Exercises

1. Creat a new userid that you will use instead of root
2. Practice with basic commands
3. Practice with more commands
4. Create a file and use vi to edit the file
5. Searching for more information about your system
6. Using sudo
7. Install the lynx web browser using pkg_add
8. Permissions and files
9. Commands - programs - shell - path
10. Processes and removing them
11. Using /etc/hosts
12. Shutdown and reboot
13. Disk partitions
14. Modules

 
1.) Create a new userid that you will use instead of root: [Top]

First login to your computer if you have not already done so. Login as userid "root" using the password given at the start of class.

Now that you are root you can create a new user account on your machine. You might not use the same machine tomorrow, so do not worry about keeping this account.

First we will have you create an account using the interactive mode of the "adduser" command.

At the prompt type:

adduser

bash-2.05b# adduser
Username: test
Full name: Testing Account
Uid (Leave empty for default): 
Login group [test]:
Login group is test. Invite test into other groups? []: wheel
Login class [default]: 
Shell (sh csh tcsh bash nologin) [sh]: bash
Home directory [/home/test]: 
Use password-based authentication? [yes]: 
Use an empty password? (yes/no) [no]: 
Use a random password? (yes/no) [no]: 
Enter password: yourPassword
Enter password again: yourPassword
Lock out the account after creation? [no]: 
Username   : test
Password   : *****
Full Name  : Testing Account
Uid        : 1002
Class      :
Groups     : test wheel
Home       : /home/test
Shell      : /usr/local/bin/bash
Locked     : no
OK? (yes/no): yes
adduser: INFO: Successfully added (test) to the user database.
Add another user? (yes/no): no
Goodbye!

The faster way to create a user account is to simply use the "pw useradd" facility. For example, to do what we did above you could do by simply typing:

pw useradd username -m -G wheel -s /usr/local/bin/bash
passwd username

Now that you have a new user account log out of the root account (type "logout" or "exit") and login to your computer using your new account.

Sample of this:

# exit
Login: test
Password:
bash-2.05b$

man chpass
man rmuser

2.) Practice with basic commands [Top]

Be careful in this exercise. Running as root means that you can easily damage your system. If you are not sure of a command ask the instructor or helpers before continuing. You should be sure you have logged out as root and logged in using your new userid.

The first command that we are going to use is "man", this is short for "man"ual. Read about each command to see the range of options that exist. Do the following:

man cp
man cd
man ls
man mv
man rm

info cp
info cd
info ls
info mv
info rm

Now we are ready to practice a bit with the commands:

cd /
ls
ls -la
cd /tmp
cd ..
cd tmp

touch text.txt
cp text.txt new.txt
mv text.txt new.txt

cp text.txt /home/userid/.
cd ../home/userid

Now play with the use of the tab key. For example, in /home/userid start to type the first part of the command "cp text.txt text.txt.bak" - then, type:

cp te
cp text.txt te
cp text.txt text.txt.bak

mkdir tmp
mv text.* tmp/.
ls

cd tmp
rm *
cd ..
rmdir tmp

rm -rf tmp

pwd

3.) Practice with more commands [Top]

As you can see from the presentation there are many, many commands that can be used under FreeBSD. If you go to the directories /bin, /usr/bin, /sbin, /usr/sbin, /usr/local/bin, etc. you can see hundreds of files that are programs - many of these are user and system commands. The /bin directory has the critical commands for the operating system. The directory /sbin has, in general, commands that only root runs, or that root can run to make changes (like /sbin/ifconfig).

Please run these commands as logged in as your new user and not root.

To start, do the following:

cd /sbin
ls

man dmesg

4.) Create a file and use vi to edit the file [Top]

Now we are going to open an exmpty file and write something in it. The vi editor works with two modes; one to input data, and the other to give commands. This is fundamental to using vi - You must go in to input mode using a command first, such as i (input) or o (for a newline after the cursor ready for input). To get out of input mode and be able to issue command you must press the ESCape key. Now let's do the following:

cd /root
touch temp.txt
vi temp.txt

Type something like, "VI is great! I think I'll be using vi from now on instead of Microsoft Word."

