Home > Articles > Operating Systems, Server > Linux/UNIX/Open Source

📄 Contents

  1. Beginning Your Session
  2. Seeing What's Going On Around You
  3. Summary
  4. Workshop
This chapter is from the book

Seeing What’s Going On Around You

You’re logged in, looking at the command prompt, and ready to delve into this Unix thing. Great! Let’s have a look.

Task 2.4: Who Are You?

While you’re logged in to the system, you can learn a few more Unix commands, including a couple that can answer a philosophical conundrum that has bothered men and women of thought for thousands of years: Who am I?

  1. The easiest way to find out “who you are” is to enter the whoami command:

    % whoami
    taylor
    %

    Try it on your system. The command lists the account name associated with the current login.

  2. Ninety-nine percent of the commands you type with Unix have a single specific spelling and will fail if you get creative. With whoami, however, adding spaces to transform the statement into proper English—that is, entering who am I—dramatically changes the result. On my system, I get the following results:

    % who am i
    taylor     pts/2        Oct 27 10:11    (:0.0)
    %

    On a Mac system, it doesn’t show (:0.0) otherwise things work well.

    This tells me quite a bit about my identity on the computer, including my account name and where and when I logged in. Try the command on your system to see what results you get.

    In this example, my account name is taylor. The pts/2 is the current communication line I’m using to access the system, and you can see that I logged in at 10:11 using a regular communications socket. (The :0.0 is relevant under the X Window System, something we won’t cover for quite a while in this book.)

  3. One of the most dramatic influences Unix systems have had on the computing community is the propensity for users to work together on a network, hooked up by telephone lines and modems (the predominant method until the middle to late 1980s) or by high-speed network connections to the Internet (a more common type of connection today). Regardless of the connection, however, you can see that each computer needs a unique identifier to distinguish it from others on the network. In the early days of Unix, systems had unique hostnames, but as hundreds of systems have grown into millions, this has proved to be an unworkable solution.
  4. The alternative was what’s called a domain-based naming scheme, where systems are assigned unique names within specific subsets of the overall network. Here’s an example:

    mentor.utech.edu

    The computer I use is within the .edu domain (read the hostname and domain—mentor.utech.edu—from right to left), meaning that the computer is located at an educational institution. Then, within the educational institution subset of the network, utech is a unique descriptor, and, therefore, if other UTech universities existed, they couldn’t use the same top-level domain name. Finally, mentor is the name of the computer itself.

  5. As with learning to read addresses on envelopes, learning to read domain names can unlock much information about a computer and its location. For example, lib.stanford.edu is the library computer at Stanford University, and ccgate.infoworld.com tells you that the computer is at InfoWorld, a commercial computer site, and that its hostname is ccgate. You’ll learn more about this later when you learn how to use electronic mail to communicate with people throughout the Internet.
  6. Another way to find out who you are in Unix is to use the id command. The purpose of this command is to tell you what group or groups you’re in and the numeric identifier for your account name (known as your user ID number or user ID). Enter id and see what you get. I get the following result:

    % id
    uid=100(taylor) gid=10(staff)
    %
  7. In this example, you can see that my account name is taylor and that the numeric equivalent, the user ID, is 100. (Here it’s abbreviated as uid—pronounce it “you-eye-dee” to sound like a Unix expert). Just as the account name is unique on a system, so also is the user ID. Fortunately, you rarely, if ever, need to know these numbers since they’re used by the OS internally, so focus on the account name and group name.
  8. Next, you can see that my group ID (or gid) is 10 and that group number 10 is known as the staff group. It’s the only group to which I belong.

    On another system, I am a member of two different groups:

    % id
    uid=103(taylor) gid=10(staff) groups=10(staff),44(ftp)
    %

    Although I have the same account name on this system (taylor), you can see that my user ID and group ID are both different from those in the earlier example. Note also that I’m a member of two groups: the staff group, with a group ID of 10, and the ftp group, with a group ID of 44.

You’ve now learned a couple different ways to have Unix give you some information about your account. Later, you’ll learn how to set protection modes on your files so that people in your group can read your files but so those not in your group are barred from access.

Task 2.5: Finding Out What Other Users Are Logged In to the System

The next philosophical puzzle that you can solve with Unix is “Who else is there?” The answer, however, is rather restricted, limited to only those people currently logged in to the same computer at the same time. Three commands are available to get you this information, and the one you choose depends on how much you’d like to learn about the other users: users, who, and w.

