs that never change.

.noupdate does not affect already-indexed messages: you can still search for them. .noupdate is ignored when you start indexing with an empty database (such as directly after mu init).

There also the option --lazy-check which can greatly speed up indexing; see below for details.

A first run of mu index may take a few minutes if you have a lot of mail (tens or hundreds of thousands of messages). Fortunately, such a full scan needs to be done only rarely; after that, it suffices to index just the changes, which goes much faster. See PERFORMANCE (i,ii,iii) below for more information.

The optional cleanup-phase 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 -n, --nocleanup.

When mu index catches one of the signals SIGINT, SIGHUP or SIGTERM (e.g., when you press Ctrl-C during the indexing process), it attempts to shutdown gracefully: save and commit data and close the database etc. If it receives another signal (e.g., when pressing Ctrl-C once more), mu index will terminate immediately.

INDEX OPTIONS

  --lazy-check

In lazy-check mode, mu does not consider messages for which the time-stamp (ctime) of the directory in which they reside, has not changed since the previous time this directory was checked.

This is much faster than the non-lazy check, but won't update messages that have changed (rather than having been added or removed), since merely editing a message does not update the directory time-stamp. Of course, you can run mu-index occasionally without --lazy-check, to pick up such messages.

Furthermore, in lazy-check mode, files which have a ctime smaller than the time the previous indexing operation was completed, are ignored. This helps for the use-case where new messages can appear in big maildirs.

  --nocleanup

Disable the database cleanup that mu does by default after indexing.

  --reindex

Perform a complete reindexing of all the messages in the maildir.

  --muhome

Use a non-default directory to store and read the database, write the logs, etc. By default, mu uses the XDG Base Directory Specification (e.g. on GNU/Linux this defaults to ~/.cache/mu and ~/.config/mu). Earlier versions of mu defaulted to ~/.mu, which now requires --muhome=~/.mu.

The environment variable MUHOME can be used as an alternative to --muhome. The latter has precedence.

COMMON OPTIONS

  -d, --debug

Makes mu generate extra debug information, useful for debugging the program itself. Debug information goes to the standard logging location; see mu(1).

  -q, --quiet

Causes mu 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 mu index is much faster with --quiet, so it is recommended you use this option when using mu from scripts etc.

  --log-stderr

Causes mu to not output log messages to standard error, in addition to sending them to the standard logging location.

  --nocolor

Do not use ANSI colors. The environment variable NO_COLOR can be used as an alternative to --nocolor.

  -V, --version

Prints mu version and copyright information.

  -h, --help

Lists the various command line options.

ENCRYPTION

mu index does not decrypt messages, and only the metadata (such as headers) of encrypted messages makes it to the database. mu view and mu4e can decrypt messages, but those work with the message directly and the information is not added to the database.

PERFORMANCE

  indexing in ancient times (2009?)

As a non-scientific benchmark, a simple test on the author's machine (a Thinkpad X61s laptop using Linux 2.6.35 and an ext3 file system) with no existing database, and a maildir with 27273 messages:
    $ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
    $ time mu index --quiet
    66,65s user 6,05s system 27% cpu 4:24,20 total

(about 103 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
    0,48s user 0,76s system 10% cpu 11,796 total

(more than 56818 messages per second)

Note that each test flushes the caches first; a more common use case might be to run mu index when new mail has arrived; the cache may stay quite `warm' in that case:
    $ time mu index --quiet
    0,33s user 0,40s system 80% cpu 0,905 total

which is more than 30000 messages per second.

  indexing in 2012

As per June 2012, we did the same non-scientific benchmark, this time with an Intel i5-2500 CPU @ 3.30GHz, an ext4 file system and a maildir with 22589 messages. We start without an existing database.
    $ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
    $ time mu index --quiet
    27,79s user 2,17s system 48% cpu 1:01,47 total

(about 813 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
    0,13s user 0,30s system 19% cpu 2,162 total

(more than 173000 messages per second)

  indexing in 2016

As per July 2016, we did the same non-scientific benchmark, again with the Intel i5-2500 CPU @ 3.30GHz, an ext4 file system. This time, the maildir contains 72525 messages.
    $ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
    $ time mu index --quiet
    40,34s user 2,56s system 64% cpu 1:06,17 total

(about 1099 messages per second).

  indexing in 2022

A few years later and it is June 2022. There's a lot more happening during indexing, but indexing became multi-threaded and machines are faster; e.g. this is with an AMD Ryzen Threadripper 1950X (16 cores) @ 3.399GHz.

The instructions are a little different since we have a proper repeatable benchmark now. After building,
    $ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
    % THREAD_NUM=4 build/lib/tests/bench-indexer -m perf
    # random seed: R02Sf5c50e4851ec51adaf301e0e054bd52b
    1..1
    # Start of bench tests
    # Start of indexer tests
    indexed 5000 messages in 20 maildirs in 3763ms; 752 μs/message; 1328 messages/s (4 thread(s))
    ok 1 /bench/indexer/4-cores
    # End of indexer tests
    # End of bench tests

Things are again a little faster, even though the index does a lot more now (text-normalization, and pre-generating message-sexps). A faster machine helps, too!

  recent releases

Indexing the the same 93000-message mail corpus with the last few releases:
release | time (sec) | notes
1.4 | 160s |
1.6 | 178s |
1.8 | 97s |
1.10 | 120s | adds html indexing, sexp-caching
1.11 (master) | 96s | adds language-guessing, batch-size=50000

Quite some variation!

Over time new features / refactoring can change the timings quite a bit. At least for now, the latest code is both the fastest and the most feature-rich.

EXIT CODE

This command returns 0 upon successful completion, or a non-zero exit code otherwise.

0.  success

2.  no matches found. Try a different query

11. database schema mismatch. You need to re-initialize mu, see mu-init(1)

19. failed to acquire lock. Some other program has exclusive access to the mu database

99. caught an exception

REPORTING BUGS

Please report bugs at https://github.com/djcb/mu/issues.

AUTHOR

Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>

COPYRIGHT

This manpage is part of mu 1.12.12.

Copyright © 2008-2025 Dirk-Jan C. Binnema. License GPLv3+: GNU GPL version 3 or later https://gnu.org/licenses/gpl.html. This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

maildir(5), mu(1), mu-init(1), mu-find(1), mu-cfind(1)