Press to add lines. Type some more stuff, whatever you like.

Now, remembering the following:

Open: vi fn, vi -r fn, vi + fn, vi +n fn, vi +/pat fn
Close: :w, :w!, :wq, :wq!, :q, :q!
Movement: h,j,k,l, w, W, b, B, :n
Editing: i, o, x, D, dd, yy, p, u
Searching: /pattern, ?pattern, n, N

                        vi Cheat Sheet

Open:  

vi filename             (fn=filename)
vi -r filename          Recover a file from a crashed session
vi + filename           Place the cursor on last line of file.
vi +n filename          Place the cursor on line "n" of file.
vi +/pat filename       Place cursor on first occurrence of "pat"tern

Close:

:w                      Write the file to disk. Don't exit.
:w!                     Write the file to disk even if read/only.
:wq                     Write the file to disk and exit.
:wq!                    Write the file to disk even if read/only and quit.
:q                      Quit the file (only if no changes).
:q!                     Quite the file even if changes.

Movement:

h                       Move 1 space backwards (back/left arrow).
j                       Move down 1 line (down arrow).
k                       Move up 1 line (up arrow).
l                       Move 1 space forwards (forward/right arrow)
w                       Move cursor to start of next word.
W                       Same as "w".
b                       Move cursor to start of previous word.
B                       Same as "b".
:n                      Go to line number "n" in the file.

Editing:

i                       Enter in to input mode.
o                       Add a line below cursor and enter in to input mode.
x                       Delete character (del key in some cases).
D                       Delete line from right of cursor to end of line.
dd                      Delete entire line.
u                       Undo last edit or restore current line.
p                       Put yanked text before the cursor.
yy                      Yank current line.

Searching:

/pattern               Search for "pattern" in the file going forwards.
?pattern               Search for "pattern" in the file going backwards.
n                      Find the next occurrence of pattern found forwards.
N                      Find next occurrence of patter found backwards.

Now press "/" and type a word that is in your document, then press . What happens?

Do the same, but press the "?" key at first. Use ESCape to start in command again again if necessary.

To save your file press the ":" key and next type "w" and enter . .

To exit and save do:

:wq

:q!

5.) Searching for more information about your system [Top]

If you want to see the contents of a file there are three typical ways to do this:

cat
less
more

Test this using the three commands using them with an informational file like:

cd /etc
cat motd
more services
less services (you can exit with "q")

man fstab
man rc.conf
man termcap

6.) Using sudo [Top]

When you created your test user you placed it in the wheel group. This means you can use the su (Substitute User identity) command to become another user without having to login and logout of your session, and you can use the sudo command to execute privileged commands from your standard user account. Let's practice this a bit. First from your standard user account use su to become root:

su - root

Now let's drop back to your standard user account and try to do something that requires privileges:

exit

less /etc/master.passwd

sudo less /etc/master.passwd

So, as root:

su -

The sudoers file is quite powerful. You can create complex entries to give specific users, groups, etc. access to specific sets of commands. In addition, you can create aliases for command names, and then you can use these aliases when specifying what a user or group is allowed to do. This is very useful if you wish to give one set of users "network administrative" access and, perhaps, another set "database administrative" access. Perhaps one of these users suddenly needs both - using aliases will make this much easier.

You should take a moment to see what's possible by reading:

man sudoers

For our case we are simply going to add an entry in to the file /usr/local/etc/sudoers that will allow your userid to execute all system commands (there are a few exceptions). To do this you must use the "visudo" facility to safely edit this file:

visudo

Now scroll through the file until you find the entry that reads:

wheel = ALL (ALL)

youruserid = ALL (ALL)

sudo less /etc/master.passwd

Try doing "sudo less /etc/master.passwd" again. What happened? You were not prompted for a password again. Once you run successfully sudo during a login session, then you don't need to enter in a password the next time you use the command. Naturally this means you should really log out any user session that has sudo privileges if you leave a terminal unattended.

