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haas:spring2017:sysprog:projects:sci0 [2017/01/26 16:45] – [Execution] wedge | haas:spring2017:sysprog:projects:sci0 [2017/02/14 17:00] (current) – [Submission] wedge | ||
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</ | </ | ||
+ | ====Setting permissions==== | ||
+ | Although we've largely operated without direct attention to it, our data and our access to it very much depends upon the permissions set on them. | ||
+ | You cannot view any source code written without the read permission being set; you cannot save changes unless you have write permission enabled; and you cannot run your compiled programs if the execution permission was not applied. | ||
+ | |||
+ | Different operating systems and different filesystems manifest file permissions differently; | ||
+ | |||
+ | UNIX file permissions are represented as a 3-digit octal (base 8!) value, and each octal value can have the following values: | ||
+ | |||
+ | ^ value ^ description | ||
+ | | 4 | apply read permission to that particular mode | | ||
+ | | 2 | apply write permission to that particular mode | | ||
+ | | 1 | apply execute permission to that particular mode | | ||
+ | | 0 | apply no permissions to that particular mode | | ||
+ | |||
+ | Being an octal value, we can express results ranging from 0-7, and that is precisely how many variations we need to specify all the possible combinations here. | ||
+ | |||
+ | For example, if we wanted read (4) and write (2) permission, we'd add them together... 4+2 is 6; if we wanted read, write, AND execute: 4+2+1 = 7. | ||
+ | |||
+ | There are 3 ' | ||
+ | |||
+ | ^ tier ^ description | ||
+ | | user | permissions applied to the assigned owner of the file | | ||
+ | | group | permissions applied to the assigned group of the file | | ||
+ | | other | permissions applied to anyone else (the world) | ||
+ | |||
+ | More specifically: | ||
+ | |||
+ | ^ ^ user ^ group ^ other | | ||
+ | | read | 0400 | 0040 | 0004 | | ||
+ | | write | 0200 | 0020 | 0002 | | ||
+ | | execute | ||
+ | | none | 0000 | 0000 | 0000 | | ||
+ | |||
+ | To form the octal permission, we figure out what permissions to apply to the user (a combination of read, write, execute, or none), and then for the group, and finally for the world. That is the 3-digit octal value we need. | ||
+ | |||
+ | The problem is that the mode as specified on the command-line will be available as a string (argv[1], an array of characters), | ||
+ | |||
+ | Your program should expect data to be provided as follows: | ||
+ | |||
+ | * argv[0]: program name | ||
+ | * argv[1]: 3-digit permission (as a string) | ||
+ | * argv[2-n]: file to which we want to apply permissions | ||
+ | |||
+ | This can be done rather effectively using logic operations (almost crazy easily). | ||
+ | |||
+ | To get a better handle on this, you may run the following commands when logged into lab46: | ||
+ | |||
+ | <cli> | ||
+ | lab46:~$ ls -l /etc/motd /etc/shadow /bin/ls | ||
+ | -rwxr-xr-x 1 root root | ||
+ | -rw-r--r-- 1 root root 859 Mar 14 12:16 /etc/motd | ||
+ | -rw-r----- 1 root shadow 729 Oct 21 04:55 /etc/shadow | ||
+ | lab46: | ||
+ | </ | ||
+ | |||
+ | Ignoring the leading ' | ||
+ | |||
+ | **/ | ||
=====Program===== | =====Program===== | ||
Line 41: | Line 99: | ||
* the file(s) | * the file(s) | ||
* perform the task (process) | * perform the task (process) | ||
- | * isolate one's digit mathematically, store in a variable (unsigned short int) | + | * as stated, you are not allowed to use any of the **strtol(3)** family |
- | | + | * This isn't to say you cannot use them; you may, you just cannot use them to do any of the conversion work (beyond ASCII to base 10). |
- | | + | * display |
- | * display | + | * if error or usage, make sure you return |
- | * display | + | |
- | * display the resulting number | + | |
- | * display | + | |
- | * because we have not officially learned how to do selection/ | + | |
=====FAQs/ | =====FAQs/ | ||
Line 178: | Line 232: | ||
lab46: | lab46: | ||
</ | </ | ||
- | =====Verification===== | ||
- | One of the tests I will perform for output compliance of your code will involve comparing your program' | ||
- | I will make use of a checksum to verify exactness. | ||
