CSN08112 computer systems bridging

Operating Systems Coursework –

The purpose of this coursework is to introduce you to the functions performed by an operating system and, in particular, to give you experience of the associated command language and the filestore facilities.

On completion of this coursework you will be able to :

• Use the filestore facilities provided by a Linux-based system and particularly, the file attributes and directory structures.
• Use the command language associated with a Linux-based system, including some of the commonly used commands and the commonly encountered structures.
• Appreciate the strategy associated with the testing of systems software, and the need to build robust products.
• Understand and implement ‘best practice’ housekeeping procedures to allow for user/system misuse or mistakes.

SCENARIO

An investigation agency has amassed a large number of important case files on separate flash memory and portable drives. The agency now wish to copy these to permanent server storage.

At present all files for a particular investigative case are stored in individual directories bearing the name of the case.

It is desired to copy the whole directory structure from the portable storage device to permanent file storage as is.

This could be achieved using the simple “cp” command.

E.g. cp $1 $2

cp /mnt/sdb1 ~/my-documents/case_arch

However all of the files have default non-meaningful file names. (e.g.

IMG_0123.jpg, IMG_0002.JPG, Document1.doc, Document2.docx) and it is required that these files are copied with more useful names based on the name of the parent directory.

For example if there is a directory called “clinton” containing the files, IMG_1234.jpg, IMG_4321.JPG and Document1.doc these should be copied to the “clinton” directory on the target drive but with the file names changed to clinton1.jpg, clinton2.JPG and clinton1.doc.

You have been asked to develop a Linux bash shell script which will reliably copy original case directories and files from the flash/portable drive to the permanent storage file space whilst automatically renaming as specified above.

It is also absolutely imperative for the company’s business that no file is ever lost by being omitted or over-written.

The script will need to function with flash/portable drives potentially containing tens of thousands of files and should therefore be reasonably efficient in its operation.

SPECIFICATION

The case custom copy script must be named “cccp” and should be located in the ~/my-applications/bin directory.

It will be used as:

cccp removable_pathname archive_dir_path

Examples:

$ cccp /mnt/sdb1 ~/my-documents/case_arch

$ cccp /mnt/sdb1 ../recordsarc

$ cccp sdb1 /root/records/archive

The first example above would copy all the files from /mnt/sdb1, and any sub-directories within this directory, to the ~/my-documents/case_arch renaming the files in the process

1. The script should be efficient, robust and cope with possible user error.

• If the archive directory does not already exist, the script must create it.

• If the archive directory is not empty then the script should report this as an error and then, as a precaution, terminate.

• If the source directory does not exist, the script should report an error.

• If the user omits either of the two arguments then the script should provide a helpful error message as in:-

“Usage : cccp source_path archive_path”

2. Care must be taken when renaming and copying files so that no files are copied with the same name as one already existing in the target directory, resulting in the loss of the latter.

The script may need to operate on very large collections of files. This means that, even if it is efficient, it still might take a long time to run.

Therefore the script should include checks to make sure that another instance of the script is not already in operation before it starts. If another instance of the script is running then the second one should terminate with an error message.

IMPLEMENTATION

Students should implement the required function as a single script file using “bash” shell script programming.

TESTING

The script functionality should be tested rigorously before submission. The script should work with any appropriate source and destination directories and any reasonable quantity of image and document files.

Example test case files will be provided for help with testing. Students can extract an example set of directories with document and image files from a zipped archive, available from the file repository using a web browser.