If you have a server with multiple users who need to do system administration of some kind, but you don't want to give all these users full access to your system, then be sure that you read "man sudoers" carefully so that you can take advantage of this facility to restrict and give access appropriately.

7.) Install the lynx web browser using pkg_add [Top]

Now we are going to add the lynx text-based web browser using the pkg_add command and our local network server.

First, you can see if lynx is already installed on your system. Use the pkg_info command to do this. To get an idea of what packages are installed and what the default pkg_info output looks like type:

pkg_info | more

Now to check for just the lynx package type:

pkg_info | grep lynx

pkg_delete lynx-ssl-2.8.5

pkg_info | grep lynx

Now to install lynx directly from our noc box in the classroom you can simply type:

pkg_add ftp://noc/home/ftp/pub/pkgs/lynx-ssl-2.8.5.tbz

pkg_info | grep lynx

Test lynx out by typing:

lynx noc
q (to exit lynx)

8.) Permissions and files* [Top]

*Reference: Shah, Steve, "Linux Administration: A Beginner's Guide", 2nd. ed., Osborne press, New York, NY.

If you look at files in a directory using "ls -al" you will see the permissions for each file and directories. Here is an example:

drwxrwxr-x    3 hervey   hervey       4096 Feb 25 09:49 directory
-rwxr--r--   12 hervey   hervey       4096 Feb 16 05:02 file

The left column is important. You can view it like this:

Type User    Group World Links  owner  group  size   date   hour  name
d    rwx     rwx   r-x   3      hervey hervey 4096   Feb 25 09:49 directory
-    rwx     r     r     12     hervey hervey 4096   Feb 16 05:02 file

So, the directory has r (read), w (write), x (execute) access for the user and group. For world it has r (read) and x (execute) access. The file has read/write/execute access for the world and read only access for everyone else (group and world).

To change permissions you use the "chmod" command. chmod uses a base eight (octal) system to configure permsissions. Or, you can use an alternate form to specify permissions by column (user/group/world) at a time.

Permissions have values like this:

Letter  Permission   Value

R       read         4
W       write        2
X       execute      1

Thus you can give permissions to a file using the sum of the values for each permssion you wish to give for each column. Here is an example:

Letter  Permission                   Value

---     none                         0
r--     read only                    4
rw-     read and write               6
rwx     read, write, and execute     7
r-x     read and execute             5
--x     Execute                      1

This is just one column. Thus, to give all the combinations you have a table like this:

Permissions  Numeric      Description
             equivalent  

-rw-------   600          Owner has read & execute permission.
-rw-r--r--   644          Owner has read & execute.
                          Group and world has read permission.
-rw-rw-rw-   666          Everyone (owner, group, world) has read & write
                          permission (dangerous?)
-rwx------   700          Onwer has read, write, & execute permission.
-rwxr-xr-x   755          Owner has read, write, & execute permission.
                          Rest of the world has read & execute permission
                          (typical for web pages or 644).
-rwxrwxrwx   777          Everyone has full access (read, write, execute).
-rwx--x--x   711          Owner has read, write, execute permission.
                          Group and world have execute permission.
drwx------   700          Owner only has access to this directory.
                          Directories require execute permission to access.
drwxr-xr-x   755          Owner has full access to directory. Everyone else
                          can see the directory.
drwx--x--x   711          Everyone can list files in the directory, but group
                          and world need to know a filename to do this. 

Now lets practice changing permissions to see how this really works. As a normal user (i.e. don't login as root) do the following:

cd (what does the "cd" command do when you do this?)
echo "test file" > read.txt
chmod 444 read.txt

chmod 744 read.txt

chmod u+w read.txt

chmod u+r, chmod u+w, chmod u+x
chmod g+r, chmod g+w, chmod g+x
chmod a+r, chmod a+w, chmod a+x

Note that "a+r" is for world access. The "a" is for "all", "u" is for "user", and "g" is for "group".

