Home > Articles > Programming > Android

Time and Resource Limits

You may also wish to impose access time restrictions and resource limitations on your users. PAM affords the opportunity to impose such limitations through the modules pam_time and pam_limits, respectively.

Using pam_time This module is used with module type account only. Although it accepts no arguments, it does expect a configuration file, /etc/security/ time.conf (Red Hat 5.2/6.0; other distributions may vary), to supply it with login location and time limitations. The absence of this file has the effect of not restricting access in any way. The limitations apply to all users, including root.

Suppose that you'd like to impose some limits on user access to a particular system. Take a look at the account module type entries in Example 5-10. The pam_time and the pam_pwdb entries both use the control flag required. This has the effect of causing the account verification step to proceed. For example, if Mary's password has expired, when she attempts to log in, she will be so informed and refused access regardless of the limitations imposed by pam_time. Let's assume that Mary's password has expired and that she is attempting to connect to the system livfreeordie outside the limits imposed by /etc/security/time.conf (see The /etc/security/time.conf File on page 96). Example 5-11 shows what happens if Mary attempts to log in under these assumptions and /etc/pam.d/login is configured as shown in Example 5-10. Even though Mary is logging in outside of her approved time, the only information she gets is that her password has expired.

Example 5-10 Partial Configuration File Using pam_time required

Account  required  /lib/security/pam_pwdb.so
Account  required  /lib/security/pam_time.so

Example 5-11 Login Attempt with Expired Password and Outside of Permitted Times 1

$telnet livfreeordie
Escape character is '^]'.
Red Hat Linux release 5.2 (Apollo)
Kernel 2.0.36 on an i686
Your account has expired;please contact your system administrator
User account has expired
Connection closed by foreign host.

If you reverse the entries and set the control flag to requisite for pam_time, the behavior is quite different. Example 5-12 shows the new configuration. Example 5-13 shows what happens with the new configuration when Mary attempts to log in.

Example 5-12 Partial Configuration File Using pam_time.so requisite

Account  requisite  /lib/security/pam_time.so 
account  required  /lib/security/pam_pwdb.so 

Example 5-13 Login Attempt with Expired Password and Outside of Permitted Times 2

$ telnet livfreeordie
Escape character is '^]'.
Red Hat Linux release 5.2 (Apollo)
Kernel 2.0.36 on an i686
Permission denied
Connection closed by foreign host.

The moral of these examples is: watch your order and control flag settings. Experiment before you implement! Make sure the configuration settings provide the functionality you expect.

Next we turn our attention to the time.conf file.

The /etc/security/time.conf File. This file controls access time and login location by device when using the pam_time module. Each line in the file is a record, called a rule, except lines beginning with # which are comments. Each record has the following syntax:


This syntax is further detailed in Table 5.6.

The phrase logical list referenced in Table 5.6 means that the special characters, described in Table 5.7, are used as conditional operators

Logical operators may be mixed. For example, tty* & !ttyp* means that any serial device is allowed for this rule, but all pseudo-devices are not.

The syntax used to specify days in timed.conf is summarized in Table 5.8. These codes are then used with time ranges, all times being specified by the 24-hour clock. For example, Wd0800-1600 means weekends between the hours of 8 A.M. and 4 P.M.. Notice that there are no spaces between the day code and the time.

Table 5.6 Description of /etc/security/time.conf Entries




A logical list of the services associated with PAM. Multiple records with the same service are acceptable. Examples include login, rsh, and su.


A logical list of device(s). The login device is stored in PAM_TTY. Normally this includes such devices as tty1 and tty2 for the console, ttyS0 and ttyS1 for serial ports, and ttyp1 and ttyp2 for pseudo-devices normally associated with network and X Window connections.


A logical list of (valid) users. May include root.


A logical list of times at which this rule applies.

Table 5.7 Conditional Operators Used in /etc/security/time.conf





logical AND

user1 & user2—means this rule applies to both user1 and user2.


logical OR

tty1 | tty2—means this rule applies to either tty1 or tty2.


logical NOT

! login—this rule does not apply to the login service.



Matches any value, its meaning depending on its location in a field.