  1. The simplest of the commands is the users command, which lists the account names of all people using the system:

    % users
    david mark taylor
    %

    In this example, david and mark are also logged in to the system with me. Try this on your computer and see what other users—if any—are logged in to your computer system.

  2. A command that you’ve encountered earlier in this hour can be used to find out who is logged on to the system, what line they’re on, and how long they’ve been logged in. That command is who:

    % who
    taylor     vt/7         Oct 27 14:10    (:0)
    david      pts/1        Dec 27 15:54    (:0.0)
    mark       pts/2        Oct 27 11:51    (:0.0)
    %

    Here, you can see that three people are logged in: taylor (me), david, and mark. Furthermore, you can now see that david is logged in by connection pts/1 and has been connected since December 27 at 3:54 p.m. You can see that mark has been connected since just before noon on October 27 on line pts/2. Note that I have been logged in since 14:10, which is 24-hour time for 2:10 p.m. Unix doesn’t always indicate a.m. or p.m.

The user and who commands can tell you who is using the system at any particular moment, but how do you find out what they’re doing?

Task 2.6: What Is Everyone Doing on the Computer?

To find out what everyone else is doing, there’s a third command, w, that serves as a combination of “Who are they?” and “What are they doing?”

  1. Consider the following output from the w command:

    % w
    2:12pm  up 7 days,  5:28,  3 users, load average: 0.33, 0.33, 0.02
    User     tty           login@  idle   JCPU   PCPU  what
    taylor   vt/7         27Oct14         2:35   2:07  python2.6 /usr/lib/system-config
    david    pts/1         3:54pm   2:04    15     33  bash
    mark     pts/2        27Oct14     43               -csh
    %

    This is a much more complex command than users or who, and it offers more information. Notice that the output is broken into different areas. The first line summarizes the status of the system and, rather cryptically, the number of programs that the computer is running at one time. Finally, for each user, the output indicates the username, the tty, when the user logged in to the system, how long it’s been since the user has done anything (in minutes and seconds), the combined CPU time of all jobs the user has run, and the amount of CPU time taken by the current job. The last field tells you what you wanted to know in the first place: What are the users doing?

    In this example, the current time is 2:12 p.m., and the system has been up for 7 days, 5 hours, and 28 minutes. Currently three users are logged in, and the system is very quiet, with an average of 0.33 jobs submitted (or programs started) in the last minute; 0.33 jobs, on average, in the last 5 minutes; and 0.02 jobs in the last 15 minutes.

    taylor is the only user actively using the computer (that is, who has no idle time) and is using the python command. User david is sitting in the bash shell, which has gone for quite awhile without any input from the user (2 hours and 11 minutes of idle time). The program already has used 15 seconds of CPU time and, overall, david has used 33 seconds of CPU time. User mark has a C shell running, as indicated by -csh. (The leading dash indicates that this is the program that the computer launched automatically when mark logged in. This is akin to how the system automatically launches the Finder on a Macintosh.) User mark hasn’t actually done anything yet: Notice that there is no accumulated computer time for that account.

  2. Now it’s your turn. Try the w command on your system and see what kind of output you get. Try to interpret all the information based on the explanation here. One thing is certain: Your account should have the w command listed as what you’re doing.

On a multiuser Unix system, the w command gives you a quick and easy way to see what’s going on.

Task 2.7: Checking the Current Date and Time

You’ve learned how to orient yourself on a Unix system, and you are now able to figure out who you are, who else is on the system, and what everyone is doing. What about the current time and date?

  1. Logic suggests that time shows the current time and date the current date; but this is Unix, and logic doesn’t always apply. In fact, consider what happens when I enter time on my system:

    % time
    
    real    0m0.000s
    user    0m0.000s
    sys    0m0.000s
    %

    The output is cryptic to the extreme and definitely not what you’re interested in finding out. The program is showing how much user time, system time, and CPU time has been used by the command interpreter itself, broken down by input/output operations and more. (The time command is more useful than it looks, particularly if you’re a programmer.)

    On other Unixes, you might find time to be a missing command, a built-in shell function, or something completely different. In all cases, it won’t tell you the current time.

  2. Well, time didn’t work, so what about date?

    % date
    Sat Jun  617:05:32 MST 2015
    %

    That’s more like it!

    Try the date command on your computer and see whether the output agrees with your watch.

How do you think date keeps track of the time and date when you’ve turned off the computer? Does the computer know the correct time if you unplug it for a few hours? (I hope so. Almost all computers today have little batteries inside for just this situation.)

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