answers to lab 4

Q: 1. Create a file called "exercise04answers.txt" A: e.g.

touch exercise04answers.txt

Q: 2. At the top of the file, use the label as defined before. A: as before

Q: 3. Put on a line the word "lab" by itself, then work on lab exercises 1-5 below. List all the relevant commands and arguments that you had to use in the lab exercises. Put in comments to show why you did something (this can help your mark even if you did something wrong). A: in sequence

In my directory on the course linux server (my username is "gj"), is a directory called "public_html/dropbox". In this location, create a directory the name of which is your studentid. Set the permissions on this directory to only allow yourself all permissions (i.e. make sure that nobody else on the system can get into this directory). Create a link called "mysyslog" into your directory, link it to the file called "syslog" in "public_html/". Make sure you can read its contents. From here on, all lab exercises should take place in the directory you have just created (i.e. any new files you create have to go in there).
```
# go to the directory, so I don't have to type so much
cd ~gj/public_html/dropbox/

# create directory, where my studentid is 01234567890
mkdir 01234567890

# set the permissions as indicated with chmod
chmod 700 01234567890

#link the file
ln ../syslog 01234567890/mysyslog

#go to the directory
cd 01234567890
```

From mysyslog, select all those lines that have to do with firewall rules, example:
Feb 13 20:20:33 idallen-home1 kernel: Shorewall:net2all:DROP:IN=eth0 OUT= MAC=00:80:c8:4b:b7:75:00:04:e2:50:08:96:08:00 SRC=4.164.5.254 DST=192.168.9.198 LEN=908 TOS=0x00 PREC=0x00 TTL=117 ID=17592 PROTO=UDP SPT=13111 DPT=1026 LEN=888
But do not select any other lines. Put these lines in a file called firewall.log You may not use an editor or cut and paste.

# we look for "Shorewall"
grep Shorewall mysyslog > firewall.log

How many lines are there in firewall.log? How many different source IP addresses are there in firewall.log? How many different destination IP addresses? How many different source ports? How many different destination ports? Find an efficient way to get these numbers (counting on your fingers is not efficient!).

# How many lines
wc -l firewall.log

# How many different source IP addresses
cut -d' ' -f9 firewall.log | sort -u | wc -l

# How many different destinateion IP addresses
cut -d' ' -f10 firewall.log | sort -u | wc -l

# How many different source ports
cut -d'=' -f13 firewall.log | sort -u | wc -l

# How many different destination ports
cut -d'=' -f14 firewall.log | sort -u | wc -l

Create a file called "partgroup", the contents of which are selected from the GIDs from the first 20 lines of the password file. Make sure the list is sorted in reverse numerical order, and remove the highest and lowest number. You may not use an editor, or copy and paste to create this file. (Build your command pipeline!) Explain what every part of the pipeline does (or is supposed to do).
```
# first 20 lines, GID only (fourth field), sort reverse numeric,
# remove the last line, remove the first line, redirect to "partgroup"
head -20 /etc/passwd | cut -d: -f4 | sort -rn | head -19 | tail -18 > partgroup
```
List all the umask setting so that when you create a file, you end up with permissions r---w-rw-. List all the umask settings so that when you create a directory, you end up with permissions r-x-wxrw-.
```
240, 241, 250, 340, 341, 350, 351
and
241
```

Q: 4. Put on a line the word "book3" by itself, then answer questions 1-6, 8-11 and 14, from the book, chapter 3, pages 72-73. A: in sequence

1.
```
w
```
and
```
who
```
2.
```
mesg n
```
to keep your screen from being "messed up"
3. after
```
cp to_do done
```
the file done and the file to_do have the same contents, and the original contents of the file done are gone, after
```
mv to_do done
```
the file done has the contents that to_do used to have, and the file to_do is gone.
4.
```
apropos edit
```
or
```
man -k edit
```

grep 'Ace Electronics' phone

sort phone

unic phone

sort -u phone

sort phone | unic

6. diff tells you the files are different, but it doesn't show you how they differ. Normally diff shows the lines you have to insert, delete or replace, but you don't have "lines" in binary files.
8. in that case which will not show you the pathname of the file in the current directory as an option.
9. yes. use 'whereis command' to find out different locations for standard utilities.

10.

file /usr/bin/* | cut -d: -f2 > tempfile
# remove leading whitespace with vi
vi tempfile
# sort -u tempfile | wc -l

11.
```
head status.report
```
```
tail status.report
```

14.

zgrep 'Ace Electronics' phone.gz

gzip -cd phone.gz | grep 'Ace Electronics'

gunzip phone.gz; grep 'Ace Electronics'

zcat phone.gz | grep 'Ace Electronics

These same approaches work for all the other answers for question 5.

Q: 5. Put on a line the word "book5" by itself, then answer questions 2-4, 6-10, 12, 16, chapter 5, pages 134-136. A: in sequence

2.
```
sort list | lpr
```
3. PID is the process identifier (number). They allow you to identify the processes that you are running by a unique number. ps displays the PID of the commands you are running.
4.a
```
ls sec*
```
4.b
```
ls s*[123]
```
4.c
```
ls i*
```
4.d
```
ls *[13]
```
6.a
```
sort phone_list > numbers
```
6.b
```
cat permdemos.c | tr '[{}]' '(())'
```
6.c
```
cat part1 part2 > book
```
7.a grep and cut
7.b tr
8.a
```
grep root < /etc/passwd > tempfile
```
8.b
```
grep root < /etc/passwd
```
8.c
```
grep root /etc/passwd > tempfile
```

8.d

cat /etc/passwd | grep root | cat > tempfile

grep is a filter in a, b and d
9. the arguments to the rm command contain abc twice, so when rm gets to its second argument, it complains (because that file has already been removed). After this command sequence, ls will give no output.
10.
```
cat does-not-exist > newfile
```
, where the file does-not-exist does not exist. Cat generates an error message and no standard output.

12.a

cp /dev/null filename

cat > filename
^D

cat does-not-exist > filename

12.b you can have write permissions to a file, but not have write permissions in the directory that that file resides in.
16. (after the type is fixed) the shell creates (and empties) the file "answers.0102" and prepares standard output for the command that it is about to execute to be redirected into this, then it opens "answers" as input for the command command that it is about to execute, then it executes the command cat.
Q: 6. Put on a line the word "bonus" by itself, then answer lab question 6 below.
- 6. Bonus points: there are two mistakes in the book on page 605. Identify the mistakes. What should the text really say to be correct?
  1. Only Superuser can set the sticky bit
  2. it can be used only with u
  Sets the sticky bit, and it can be used with both o, a, or by itself with the + or = sign.
Q: 7. Submit using the datsubmit command
A: datsubmit 04 exercise04answers.txt