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Unix for Mac OS X Users
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Viewing processes


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Unix for Mac OS X Users

with Kevin Skoglund

Video: Viewing processes

Over the course of the next few movies I want to take a look at some Unix commands for managing processes. Think back to Chapter 1 where we talked about the difference between the kernel and the shell. In our case the shell is bash. Whenever we run a command inside our shell, a file executes and it communicates with the kernel. And essentially it says to the kernel, "Hey kernel! There are some things I need to accomplish here. Can you help me out?" The kernel sets aside some memory space and starts a process running in it. Then whenever there's output from that process, it returns it back to the shell for us to see. And whenever the process is finally done, the kernel then closes it out and reclaims that memory space so that it can be used by other processes.
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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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Unix for Mac OS X Users
6h 35m Beginner Apr 29, 2011

Viewers: in countries Watching now:

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
Subjects:
Developer Web
Software:
Mac OS X Unix
Author:
Kevin Skoglund

Viewing processes

Over the course of the next few movies I want to take a look at some Unix commands for managing processes. Think back to Chapter 1 where we talked about the difference between the kernel and the shell. In our case the shell is bash. Whenever we run a command inside our shell, a file executes and it communicates with the kernel. And essentially it says to the kernel, "Hey kernel! There are some things I need to accomplish here. Can you help me out?" The kernel sets aside some memory space and starts a process running in it. Then whenever there's output from that process, it returns it back to the shell for us to see. And whenever the process is finally done, the kernel then closes it out and reclaims that memory space so that it can be used by other processes.

That's what the kernel does. it manages the processes for us. Now we can have processes that are really short, like when we run the echo command. That's a really, really short process. It starts, it does its thing, and then it's over. We could also have longer running processes. Let's say that we're going to print five pages to a printer. That'll start a process and that process will just feed information to the printer. After it submits page 1, it'll go to page 2, and so on. And if the printer runs out of paper, the printer will communicate that back to the process, which will then let us know that the printer has run out of paper. That's an example of a long-running process.

We can also have background processes. For example, if we have a database server like MySQL running, it'll just sit and run in the background waiting for connections, waiting for someone to make a request to it which it'll then respond to. So it just sits in the background waiting to do its thing. Now what we want to do now is be able to see those processes. And the easiest way to do that is with the ps command. So ps stands for process status, and it's essentially giving us a snapshot of the processes that are running. Now there are lots of processes running on my machine. By default what ps is showing me are processes that are owned by me, the user kevin, and also a process which have a controlling terminal.

That is, I am in control of them. They're not background processes. If we want to see processes that are owned by other users as well, we can say ps -a. Still I am not seeing background processes but now I see processes that are not owned by me. Notice that the third line there lists the process they I just ran. ps -a. It's a process that's not owned by me. I own the bash process. Bash started the ps -a running, but it's actually a process that's owned by root. And when it's done doing its thing, it returns the results back to me. So it's a bit of a technical point but we don't necessarily own all the processes that get started.

A lot of times process gets started on our behalf by the kernel, which is acting as root. Now there's one big quirk about ps that you need to know about and that is that because ps has been around a long time and it has been modified in different versions of Unix, there's been a real effort to maintain some backwards compatibility here. So in addition to ps -a, we also can use ps a, without the dash. One is the classic option passed into the command that we've been seeing. The other one is using more like an argument that's being passed in. And you'll see that it gives us very similar results, not exactly the same but very similar.

What we're essentially seeing here are two different implementations of ps. One from one version of Unix and one from another. The reason I mention this is because the most classic way to use ps is ps with aux. Those are the options that we pass in and we typically don't put the hyphen in front it. It's a bit of an odd bird because it doesn't match the options that we're normally used to using with the dash. We can actually do a and x together but the problem is u, because u actually has a different meaning between the two versions, so therefore we can't do it that way.

So we're going to do it this way. a means show me all processes regardless of who they're owned by, u says include a column showing me the user that owns the process, and x says show me the background processes too. That's what those three options mean. Let's take a look at it. ps -aux, and there's a list of all the processes that I have running right now. Let's scroll up the top and take look at the header information. You can see that first column is the User, then is the Process ID. Every process gets assigned a unique ID number to help us keep track of it. It shows us the percentage of the CPU that's being used, the percentage of the memory that's being used.

This is the amount of virtual memory that's taking up. This is showing us the Terminal. In most cases it's a question mark. That often means that Mac OS X launched it. If we scroll down to the bottom you'll see that these processes that we've been working with have 000. That's for our current Terminal. If we own up a new window and ran commands there it would be 001. So let's go back to the top again. We have the status. You don't need to worry about those codes. The time that it started, the amount of time that it's been running, and then the command itself, which is a path to the file where this command got started.

So that gives you some information to browse over and you can see what's going on in your Mac. Now if you want to use other options, the man pages can give you a lot more of those information about them. But the most common way that you'll see it use is ps aux, and that should return a list like this. It'll show you a snapshot of what's happening with different processes at this moment in time. Now the problem with that is that it is a snapshot, and things change. things are constantly changing. And it'll be great if we had something where we can actually watch things like CPU and memory usage as they change over time. And to do that, we've got to use the top command which we'll see in the next movie.

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:
07_02_files
07_03_files
07_04_files
07_05_files
08_03_files

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.

OR

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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