- | You will need to run this from your sof0 project directory with a compiled and operational binary by the name of **sof0**. | ||
- | |||
- | You can check your project by typing in the following at the prompt: | ||
- | |||
- | <cli> | ||
- | lab46: | ||
- | </ | ||
- | |||
- | If all aligns, you will see this: | ||
- | |||
- | <cli> | ||
- | ================================================== | ||
- | = CPROG sof0 project output validation tool = | ||
- | ================================================== | ||
- | sof0 checksum is: 822a47fb2a45845500b6c10878045bd5 | ||
- | your checksum is: 822a47fb2a45845500b6c10878045bd5 | ||
- | ================================================== | ||
- | verification: | ||
- | ================================================== | ||
- | </ | ||
- | |||
- | If something is off, your checksum will not match the sof0 checksum, and verification will instead say " | ||
- | |||
- | <cli> | ||
- | ================================================== | ||
- | = CPROG sof0 project output validation tool = | ||
- | ================================================== | ||
- | sof0 checksum is: 822a47fb2a45845500b6c10878045bd5 | ||
- | your checksum is: 92af264c86823a61529948caaeac53e0 | ||
- | ================================================== | ||
- | verification: | ||
- | ================================================== | ||
- | </ | ||
- | =====Questions / Food for Thought===== | ||
- | These are things I'd like you to contemplate, | ||
- | |||
- | * Why/how does this trick work for 1-digit numbers? | ||
- | * Considering our 1-, 2-, and 3-digit domain restriction for this project, how many candidate values are there for input? | ||
- | * What is the smallest input value? | ||
- | * What is the largest input value? | ||
- | * How many input values are there that end in **5**? | ||
- | * What is the largest square that can be calculated given the project input restrictions? | ||
- | * How many digits is the largest square? | ||
- | * How can knowing how many digits the largest square is help you implement your solution? | ||
=====Submission===== | =====Submission===== | ||
- | To successfully complete this project, the following criteria must be met: | ||
- | |||
- | * Code must compile cleanly (no warnings or errors) | ||
- | * Executed program must display a total of 2 lines, one for input, one for output. | ||
- | * The computed number must be output to STDOUT | ||
- | * Any supporting output must be output to STDERR | ||
- | * Output is formatted in the manner in the sample above | ||
- | * Output must be correct, and match the form given in the sample output above. | ||
- | * Code must be nicely and consistently indented | ||
- | * Code must implement solution using the mental math technique described above | ||
- | * Code must be commented | ||
- | * have a properly filled-out comment banner at the top | ||
- | * have at least 20% of your program consist of **< | ||
- | * Output Formatting (including spacing) of program must conform to the provided output (see above). | ||
- | * Track/ | ||
- | * 25% late penalty per day after deadline | ||
- | * Program is submit in a C source file called **sof0.c** and compiles without warning, note, nor error with gcc on lab46. | ||
- | * Submit a copy of your source code to me using the **submit** tool. | ||
To submit this program to me using the **submit** tool, run the following command at your lab46 prompt: | To submit this program to me using the **submit** tool, run the following command at your lab46 prompt: | ||
<cli> | <cli> | ||
- | $ submit | + | $ submit |
- | Submitting | + | Submitting |
- | -> sof0.c(OK) | + | -> mychmod.c(OK) |
SUCCESSFULLY SUBMITTED | SUCCESSFULLY SUBMITTED | ||
Line 259: | Line 248: | ||
You should get some sort of confirmation indicating successful submission if all went according to plan. If not, check for typos and or locational mismatches. | You should get some sort of confirmation indicating successful submission if all went according to plan. If not, check for typos and or locational mismatches. | ||
- | I'll be looking for the following: | ||
- | |||
- | < | ||
- | 52: | ||
- | *: | ||
- | *:sof0:data stored and calculated in correct and separate variables [4/4] | ||
- | *: | ||
- | *: | ||
- | *: | ||
- | *: | ||
- | *:sof0:no negative compiler messages for sof0.c [4/4] | ||
- | </ |