Home > Articles > Programming > Android

PAM and login

The /etc/pam.d/login configuration file is read by Linux-PAM whenever the login (/bin/login) program is executed. Example 5-8 is a sample of this file. From the previous section, we have a good idea of what is going on here. Let's examine the details of the action of each module type.

Example 5-8 Sample /etc/pam.d/login File

Auth   required  /lib/security/pam_securetty.so
Auth   required  /lib/security/pam_pwdb.so
Auth   required  /lib/security/pam_nologin.so
Account  required  /lib/security/pam_pwdb.so
Password required  /lib/security/pam_cracklib.so minlen=20
     retry=3 type=SECRET
password required  /lib/security/pam_pwdb.so md5 use_authtok
session  required  /lib/security/pam_pwdb.so

Module Type auth There are three modules stacked for type auth. The first is pam_securetty. This is an auth module type only. It accepts no arguments. Its sole purpose is to check /etc/securetty against the device of the login attempt, if the user logging in is root. It will fail only if someone is trying to log in as root from a device not in /etc/securetty. Since this module is required, a failure here would cause the login to fail. Recall, however, that the control flag, required, will still allow subsequent modules to be executed, and therefore the user will not be refused access until after all three modules in this stack are executed.

The second module is pam_pwdb. As discussed in PAM and Passwords on page 86, its role here is to authenticate the user.

The third module in the stack is pam_nologin. This is also an auth-only module type that accepts no arguments. Its purpose is to check for the existence of /etc/nologin. If /etc/nologin exists, then no users, except root, are allowed to log in; if /etc/nologin contains a message, it is displayed. For example, if the /etc/nologin is then Example 5-9 exhibits the system's behavior when the user joe attempts to telnet to the system.

Example 5-9 Attempted Login with the Presence of /etc/nologin

$telnet livfreeordie
Trying 10.1.1.1...
Connected to livfreeordie.
Escape character is '^]'.
Red Hat Linux release 5.2 (Apollo)
Kernel 2.0.36 on an i686
login:joe
Password:
System down for maintenance until 2/28/99 at 4pm
Login incorrect
login:

OH, BY THE WAY...

Did you ever wonder about how to get rid of the message that appears when you connect to a system? In Example 5-9, it is the two-line message beginning with "Red Hat Linux." This message gives away information about your system, which does not reflect good security practice. On Red Hat 5.2/6.0, the message displayed reflects the contents of /etc/issue.net for remote connections and /etc/issue for local connections. At this point, you may be tempted to rush off and modify these files to suit your needs. Don't. The files are rewritten at every reboot! In order to modify these files, you must modify /etc/rc.d/rc.local. /etc/rc.d/rc2.d/S99local is a symbolic link to /etc/rc.d/rc.local, which is executed upon entering run level 2. Be sure to replace this message with something appropriate, maybe something like "This is a restricted system. All activities are logged." But whatever you do, don't reveal the operating system, hardware, or other information that may be used against you. And don't use words like "Welcome"! There are many other ways to replace this message, some of which will be discussed at various points in this text.

By default, Joe will actually be able to attempt to log in three more times, but of course the result will be the same. Existing login sessions are not affected by the /etc/nologin file.

This file is normally used for purposes of system maintenance, but it also is beneficial in case of a system breach. This topic is discussed in Chapter 3.

Normally, the /etc/nologin file does not exist and the user, once authenticated, will be granted access. The subsequent modules in /etc/pam.d/login are then invoked.

Module Types account, password, and session The pam_pwdb entry for the account module type, as previously described, performs the task of checking the user's account. If the user's password has expired, for example, the entries with module type password will be invoked and the events described in PAM and Passwords on page 86 will occur. The session entry is for the exclusive purpose of logging connection information to syslog.

Many other PAM configuration files besides /etc/pam.d/login incorporate the use of these modules and module types. Since each configuration file represents an application, it follows that any application that requires authentication by password will incorporate some or all of the modules and module types in /etc/pam.d/login. Included among these are rsh, rlogin, su, ppp, chfn, chsh, and ftp. Bear this in mind whenever you decide to make changes to one of these configuration files. For continuity, and for security, you will ordinarily make changes across the board. Think carefully if you decide not to change a particular configuration file whenever you change others.

Next let's take a look at some additional restrictions that may be imposed through PAM.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020