Introduction to CrackLib

The CrackLib package contains a library used to enforce strong passwords by comparing user selected passwords to words in chosen word lists.

Package Information

Additional Downloads

There are additional word lists available for download, e.g., from CrackLib can utilize as many, or as few word lists you choose to install.



Users tend to base their passwords on regular words of the spoken language, and crackers know that. CrackLib is intended to filter out such bad passwords at the source using a dictionary created from word lists. To accomplish this, the word list(s) for use with CrackLib must be an exhaustive list of words and word-based keystroke combinations likely to be chosen by users of the system as (guessable) passwords.

The default word list recommended above for downloading mostly satisfies this role in English-speaking countries. In other situations, it may be necessary to download (or even create) additional word lists.

Note that word lists suitable for spell-checking are not usable as CrackLib word lists in countries with non-Latin based alphabets, because of “word-based keystroke combinations” that make bad passwords.

Installation of CrackLib

If desired, apply the Heimdal patch (note that with this patch the original library is not affected; this patch only creates an additional library used by the Heimdal password-checking routines):

patch -Np1 -i ../cracklib-2.8.3-heimdal-1.patch

Install CrackLib by running the following commands:

./configure --prefix=/usr --datadir=/lib &&

Now, as the root user:

make install &&
mv -v /usr/lib/* /lib &&
ln -v -sf ../../lib/ /usr/lib/

The following commands can be used to install the recommended word list. Other word lists (text based, one word per line) can also be used by simply installing them into /usr/share/dict.

install -v -m644 -D ../cracklib-words.gz \
    /usr/share/dict/cracklib-words.gz &&
gunzip -v /usr/share/dict/cracklib-words.gz &&
ln -v -s cracklib-words /usr/share/dict/words &&
echo $(hostname) >>/usr/share/dict/cracklib-extra-words &&
create-cracklib-dict /usr/share/dict/cracklib-words \

If desired, check the proper operation of the library as an unprivileged user using the tests included with the package:

make test

Command Explanations

--datadir=/lib: This parameter forces the installation of the CrackLib dictionary to the /lib hierarchy.

mv -v /usr/lib/* /lib and ln -v -sf ../../lib/ ...: These two commands move the library and associated symlink from /usr/lib to /lib, then recreates the /usr/lib/ symlink pointing to the relocated file.

install -v -m644 -D ...: This command creates the /usr/share/dict directory (if it doesn't already exist) and installs the compressed word list there.

ln -v -s cracklib-words /usr/share/dict/words: The word list is linked to /usr/share/dict/words as historically, words is the primary word list in the /usr/share/dict directory. Omit this command if you already have a /usr/share/dict/words file installed on your system.

echo $(hostname) >>...: The value of hostname is echoed to a file called cracklib-extra-words. This extra file is intended to be a site specific list which includes easy to guess passwords such as company or department names, user's names, product names, computer names, domain names, etc.

create-cracklib-dict ...: This command creates the CrackLib dictionary from the word lists. Modify the command to add any additional word lists you have installed.


Installed Programs: cracklib-check, cracklib-format, cracklib-packer, cracklib-unpacker and create-cracklib-dict
Installed Libraries: libcrack.[so,a] and optionally, libcrack_heimdal.[so,a]
Installed Directories: /lib/cracklib and /usr/share/dict

Short Descriptions


is used to create the CrackLib dictionary from the given word list(s).


provides a fast dictionary lookup method for strong password enforcement.

Last updated on 2005-08-14 15:03:38 -0600