10.34. Shadow-4.2.1

The Shadow package contains programs for handling passwords in a secure way.

10.34.1. Installation of Shadow



If you would like to enforce the use of strong passwords, refer to http://cblfs.cross-lfs.org/index.php/Cracklib for installing Cracklib prior to building Shadow. After Cracklib is installed, execute this sed in Shadow's source directory to correct the path to the Cracklib dictionary:

sed -i 's@\(DICTPATH.\).*@\1/lib/cracklib/pw_dict@' etc/login.defs

Finally, add --with-libcrack to the configure command below.

Disable the installation of the groups and nologin programs and their man pages, as better versions of these programs are provided by Coreutils and Util-linux:

sed -i src/Makefile.in \
  -e 's/groups$(EXEEXT) //' -e 's/= nologin$(EXEEXT)/= /'
find man -name Makefile.in -exec sed -i \
  -e 's/man1\/groups\.1 //' -e 's/man8\/nologin\.8 //' '{}' \;

Prepare Shadow for compilation:

CC="gcc ${BUILD64}" ./configure --sysconfdir=/etc

The meaning of the new configure option:


Tells Shadow to install its configuration files into /etc, rather than /usr/etc.

Compile the package:


This package does not come with a test suite.

Install the package:

make install

Instead of using the default DES method, use the more secure SHA512 method of password encryption, which also allows passwords longer than 8 characters. It is also necessary to change the obsolete /var/spool/mail location for user mailboxes that Shadow uses by default to the /var/mail location used currently. Use the following sed command to make these changes to the appropriate configuration file:

sed -i /etc/login.defs \
    -e 's@#\(ENCRYPT_METHOD \).*@\1SHA512@' \
    -e 's@/var/spool/mail@/var/mail@'

Move a misplaced program to its proper location:

mv -v /usr/bin/passwd /bin

10.34.2. Configuring Shadow

This package contains utilities to add, modify, and delete users and groups; set and change their passwords; and perform other administrative tasks. For a full explanation of what password shadowing means, see the doc/HOWTO file within the unpacked source tree. If using Shadow support, keep in mind that programs which need to verify passwords (display managers, FTP programs, pop3 daemons, etc.) must be Shadow-compliant. That is, they need to be able to work with shadowed passwords.

To enable shadowed passwords, run the following command:


To enable shadowed group passwords, run:


To view or change the default settings for new user accounts that you create, you can edit /etc/default/useradd. See man useradd or http://cblfs.cross-lfs.org/index.php/Configuring_for_Adding_Users for more information.

10.34.3. Setting the root password

Choose a password for user root and set it by running:

passwd root

10.34.4. Contents of Shadow

Installed programs: chage, chfn, chgpasswd, chpasswd, chsh, expiry, faillog, gpasswd, groupadd, groupdel, groupmems, groupmod, grpck, grpconv, grpunconv, lastlog, login, logoutd, newgrp, newusers, passwd, pwck, pwconv, pwunconv, sg (link to newgrp), su, useradd, userdel, usermod, vigr (link to vipw), vipw
Installed directory: /etc/default

Short Descriptions


Used to change the maximum number of days between obligatory password changes


Used to change a user's full name and other information


Used to update group passwords in batch mode


Used to update the passwords of an entire series of user accounts


Used to change a user's default login shell


Checks and enforces the current password expiration policy


Is used to examine the log of login failures, to set a maximum number of failures before an account is blocked, or to reset the failure count


Is used to add and delete members and administrators to groups


Creates a group with the given name


Deletes the group with the given name


Allows a user to administer his/her own group membership list without the requirement of superuser privileges


Is used to modify the given group's name or GID


Verifies the integrity of the group files /etc/group and /etc/gshadow


Creates or updates the shadow group file from the normal group file


Updates /etc/group from /etc/gshadow and then deletes the latter


Reports the most recent login of all users or of a given user


Is used by the system to let users sign on


Is a daemon used to enforce restrictions on log-on time and ports


Is used to change the current GID during a login session


Is used to create or update an entire series of user accounts


Is used to change the password for a user or group account


Verifies the integrity of the password files /etc/passwd and /etc/shadow


Creates or updates the shadow password file from the normal password file


Updates /etc/passwd from /etc/shadow and then deletes the latter


Executes a given command while the user's GID is set to that of the given group


Runs a shell with substitute user and group IDs


Creates a new user with the given name, or updates the default new-user information


Deletes the given user account


Is used to modify the given user's login name, User Identification (UID), shell, initial group, home directory, etc.


Edits the /etc/group or /etc/gshadow files


Edits the /etc/passwd or /etc/shadow files