8.26. Shadow-4.13

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

Approximate build time: 0.1 SBU
Required disk space: 46 MB

8.26.1. Installation of Shadow



If you would like to enforce the use of strong passwords, refer to https://www.linuxfromscratch.org/blfs/view/systemd/postlfs/cracklib.html for installing CrackLib prior to building Shadow. Then add --with-libcrack to the configure command below.

Disable the installation of the groups program and its man pages, as Coreutils provides a better version. Also, prevent the installation of manual pages that were already installed in Section 8.3, “Man-pages-6.05.01”:

sed -i 's/groups$(EXEEXT) //' src/Makefile.in
find man -name Makefile.in -exec sed -i 's/groups\.1 / /'   {} \;
find man -name Makefile.in -exec sed -i 's/getspnam\.3 / /' {} \;
find man -name Makefile.in -exec sed -i 's/passwd\.5 / /'   {} \;

Instead of using the default crypt method, use the much more secure YESCRYPT 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. And, remove /bin and /sbin from the PATH, since they are simply symlinks to their counterparts in /usr.



If you wish to include /bin and/or /sbin in the PATH for some reason, modify the PATH in .bashrc after LFS has been built.

    -e 's:/var/spool/mail:/var/mail:'                   \
    -e '/PATH=/{s@/sbin:@@;s@/bin:@@}'                  \
    -i etc/login.defs


If you chose to build Shadow with Cracklib support, issue this command:

sed -i 's:DICTPATH.*:DICTPATH\t/lib/cracklib/pw_dict:' etc/login.defs

Prepare Shadow for compilation:

touch /usr/bin/passwd
./configure --sysconfdir=/etc   \
            --disable-static    \
            --with-{b,yes}crypt \

The meaning of the new configuration options:

touch /usr/bin/passwd

The file /usr/bin/passwd needs to exist because its location is hardcoded in some programs; if it does not already exist, the installation script will create it in the wrong place.


The shell expands this to two switches, --with-bcrypt and --with-yescrypt. They allow shadow to use the Bcrypt and Yescrypt algorithms implemented by Libxcrypt for hashing passwords. These algorithms are more secure (in particular, much more resistant to GPU-based attacks) than the traditional SHA algorithms.


The longest permissible user name is 32 characters. Make the maximum length of a group name the same.

Compile the package:


This package does not come with a test suite.

Install the package:

make exec_prefix=/usr install
make -C man install-man

8.26.2. 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 you use 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 must be able to work with shadowed passwords.

To enable shadowed passwords, run the following command:


To enable shadowed group passwords, run:


Shadow's default configuration for the useradd utility needs some explanation. First, the default action for the useradd utility is to create the user and a group with the same name as the user. By default the user ID (UID) and group ID (GID) numbers will begin at 1000. This means if you don't pass extra parameters to useradd, each user will be a member of a unique group on the system. If this behavior is undesirable, you'll need to pass either the -g or -N parameter to useradd, or else change the setting of USERGROUPS_ENAB in /etc/login.defs. See useradd(8) for more information.

Second, to change the default parameters, the file /etc/default/useradd must be created and tailored to suit your particular needs. Create it with:

mkdir -p /etc/default
useradd -D --gid 999

/etc/default/useradd parameter explanations


This parameter sets the beginning of the group numbers used in the /etc/group file. The particular value 999 comes from the --gid parameter above. You may set it to any desired value. Note that useradd will never reuse a UID or GID. If the number identified in this parameter is used, it will use the next available number. Note also that if you don't have a group with an ID equal to this number on your system, then the first time you use useradd without the -g parameter, an error message will be generated—useradd: unknown GID 999, even though the account has been created correctly. That is why we created the group users with this group ID in Section 7.6, “Creating Essential Files and Symlinks”.


This parameter causes useradd to create a mailbox file for each new user. useradd will assign the group ownership of this file to the mail group with 0660 permissions. If you would rather not create these files, issue the following command:

sed -i '/MAIL/s/yes/no/' /etc/default/useradd

8.26.3. Setting the Root Password

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

passwd root

8.26.4. Contents of Shadow

Installed programs: chage, chfn, chgpasswd, chpasswd, chsh, expiry, faillog, getsubids, gpasswd, groupadd, groupdel, groupmems, groupmod, grpck, grpconv, grpunconv, lastlog, login, logoutd, newgidmap, newgrp, newuidmap, newusers, nologin, passwd, pwck, pwconv, pwunconv, sg (link to newgrp), su, useradd, userdel, usermod, vigr (link to vipw), and vipw
Installed directories: /etc/default and /usr/include/shadow
Installed libraries: libsubid.so

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 user passwords in batch mode


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, and to reset the failure count


Is used to list the subordinate id ranges for a user


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 super user 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 set the gid mapping of a user namespace


Is used to change the current GID during a login session


Is used to set the uid mapping of a user namespace


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


Displays a message saying an account is not available; it is designed to be used as the default shell for disabled 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 specified 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


library to handle subordinate id ranges for users and groups