Shadow-4.0.4.1
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## Shadow-4.0.4.1

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

    Approximate build time:  0.4 SBU
    Required disk space:     11 MB

Shadow installation depends on: Bash, Binutils, Bison, Coreutils, Diffutils, GCC, Gettext, Glibc, Grep, Make, Sed.

### Installation of Shadow

Shadow hard-wires the path to the passwd binary within the binary itself, but does this the wrong way. If a passwd binary is not present before installing Shadow, the package incorrectly assumes it is going to be located at `/bin/passwd`, but then installs it as `/usr/bin/passwd`. This will lead to errors about not finding `/bin/passwd`. To work around this bug, create a dummy `passwd` file, so that it gets hard-wired properly:

    touch /usr/bin/passwd

Now prepare Shadow for compilation:

    ./configure --libdir=/usr/lib --enable-shared

Work around a problem that prevents Shadow's internationalization from working:

    echo '#define HAVE_SETLOCALE 1' >> config.h

Compile the package:

    make

Then install it:

    make install

Shadow uses two files to configure authentication settings for the system. Install these two config files:

    cp etc/{limits,login.access} /etc

Instead of using the default crypt method, we want to use the more secure MD5 method of password encryption, which also allows passwords longer than 8 characters. We also need to change the obsolete `/var/spool/mail` location for user mailboxes that Shadow uses by default to the `/var/mail` location used currently. We accomplish both these things by changing the relevant configuration file while copying it to its destination (it's probably better to cut-and-paste this rather than try and type it all in):

    sed -e 's%#MD5_CRYPT_ENAB.no%MD5_CRYPT_ENAB yes%' \
        -e 's%/var/spool/mail%/var/mail%' \
        etc/login.defs.linux > /etc/login.defs

Move some misplaced symlinks to their proper locations:

    mv /bin/sg /usr/bin
    mv /bin/vigr /usr/sbin

And move Shadow's dynamic libraries to a more appropriate location:

    mv /usr/lib/lib{shadow,misc}.so.0* /lib

As some packages expect to find the just-moved libraries in `/usr/lib`, create the following symlinks:

    ln -sf ../../lib/libshadow.so.0 /usr/lib/libshadow.so
    ln -sf ../../lib/libmisc.so.0 /usr/lib/libmisc.so

The -D option of the `useradd` program requires this directory for it to work properly:

    mkdir /etc/default

Coreutils has already installed a better groups program in `/usr/bin`. Remove the one installed by Shadow:

    rm /bin/groups

### Configuring Shadow

This package contains utilities to add, modify and delete users and groups, set and change their passwords, and other such administrative tasks. For a full explanation of what password shadowing means, see the `doc/HOWTO` file within the unpacked source tree. There's one thing to keep in mind if you decide to use Shadow support: programs that need to verify passwords (display managers, ftp programs, pop3 daemons, and the like) need to be shadow-compliant, that is they need to be able to work with shadowed passwords.

To enable shadowed passwords, run the following command:

    pwconv

To enable shadowed group passwords, run:

    grpconv

Under normal circumstances, you won't have created any passwords yet. However, if returning to this section later to enable shadowing, you should reset any current user passwords with the passwd command or any group passwords with the gpasswd command.

### Setting the root password

Choose a password for user root and set it via:

    passwd root

### Contents of Shadow

Installed programs: chage, chfn, chpasswd, chsh, dpasswd, expiry, faillog, gpasswd, groupadd, groupdel, groupmod, groups, grpck, grpconv, grpunconv, lastlog, login, logoutd, mkpasswd, newgrp, newusers, passwd, pwck, pwconv, pwunconv, sg (link to newgrp), useradd, userdel, usermod, vigr (link to vipw) and vipw

### Short descriptions

chage is used to change the maximum number of days between obligatory password changes.

chfn is used to change a user's full name and some other info.

chpasswd is used to update the passwords of a whole series of user accounts in one go.

chsh is used to change a user's default login shell.

dpasswd is used to change dial-up passwords for user login shells.

expiry checks and enforces the current password expiration policy.

faillog 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.

gpasswd is used to add and delete members and administrators to groups.

groupadd creates a group with the given name.

groupdel deletes the group with the given name.

groupmod is used to modify the given group's name or GID.

groups reports the groups of which the given users are members.

grpck verifies the integrity of the group files, `/etc/group` and `/etc/gshadow`.

grpconv creates or updates the shadow group file from the normal group file.

grpunconv updates `/etc/group` from `/etc/gshadow` and then deletes the latter.

lastlog reports the most recent login of all users, or of a given user.

login is used by the system to let users sign on.

logoutd is a daemon used to enforce restrictions on log-on time and ports.

mkpasswd encrypts the given password using the also given perturbation.

newgrp is used to change the current GID during a login session.

newusers is used to create or update a whole series of user accounts in one go.

passwd is used to change the password for a user or group account.

pwck verifies the integrity of the password files, `/etc/passwd` and `/etc/shadow`.

pwconv creates or updates the shadow password file from the normal password file.

pwunconv updates `/etc/passwd` from `/etc/shadow` and then deletes the latter.

sg executes a given command while the user's GID is set to that of the given group.

useradd creates a new user with the given name, or updates the default new-user information.

userdel deletes the given user account.

usermod is used to modify the given user's login name, UID (User Identification), shell, initial group, home directory, and the like.

vigr can be used to edit the `/etc/group` or `/etc/gshadow` files.

vipw can be used to edit the `/etc/passwd` or `/etc/shadow` files.

libmisc...

libshadow contains functions used by most programs in this package.

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