8.25. Shadow-4.11.1

#### Linux From Scratch - Version 11.1

### Chapter 8. Installing Basic System Software

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# 8.25. Shadow-4.11.1

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

Approximate build time: 0.2 SBU
Required disk space: 49 MB

## 8.25.1. Installation of Shadow

### Note

If you would like to enforce the use of strong passwords, refer to https://www.linuxfromscratch.org/blfs/view/11.1/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-5.13”:

    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 more secure SHA-512 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, get rid of `/bin` and `/sbin` from `PATH`, since they are simply symlinks to their counterpart in `/usr`.

### Note

If `/bin` and/or `/sbin` are preferred to be left over in `PATH` for some reason, modify `PATH` in `.bashrc` after LFS is built.

    sed -e 's:#ENCRYPT_METHOD DES:ENCRYPT_METHOD SHA512:' \
        -e 's:/var/spool/mail:/var/mail:'                 \
        -e '/PATH=/{s@/sbin:@@;s@/bin:@@}'                \
        -i etc/login.defs

### Note

If you chose to build Shadow with Cracklib support, run the following:

    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-group-name-max-length=32

The meaning of the configure option:

touch /usr/bin/passwd

  The file `/usr/bin/passwd` needs to exist because its location is hardcoded in some programs, and if it does not exist, the default location is not right.

`--with-group-name-max-length=32`

  The maximum user name is 32 characters. Make the maximum group name the same.

Compile the package:

    make

This package does not come with a test suite.

Install the package:

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

## 8.25.2. 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:

    pwconv

To enable shadowed group passwords, run:

    grpconv

Shadow's default configuration for the useradd utility has a few caveats that need some explanation. First, the default action for the useradd utility is to create the user and a group of the same name as the user. By default the user ID (UID) and group ID (GID) numbers will begin with 1000. This means if you don't pass 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 one of the `-g` or `-N` parameter to useradd or to 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` needs to 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

`GROUP=999`

  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 can modify it to anything you desire. 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 the first time you use useradd without the `-g` parameter, you will get a message displayed on the terminal that says: `useradd: unknown GID 999`, although the account is correctly created. That is why we have created the group `users` with this group ID in Section 7.6, “Creating Essential Files and Symlinks”.

`CREATE_MAIL_SPOOL=yes`

  This parameter causes useradd to create a mailbox file for the newly created user. useradd will make the group ownership of this file to the `mail` group with 0660 permissions. If you would prefer that these mailbox files are not created by useradd, issue the following command:

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

## 8.25.3. Setting the root password

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

    passwd root

## 8.25.4. 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 directory: /etc/default
Installed libraries: libsubid.so

### Short Descriptions

chage | Used to change the maximum number of days between obligatory password changes
chfn | Used to change a user's full name and other information
chgpasswd | Used to update group passwords in batch mode
chpasswd | Used to update user passwords in batch mode
chsh | Used to change a user's default login shell
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
getsubids | Is used to list the subordinate id ranges for a user
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
groupmems | Allows a user to administer his/her own group membership list without the requirement of super user privileges.
groupmod | Is used to modify the given group's name or GID
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
newgidmap | Is used to set the gid mapping of a user namespace
newgrp | Is used to change the current GID during a login session
newuidmap | Is used to set the uid mapping of a user namespace
newusers | Is used to create or update an entire series of user accounts
nologin | Displays a message that an account is not available; it is designed to be used as the default shell for accounts that have been disabled
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
su | Runs a shell with substitute user and group IDs
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, User Identification (UID), shell, initial group, home directory, etc.
vigr | Edits the `/etc/group` or `/etc/gshadow` files
vipw | Edits the `/etc/passwd` or `/etc/shadow` files
`libsubid` | library for process subordinate id ranges for users

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