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File and directory permissions

File and directory permissions provides you with in-depth training on IT. Taught by Kevin Skoglund a… Show More

Unix for Mac OS X Users

with Kevin Skoglund

Video: File and directory permissions

File and directory permissions provides you with in-depth training on IT. Taught by Kevin Skoglund as part of the Unix for Mac OS X Users
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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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File and directory permissions
Video Duration: 4m 27s 6h 35m Beginner


File and directory permissions provides you with in-depth training on IT. Taught by Kevin Skoglund as part of the Unix for Mac OS X Users

View Course Description

Unix for Mac OS X Users unlocks the powerful capabilities of Unix that underlie Mac OS X, teaching how to use command-line syntax to perform common tasks such as file management, data entry, and text manipulation. The course teaches Unix from the ground up, starting with the basics of the command line and graduating to powerful, advanced tools like grep, sed, and xargs. The course shows how to enter commands in Terminal to create, move, copy, and delete files and folders; change file ownership and permissions; view and stop command and application processes; find and edit data within files; and use command-line shortcuts to speed up workflow. Exercise files accompany the course.

Topics include:
  • Moving around the file system
  • Creating and reading files
  • Copying, moving, renaming, and deleting files and directories
  • Creating hard links and symbolic links
  • Understanding user identity, file ownership, and sudo
  • Setting file permissions with alpha and octal notation
  • Changing the PATH variable
  • Using the command history
  • Directing input and output
  • Configuring the Unix working environment
  • Searching and replacing using grep and regular expressions
  • Manipulating text with tr, sed, and cut
  • Integrating with the Finder, Spotlight, and AppleScript
Mac OS X Unix

File and directory permissions

Now that we understand file and directory ownership, we are ready to look at file and directory permissions. The way that we see permissions is using the ls -la, just like we did for owner, to show us the full listing. Notice that I am already inside my user directory inside the unix_files folder. In this listing, we just got through talking about the owner column, the column where it says kevin over and over and then the one where it says staff that's the group column. What I want to talk about now is that very first block there, all the rws and dashes that are there. The very first character that you see we already said was an indicator of whether or not it's a directory, a file, or a link.

d for directory, dash for file, l for symbolic link. The next nine characters after that is a notation that indicates the permissions for each of these files and directories. So before we can go about changing the permissions, we need to understand what these symbols are trying to tell us about the current permissions. So we need to know how to decode them. We refer to this system as being alpha notation because we are using the alphabet to describe the different permissions. Imagine that we have three categories. We have our user. which is our owner category. We are going to call it user.

That's the first category. The second one is group, everyone who belongs to the group, and then the third category is other. That's everyone else who might have access to this file. So user, group, and other are our three categories. And for each of them we can set three kinds of permissions. We can set read permissions, whether or not you can read the contents of a file or a directory. write, whether or not we can actually make changes to a file or make changes to a directory. And then execute, which for a file would mean that we could run it like a program or a script. For a directory, it means that we can search inside of it.

That's what it means to be able to execute on a directory. Notice in this table that I've got yes's and no's, indicating which permissions I'd like to give each of these three categories. So I want the owner of the file to be able to read, write, and execute a file. The group, I'd like to just be able to read and write it. They can't execute it. For everyone else, they can only read it. I don't want them to make changes. So the only people should be able to make changes are the user and the group. So what we do for each of those, read, write, and execute, is we use the letter r, w, or x to indicate it and then we essentially add them up, so that what we end up with for the user is r, w, and x and they can do all three things.

The group is r and w, but not an x and we put a placeholder dash in place of it. For everyone else, they can only read. So they get r and two dashes. Notice now we have nine characters. You take all of those, you smash them together, and that is the nine-character permission string that we are seeing in our directory listing. So for example, if we take this file lorem_ipsum.txt, you can see that its permissions allow me, the owner, to read and write to the file but not execute it and that's fine. Frequently we don't have execute turned on for files because it's not a script. It's a text file.

We don't need to run this. We are just going to be reading and writing to it. For the group, which would be everyone in the group staff, which you'll remember included the other user I created, lynda, has the ability to read the file, but not to write to it or execute it, and then everyone else, everyone else who might ever come in contact with this file, is able to read it, but not to write and execute to it. Now you can see that, for example, that there is different permissions down here for the test directory. By default, directories are given the x so that they are searchable. It's essentially the same thing as being able to read, so we're able to search inside of it if we can read what's in it.

So, by default, when you create a directory, it will include that as well. But you can see that the group staff and everyone else can't write to this directory. They can just read it and search it. So let's see how this prevents people from having access. Let's take a look as a contrast. I have the other user on here, which is lynda, and now we can see the contents of her directory. Here is the directory. Remember this dot represents the current directory. So this is the directory we are looking at. We as part of her group have read and execute permissions on this directory. That's why we are able to see this listing.

Let's try now to do the same thing, but let's add pictures to begin. We are going to try and look at her vacation photos. Notice what the permissions are down here. She has read, write, and execute privileges, but that's it. No one else has any privileges. So if we hit Return, it says "Oops, permission denied." If we do cd into that folder, you will see it says "Nope sorry, you can't get in there, permission denied." So you see how it works. You see how these keep us from getting into other people's stuff. So we can see her user directory, but we're not able to go any deeper into her documents or her movies or her pictures or anything like that.

Find answers to the most frequently asked questions about Unix for Mac OS X Users .

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Q: The exercise files for the following movies appear to be broken:

Is there something wrong with them?
These exercises include one or more "dot files", whose file names start with a period. These files are normally hidden from view by the Finder.  So that they would show up in the Finder, the period has been removed from the file names. Additionally, "_example" has been added at the end of the file name to make it clear that the file will not work as-is. To make the dot files usable, either:

1) Open the file in a text editor to view its contents. Note that it may not be possible to double-click the file to open it because there is no file extension (such as .txt).
2) Resave the file under a new name (usually by choosing File > Save As), adding a "." to the beginning of the file name and removing "_example" from the end.


1) Copy and rename the file from the Unix command line using the techniques discussed in this course. Rename the file by adding a "." to the start and removing "_example" from the end. Include the "-i" option to prevent overwriting an existing file unexpectedly.
Example:  cp -i ~/Desktop/Exercise\ Files/Chapter_07/07_02_files/bashrc_example ~/.bashrc





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