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Who am I?

From: Unix for Mac OS X Users

Video: Who am I?

In this chapter, we're going to talk about file ownership and privileges. Let's begin by making sure we can answer the question "who am I?" In chapter 1, we talked about how Unix is fundamentally designed to be a multiuser environment, and we've talked about how we log in each time we open a Terminal window. Now in Unix, a user is someone who has an account on the system and each user on the system wants to keep their private files private and only share certain files with others. Otherwise, if everyone has access to everything all the time ,then what's the point of even having logins and user accounts? So fundamental aspect of this multiuser environment is that a user has total access to their own files, limited access to other people's files, and so that we can have collaboration, we have the ability to grant permission to certain files to certain people.

Who am I?

In this chapter, we're going to talk about file ownership and privileges. Let's begin by making sure we can answer the question "who am I?" In chapter 1, we talked about how Unix is fundamentally designed to be a multiuser environment, and we've talked about how we log in each time we open a Terminal window. Now in Unix, a user is someone who has an account on the system and each user on the system wants to keep their private files private and only share certain files with others. Otherwise, if everyone has access to everything all the time ,then what's the point of even having logins and user accounts? So fundamental aspect of this multiuser environment is that a user has total access to their own files, limited access to other people's files, and so that we can have collaboration, we have the ability to grant permission to certain files to certain people.

Before we can do that though, we need to understand who we are and in Unix,= we can just simply type whoamI and it will tell you who you are. Now that may seem like a really sort of obvious answer because you're on your Mac. It's just you, you know you're logged in as you, but when you're working in Unix, it isn't always completely clear. You can actually switch users. We'll see how to do that little later. You may be logged into a remote Unix server like a web server. There are Web servers where I can log in as a specific user or I could login as root, and then it's important to know who am I right now.

If you can't do something that you think you ought to be able to do. If you can't open and read a file that you think you ought to have permission to read, well you can just type whoamI as a sort of sanity check to be like oh right, when I started this whole process, I logged in as a different user. I need to exit out and log back in as that other user or switch users so that then I have permission to do the thing that I want do. So it is an important concept in Unix. To keep most of the user's private files, each user gets a home directory. We saw that earlier. We used cd and then the twiddle or tilde as a shortcut and that's the shortcut to get to my home directory for kevin's home directory.

Whoever I'm logged in as that's where it's going to send me. Incidentally, that value is stored in home. So $home, that's where my home directory is. Each user has a different value when they logged in for home. For OS X those are located inside capital users and then the username. On a lot of other Unix systems, it will be home/ and then whatever the username is. So it will be something like that. So just to show you it's not there on the Mac, but that's where it'd live on the Unix systems. So now that we're clear on who we are right now, where we should be putting most of our private files, we are set up well to talk about the idea of file ownership and permission and how we go about changing those.

One thing that we touched on earlier that I want to make sure I mention again is that you can create other users. So you can go to your Apple menu > System Preferences and then from Accounts, you can click lock here to make changes and then click the plus sign and then you will be able to create new users. If you then want to switch and log out as a user, it'll quit all your programs and everything. So anything you have been working on will be gone, but what you'll do is from the Apple menu, you pick Log Out as that user. You don't have to shut down, you don't have to restart, you can just log out. Your Mac is still running. Unix is still running. You've just logged out as one user and it gives you the opportunity to log back in as a different user.

So you can try it out. You can create another user and you can try out a lot of the things that we're going to do here and you'll be able to see how the ownership and permissions affect things. Now you may not want to do that a lot because you are going to have to quit out of everything and then relaunch it all again, but it might be worth doing at some point during the exercises just to watch several of the movies in this chapter and then log out as one user, log back in as a different user, and see what you have the ability to do. Now some of you out there may be thinking "Well, I am the only user on my Mac and I'm always going to be the only user on my Mac and I am not going to work on any remote Unix servers or anything.

So I can skip all this. I don't need to know it." You can't. You really do need to still understand the idea of ownership and permissions because it's such a fundamental part of the way Unix works that you can't work in Unix without understanding how it works and how to manipulate them.

