Home > Articles > Operating Systems, Server

This chapter is from the book

Communicate over a Network

Many commands that you can use to communicate with other users on a single computer system have been extended to work over a network. Three examples of extended utilities, all of which were introduced in Chapter 3, are electronic mail programs (such as pine), information-gathering utilities (such as finger), and communications utilities (such as talk). These utilities are examples of the UNIX philosophy: Instead of creating a new, special-purpose tool, modify an existing one.

Many utilities understand a convention for the format of network addresses: user@host (spoken as user at host). When you use an @ sign in an argument to one of these utilities, the utility interprets the text that follows as the name of a remote host. When it does not include an @ sign, a utility assumes that you are requesting information from or corresponding with someone on your LAN.

The prompts shown in the examples in this chapter include the hostname of the machine you are using. When you frequently use more than one system over a network, you may find it difficult to keep track of which system you are using at any particular moment. If you set your prompt to include the hostname of the current system, it will always be clear which system you are using. To identify the computer you are using, run hostname or uname –n:

$ hostname 

See pages 579 bashtcsh.gif and 749 zsh.gif for information on how you can change your prompt.

finger :Displays Information about Remote Users

The finger utility displays information about one or more users on a system. This utility was designed for local use, but when networks became popular, it was obvious that finger should be enhanced to reach out and collect information remotely. In the following examples, finger displays information about all the users logged in on the system named bravo:

[kudos]$ finger @bravo 
Login     Name             Tty   Idle  Login Time   Office    Office Phone
root       root             *1    1:35  Oct 22  5:00
alex       Alex Watson       4           Oct 22 12:23 (kudos)
alex       Alex Watson       5       19  Oct 22 12:33 (:0)
jenny      Jenny Chen        7     2:24  Oct 22  8:45 (:0)
hls        Helen Simpson     11      2d  Oct 20 12:23 (:0)

A user's login name in front of the @ sign causes finger to display information from the remote system for the specified user only. If there are multiple matches for that name on the remote system, finger displays the results for all of them.

[kudos]$ finger alex@bravo 
Login     Name             Tty   Idle  Login Time   Office    Office Phone
alex      Alex Watson        4           Oct 22 12:23 (kudos)
alex      Alex Watson        5       19  Oct 22 12:33 (:0)

The finger utility works by querying a standard network service, the fingerd daemon, that runs on the system being queried. Although this service is supplied with Red Hat Linux, some sites choose not to run it to minimize the load on their systems, reduce security risks, or maintain privacy. When you use finger to obtain information about someone at such a site, you will see an error message or nothing at all. It is the remote fingerd daemon that determines how much information to share with your system and in what format. As a result, the report displayed for any given system may differ from the preceding examples.

SECURITY: The fingerd Daemon

The finger daemon (fingerd) gives away system account information that can aid a malicious user. Some sites disable finger or randomize user account IDs to make a malicious user's job more difficult. Disable finger by giving the following command as root: chkconfig finger off.

The information for remote finger looks much the same as it does when finger runs on your local system, with one difference: Before displaying the results, finger reports the name of the remote system that answered the query (bravo, as shown in brackets in the preceding example). The name of the host that answers may be different from the system name you specified on the command line, depending on how the finger daemon service is configured at the remote end. In some cases several hostnames may be listed if one finger daemon contacts another to retrieve the information.

Sending Mail to a Remote User

Given a user's login name on a remote system and the name of the remote system or its domain, you can use an e-mail program, such as pine (page 87), to send a message over the network or the Internet, using the @ form of an address:




Although the @ form of a network address is recognized by many GNU/Linux utilities, you may find that you can reach more remote computers with e-mail than with the other networking utilities described in this chapter. The reason for this disparity is that the mail system can deliver a message to a host that does not run IP, even though it appears to have an Internet address. The message may be routed over the network, for example, until it reaches a remote system that has a point-to-point, dial-up connection to the destination system. Other utilities, such as talk, rely on IP and operate only between networked hosts.

Mailing List Servers

A mailing list server (listserv14) allows you to create, manage, and administrate an e-mail list. An electronic mailing list provides a means for people interested in a topic to participate in an electronic discussion and for a person to disseminate information periodically to a potentially large mailing list. One of the most powerful features of most list servers is the ability to archive e-mail postings to the list, create an archive index, and allow users to retrieve postings from the archive based on keywords or discussion threads. Typically you can subscribe and unsubscribe from the list with or without human intervention. The owner of the list can restrict who can subscribe, unsubscribe, and post messages to the list. Popular list servers include LISTSERV (www.lsoft.com), Lyris (www.lyris.com), Majordomo (www.greatcircle.com/majordomo), Mailman (www.list.org), and ListProc (www.listproc.net). Red Hat maintains several mailing lists (https://listman.redhat.com) and list archives (www.redhat.com/mailing-lists). Use a browser to search on linux mailing list to find (many) other lists.

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