G1): Do A Lot With Files And Directories¶

Precondition: Logged-In To Remote/Exam Computer ¶

Logged in to remote computer

$ ssh -p 2020 firstname.lastname@jfasch.bounceme.net

Danger

The exam must be done on the remote computer

Take care to not accidentally execute the following steps on your local machine!

$ tree ~/exam-01/
~/exam-01/
├── credentials
├── private-place
└── public-place

In the directory ~/exam-01/credentials, create a bunch of files as follows:

Filename	Content
`name`	Your UNIX username and user ID (UID), one line each; for example $ cat ~/exam-01/credentials/name joerg.faschingbauer 1020
`primary-group`	The name and group ID (GID) of your primary group, one line each; for example $ cat ~/exam-01/credentials/primary-group joerg.faschingbauer 1020
`supplementary-groups`	The name and ID of your supplementary groups, one line each; for example $ cat ~/exam-01/credentials/supplementary-groups joerg.faschingbauer 1020 ece20 1021

Hint

See Login? What Is That? for how to find out who you are.

Hint

You use the >> operator to append a line to an existing file (or to create that file if it doesn’t exist):

$ echo 8020 Graz >> somefile.txt

Tune the permissions of the ~/exam-01/public-place directory in a way that

You can
- look and cd into it
- create files in it
- remove files from it
Your fellow members of the ece20 group
- can look and cd into it (and thus see its contents)
- can not create files in it
- can not remove files from it
Nobody else has any permissions in that directory

Hint

You use the -d option (together with -l of course) to the ls command to view the permissions of the directory itself, not its contents.

For example, this shows the initial - not-yet-tuned - permissions of the directory:

$ pwd
/home/joerg.faschingbauer/exam-01
$ ls -ld public-place/
drwxr-xr-x 2 joerg.faschingbauer joerg.faschingbauer 4096 Mar 24 07:00 public-place/

Tune the permissions of the ~/exam-01/private-place directory in a way that

Create a file completely-open.txt in ~/exam-01/public-place in a way that
- It contains the phrase “Hello teacher”
```
$ cat ~/exam-01/public-place/completely-open.txt
Hello teacher
```
- You can modify/write that file
- Your fellow members of ece20 can only read it, but not write it
Create another file completely-open-removable.yesno in ~/exam-01/public-place that contains either yes or no, answering the following question:

Would any member of the ece20 group be able to remove completely-open.txt?

Goal

Transfer what you created (i.e. the entire contents of the remote ~/exam-01 directory) to your local machine.
Use the scp command for this task
But read on! Do not start!!

Think

What would be the command to do this?
Note that we were extremely picky to restrict permissions in most parts of the tree. How would you preserve those valuable permissions across the remote copy?

(Hint: read the scp manual page, and find out about the -p option.)
Create a file backup-command.sh in ~/exam-01/ containing that command.
Make this file executable for all users, but otherwise preserve its default permissions that it had initially.
Finally, execute the scp command on your local machine