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This video is part of

Image for Unix for Mac OS X Users
Unix for Mac OS X Users

82 video lessons · 28402 viewers

Kevin Skoglund
Author

 
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  1. 3m 57s
    1. Introduction
      1m 14s
    2. Using the exercise files
      2m 43s
  2. 32m 2s
    1. What is Unix?
      7m 27s
    2. The terminal application
      4m 23s
    3. Logging in and using the command prompt
      5m 19s
    4. Command structure
      5m 22s
    5. Kernel and shells
      5m 25s
    6. Unix manual pages
      4m 6s
  3. 15m 58s
    1. The working directory
      2m 49s
    2. Listing files and directories
      3m 59s
    3. Moving around the filesystem
      4m 58s
    4. Filesystem organization
      4m 12s
  4. 1h 4m
    1. Naming files
      5m 41s
    2. Creating files
      2m 19s
    3. Unix text editors
      6m 39s
    4. Reading files
      5m 35s
    5. Reading portions of files
      3m 27s
    6. Creating directories
      2m 40s
    7. Moving and renaming files and directories
      8m 32s
    8. Copying files and directories
      3m 7s
    9. Deleting files and directories
      3m 38s
    10. Finder aliases in Unix
      4m 10s
    11. Hard links
      5m 30s
    12. Symbolic links
      6m 36s
    13. Searching for files and directories
      6m 32s
  5. 34m 58s
    1. Who am I?
      4m 3s
    2. Unix groups
      1m 52s
    3. File and directory ownership
      6m 41s
    4. File and directory permissions
      4m 27s
    5. Setting permissions using alpha notation
      6m 49s
    6. Setting permissions using octal notation
      3m 49s
    7. The root user
      1m 57s
    8. sudo and sudoers
      5m 20s
  6. 52m 34s
    1. Command basics
      4m 4s
    2. The PATH variable
      4m 13s
    3. System information commands
      3m 40s
    4. Disk information commands
      6m 8s
    5. Viewing processes
      5m 0s
    6. Monitoring processes
      3m 36s
    7. Stopping processes
      3m 19s
    8. Text file helpers
      6m 50s
    9. Utility programs
      7m 28s
    10. Using the command history
      8m 16s
  7. 20m 39s
    1. Standard input and standard output
      1m 24s
    2. Directing output to a file
      4m 13s
    3. Appending to a file
      2m 44s
    4. Directing input from a file
      5m 28s
    5. Piping output to input
      4m 40s
    6. Suppressing output
      2m 10s
  8. 41m 28s
    1. Profile, login, and resource files
      9m 11s
    2. Setting command aliases
      6m 59s
    3. Setting and exporting environment variables
      4m 54s
    4. Setting the PATH variable
      6m 10s
    5. Configuring history with variables
      6m 17s
    6. Customizing the command prompt
      6m 5s
    7. Logout file
      1m 52s
  9. 1h 25m
    1. grep: Searching for matching expressions
      5m 21s
    2. grep: Multiple files, other input
      4m 28s
    3. grep: Coloring matched text
      2m 57s
    4. Introduction to regular expressions
      3m 22s
    5. Regular expressions: Basic syntax
      3m 19s
    6. Using regular expressions with grep
      5m 20s
    7. tr: Translating characters
      8m 17s
    8. tr: Deleting and squeezing characters
      5m 30s
    9. sed: Stream editor
      7m 45s
    10. sed: Regular expressions and back-references
      7m 8s
    11. cut: Cutting select text portions
      7m 42s
    12. diff: Comparing files
      4m 35s
    13. diff: Alternative formats
      4m 30s
    14. xargs: Passing argument lists to commands
      7m 25s
    15. xargs: Usage examples
      7m 59s
  10. 42m 25s
    1. Finder integration
      4m 45s
    2. Clipboard integration
      5m 5s
    3. Screen capture
      3m 42s
    4. Shut down, reboot, and sleep
      3m 34s
    5. Text to speech
      2m 36s
    6. Spotlight integration: Searching metadata
      3m 41s
    7. Spotlight integration: Metadata attributes
      4m 24s
    8. Using AppleScript
      5m 23s
    9. System configurations: Viewing and setting
      5m 51s
    10. System configurations: Examples
      3m 24s
  11. 1m 26s
    1. Conclusion
      1m 26s

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