Now, change the file so that the owner cannot read it, but they can write to the file...

chmod u-r read.txt

chmod 344 read.txt

Finally, there is a concept that when you execute a file you normally execute it using the permissions of the user who does this. Por example, if the user "carla" types "netstat", the netstat programs runs with their privileges. But, if you want netstat to always run with the permissions of the owner or of the group of the netstat program, then you can configure the "SetUID" or "SetGID" bit. You can do this using chmod. However, remember that this can be a bad idea from the viewpoint of security...

To do this add a "4" to the chmod octal to set the SetUID, or a "2" to set the SetGID bit.

As an example, you could do:

chmod 4755 /usr/bin/netstat

And, to set the SetGID bit it would be:

chmod 2755 /usr/bin/netstat

-rwsr-xr-x    1 root     kmem       106344 Feb 23  16:42 /usr/bin/netstat

Note the "s" en the owner column.

And, after you issue the command "sudo chmod 2755 /usr/bin/nestat" the permissions look like this:

-rwxr-sr-x    1 root     kmem       106344 Feb 23  16:42 /usr/bin/netstat

Not that we would necessarily recommend that you do this... But, it is good to understand this concept. So, if you did this, then to unset the SetGID and/or the SetUID bit you can issue chmod like this:

chmod 0755 /usr/bin/netstat

-rwxr-xr-x    1 root     kmem       106344 Feb 23  16:42 /usr/bin/netstat

9.) Commands - programs - shell - path [Top]

For this exercise we want you to run as a user other than root. So, if you are root do this:

su - user

When you type a command or the name of a program the system looks for something with that name using in the directories specified in your PATH environmental variable. Or, if the command is a built-in shell program (such as "cd", see "man builtin"), then it will execute the command without needing to use the PATH variable. To see your what your PATH is set to, do this:

printenv PATH

To see how this works let's create a shell script that will run a simple command, but which resides in a directory outside your PATH statement ("user" here is the name of your own userid).

cd /home/user
mkdir scripts
cd scripts
vi hello.sh

#!/bin/sh
#
 
echo hello

Remember to save and exit the file (:wq). And, to ensure that you can execute the file use the command:

chmod u+x hello.sh

Now we are going to add the /home/user/scripts directory to our login profile PATH statement.

cd /home/user
vi .profile

PATH=/sbin:/bin:/usr/sbin:....:$HOME/bin; export PATH

and change it so that at the end of the PATH statement you add:

PATH=/sbin:/bin:/usr/sbin:....$HOME/bin:$HOME/scripts; export PATH

Save the file and now do the following:

hello.sh
. .profile
hello.sh

You may have noticed the "$HOME/bin" item in the PATH. As you can see FreeBSD has the concept that you may wish to have your own personal bin directory for executables, so normally the "hello.sh" script might reside in /home/user/bin, but for purposes of this exercise we used /home/user/scripts.

Finally, if you want to change something like the PATH for everyone you can do this in two ways. One, you could update /etc/profile with a new PATH statement. This means that everyone on your system will see this change as soon as they login the next time. Or, you can change /usr/share/skel/dot.profile so that all new accounts have the new PATH, but previous users will not see this change. In both cases changes like this should not be done lightly. When setting up a server with many users you will probably want to think about what directories your users need to have in the PATH from the beginning and update /usr/share/skel/dot.profile before creating initial user accounts.

In addition, you can run the "hello.sh" script by typing "/home/user/scripts/hello.sh" at any time.