Table 5.8 Day Codes in /etc/security/timed.conf

Day Code


Mo, Tu, We, Th, Fr, Sa, Su

Each code individually applies to the day of the week it indicates. These codes may be concatenated; for example, MoTuWe means Monday, Tuesday, and Wednesday.

Wk and Wd

Wk means weekdays while Wd means weekends (Saturday and Sun-day). Note that, for example, MoWk means all weekdays except Monday.


All seven days. Note that, for example, AlSu means all days except Sunday.

Example 5-14 shows a series of entries in a sample /etc/security/ time.conf file. In this example, the root user has access to all services all of the time so long as root logs in from tty1. The users—joe, bill, and jane—have access every day of the week between 8 A.M. and 6 P.M. from any device so long as they connect via login or rsh. The user guest may log in from anywhere, Monday through Friday between the hours of 9 A.M. and 4 P.M., except between 12 noon and 1 P.M. Finally, any user may access the system using ftp from any source Monday through Friday between the hours of 9 A.M. and 4 P.M. All other users are unrestricted.

Example 5-14 Sample /etc/security/time.conf File

login ↱*;joe|bill|jane;Al0800-1800

This file is not order dependent. If there are entries that overlap, the least permissive (actually, the intersection of all entries) is used. Remember, you must place a pam_time entry in each file in /etc/pam.d for those services for which you want to restrict access. If you are going to limit access using pam_time, consider placing entries in at least the following files (and hence the associated services will be limited) in /etc/pam.d: ftp, login, ppp, rexec, rlogin, rsh, su, and xdm.


If you use an entry of the form *;*;*;!AL0000-24000 in the /etc/security/time.conf file, you will lock out all users, including root, from the system! Should you find yourself locked out of the system, see the section Recovering a Corrupt System on page 24 in Chapter 3 for recovery procedures.

Using pam_limits You may additionally restrict user accounts by imposing limits on the system resources available to each user login session. This may be useful in limiting system-based DoS attacks. The pam_limits module operates as a session module type only. It supports two arguments—debug and conf=/path/to/config_file (the default configuration file is /etc/security/ limits.conf). It does not impose any limits on the root account.

The /etc/security/limits.conf file is used to impose limits on a per-user or per-group basis. All limits specified apply to a single session. Each line in the file is a record, except for those beginning with #. The syntax of a record is

username|@groupname type resource limit

where username|@groupname specifies that either a username or a groupname preceded with @ may be used. The wildcard character * is acceptable and represents all users (hence all groups). The type field is either the hard or soft parameter; hard imposes a fixed limit and soft specifies a default limit. The resource parameter is one of the items described in Table 5.9. The limit parameter is the limit itself on the associated resource.

It is important to note that the limits imposed are on a per-session basis. The total limitation may be controlled with the maxlogins parameter. Limits may be completely disabled for particular users with the special character, -, an instance of which is shown in Example 5-15 . In this example, all users are limited to a resident set size of approximately 10 megabytes (MB) per session. All users may also have a maximum of only four simultaneous logins. It is this value that sets the overall maximum per user. The user, bin, has all limits disabled, including the previous entries in the file. The remaining limitations in the file are additional limitations for the users and groups indicated. The user ftp is allowed only 10 logins (this is an excellent limit to impose on anonymous ftp accounts since it limits the number of simultaneous logins). All users in the group managers have a process limitation of 40 and all users in the group developers have a memlock limit of approximately 64 MB.

Example 5-15 Sample /etc/security/limits.conf File

*      hard  rss     10000
*      hard  maxlogins  4
bin     -	
ftp     hard  maxlogins  10
@managers  hard  nproc    40
@developers hard  memlock   64000

Table 5.9 Limitable Resources in /etc/security/limits.conf




Limits the size of a core file (KB*)


Maximum data size (KB)


Maximum file size (KB)


Maximum locked-in memory address space (KB)


Maximum number of open files


Maximum resident set size (KB)


Maximum stack size (KB)


Maximum CPU time in minutes


Maximum number of processes


Address space limit


Maximum number of logins allowed for this user

Of course, you must determine the limits necessary for each system at your site. Make sure you place the entry session required /lib/security/pam_limits.so in each appropriate file in /etc/pam.d.

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.


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.


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.


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.


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


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


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.


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.


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