Thanks to everyone that made it to our second session. Here's some follow-up stuff. I'm putting up text and links first, with diagrams, charts, and tables before the end of the week. Okay, here we go.

Thanks to everyone that made it to our second session. Here's some follow-up stuff. Here we go.

One item of note in the presentation was learning how a permisson change, on the execute bit, affects files and directories differently. This bit allows files, such as shell scripts, the ability to be run, or executed. Directories, on the other hand, are granted the abilty to execute a command that accesses the index of information about files that reside in the directory. This index is referred to as an inode, and it contains all of the statistics about the file it is associated with. For mor info about inodes, try this link.

One item of note in the presentation was learning how a permisson change, on the execute bit, affects files and directories differently. This bit allows files, such as shell scripts, the ability to be run, or executed. Directories, on the other hand, are granted the abilty to execute a command that accesses the index of information about files that reside in the directory. This index is referred to as an inode, and it contains all of the statistics about the file it is associated with. It is important to know understand this behavior, because an improperly set execute bit in a directory could return incomplete information about files you otherwise have access to. Any utility that checks queries a directory about it's contents would be affected. In our class we used ls -al as an example.

For more info about inodes, try this definition.

Inode Defined

Source http://www.linuxforum.com/linux-filesystem/glossary.html

It is important to know understand this behavior, because an improperly set execute bit in a directory could return incomplete information about files you otherwise have access to. Any utility that checks queries a directory about it's contents would be affected. In our class we used ls -al as an example.

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Review Material

Quick Reference

Probably above all else, it is a good idea to list the sites that I refer to in the class.

• File Permissions Tutorials
  • https://www.cae.wisc.edu/fsg/linux/linux-filepermissions.html

• • http://www.krnlpanic.com/tutorials/permissions.php

• How to count to seven, in binary
  • http://www.johnselvia.com/binary/bin1-7.html

About files and directories

One item of note in the presentation was learning how a permisson change, on the execute bit, affects files and directories differently. This bit allows files, such as shell scripts, the ability to be run, or executed. Directories, on the other hand, are granted the abilty to execute a command that accesses the index of information about files that reside in the directory. This index is referred to as an inode, and it contains all of the statistics about the file it is associated with. For mor info about inodes, try this link.

It is important to know understand this behavior, because an improperly set execute bit in a directory could return incomplete information about files you otherwise have access to. Any utility that checks queries a directory about it's contents would be affected. In our class we used ls -al as an example.

Extra Bits

We also learned about the maverick bits that control some interesting functions:

SUID This bit reffered to as the Set User ID bit, forces a file to be accessed/run as the owner, with that owner's permissions, regardless of who is accessing the file.

SGID This bit is similar to the one above, except that it forces the file, to take on, and use, the permissions of the file's group, rather than the owner.

T Bit This bit, in files, allows the file to reside in memory, after execution, for the purposes of quicker startup, the next time that file is utlized. For folders, especially those allowing full read and write access, this bit allows users to only create, manipulate and remove only those files that they have created. John Lightsey noted the behavior of "/tmp" as an example of a directory that benefits from use of this bit. This bit is also referred to as the "sticky bit", or the "save text" bit.

Do I look fat?

After we beat the permissions horse to death, we diverted our attention to some simple utilities, that help us find out how much space we're taking up.

du - This utility displays the size of files residing within a directory, and all suddirectories, ultimately concluding with a final sum of all the space taken up. By default it displys n kilobytes, but you can change it to -h to make it human readable, and change the output to megabytes. To only show the grand total, the -s option.

df - This utility displays how much of your hard drive space is being used. It also accepts the -h option, allowing you to see the information in megabytes also.

free - Last, we looked at free, which displays the status of your system memory usage. Unlike, df and du, you must use the -m option to get the information displayed in megabyte format.

To learn more about these utilities, and their other options, check out their manuals, by typing man plus the name of the utility at the command line.

Thanks again, and have fun!

-- AaronEstrada - 04 Oct 2004