To finish up we are going to change how the "rm" command runs to make it "safer" (in my opinion). Here are the steps:

vi /home/user/.profile

alias rm='rm -i';

Now exit and save the file (:wq). After that type:

touch temp.txt
rm temp.txt
. .profile
touch temp.txt
rm temp.txt

10.) Processes and removing them [Top]

If you would like to see what is running on your system, then you use the "ps" command (ProceSs). For example, to see everything running on your system for all users, and even items running that are detached type:

ps -aux

ps -aux | grep mozilla

kill nnnn

kill -9 nnnn

If you see something running that you do not want to have run each time you boot, then you can, generally, edit /etc/rc.conf and override the setting that starts this service (see /etc/defaults/rc.conf). You can stop the service immediately by using the "kill" command. If you are testing a configuration file for a known running service (say the Apache web server) you can, often, tell the service to restart reloading the configuration file, but to reload using the same parameters it originally used to start. This can be very useful if the service requires a complex set of parameters to restart. The command to do this is:

kill HUP nnnn

Finally, some programs spawn many processes when running. Web browsers are an example of this. It can be time-consuming to kill each process one-by-one until you have completely shut down the program. An alternate command is "killall" which will kill processes by name. Naturally you have to be a bit careful with this as you could shutdown something unexpectedly, but if you have 20 processes all called "Mozilla" that you want to stop, then you can simply type:

killall mozilla

11.) Using /etc/hosts [Top]

If you look at /etc/resolv.conf you will see the default search domain for your machine and the dns server that you are to use to do name lookups. Naturally this information has either been hardcoded in to your /etc/rc.conf file for the network interface(s) on your box, or you have a line that reads something like this in /etc/rc.conf:

ifconfig_wi0="DHCP"

Even so, your box needs to have a backup in case you do not have network connectivty, don't use a network, or your dns service goes down. Network applications want to know the default name for 127.0.0.1. In most cases you will simply place localhost.localdomain in /etc/hosts for this IP address, and that will be all you will need.

In some cases you might have a private network without a name server where you hard code your IP to name associations. Naturally, as you well know, this does not scale. In any case your /etc/hosts files should have at least the following line:

127.0.0.1               localhost localhost.localdomain

In addition, we are likely to use this file for convenience's sake during this workshop (or we could set up a dhcp server...). At this point you should edit the file /etc/hosts and you should put in the IP address and the name "noc" for our classroom server. For instance, if we are using a private network like 192.168.1.0 and our noc box is 192.168.1.254 (maybe it's a gateway box as well...), you would add a line to /etc/hosts and enter in something like:

192.168.1.254    noc               noc.ws.domain

lynx noc

Finally, you can change the order in which name lookups take place under FreeBSD. You do this by creating and editing the file /etc/nsswitch.conf (name service switch configuration file). You can find a sample of this file here in /usr/compat/linux/etc/nsswitch.conf. In most cases you should not make changes to this file. However, if you run a service like Samba, then you may need to make changes to the line with the "hosts" statement. By default name lookups are done first by checking /etc/hosts, then by resolving to the nameserver address in /etc/resolv.conf.

12.) Shutdown and reboot [Top]

For this exercise you need to be root. It is better to close open files and programs (for example Mozilla, vi, etc.), but it is not necessary. Before continuing read the man pages for shutdown, init, halt, and reboot (you'll see they are all connected):

man shutdown
man init
man reboot
man halt

shutdown -r now

halt

init 0

init 6

13.) Disk partitions [Top]

First, make sure you are logged in as your user and not as root.

Now in a terminal lets look at the partitions. Type:

df
df -h

swapinfo

If you want to see more detailed information about your disk slices you can use the "fdisk" command. As a general user you are not allowed to run this program, so you must use sudo. Try this by typing:

sudo fdisk

If you are interested in how much space files are taking up in a directory or a group of directory you can use the "du" command. Try it out by typing:

du

du -h

14.) Modules [Top]

This is short, but just so that you know you can manipulate dynamically loaded modules in FreeBSD. To see what is loaded type:

kldstat

In our case there is probably nothing you can unload, but this is good thing to understand. You can type "kld" and tab to see the various kld commands. Then type "man kldxxxx" to read about the details of using each command. That is, look at these commands in more detail like this:

man kldconfig

man kldload

man kldstat

man kldunload

man kldxref