Exercises
Note 2: If you install software, update your environment as root and the change is not immediately available try typing rehash at the root shell prompt. This is only necessary when running a C shell (e.g., like /bin/csh).
2.) Use pw to 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 in class.
Now that you are root you can create a new user account on your machine. If more than one person is using your machine, then be sure that you create an account for each and every person.
To create or remove a user account you should use the "pw" command. To get a feel for the power and complexity of this command take a look at its man pages (we'll practice man some more later):
# man pw
So, first pick a username that you want to use. For example, use your first name, last name, a combination of both, or whatever you prefer. For purposes of this example we use username. So, to add a new user to your system type:
# pw useradd username -m -s /usr/local/bin/bash
This creates the user username. The "-m" says add a new home directory of /usr/home/username and copies files from /usr/share/skel to the new user's home directory. The default shell "bash" will be used. Note that at this point the bash shell has not been installed on your machine. We'll be doing this in the upcoming exercises.
Next you need to set the password for the new userid, otherwise you won't be able to use the account properly. To do this one uses the passwd command. Change your new user's password using the command:
# passwd username
You will be prompted to enter in a new password, then to enter it again to verify. You need to pick a secure password. Note, as root you are allowed to pick any password you want, but you need to pick a secure password for your new account. Here are some quick guidelines to picking a secure password:
To use your new account you can logout from your current session and log in with the new username and password.
2.) Practice with basic filesystem commands [Top]
Be careful in this exercise. Running as root (the Unix administrative account) means that you can easily damage your system, so we ask that you log out of your root account and log in as your own user account instead.
To logout, type
# exit
If you are unsure of how to proceed ask your instructor or assistants for help before continuing.
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.
Many of the basic commands we'll be practicing are built in as part of your shell environment (that is you won't find a binary/program file for cd). To read about commands like cp, cd, ls, mv, rm in more detail you can just type:
$ man builtin
And, for a command like ls you can type:
$ man ls
And, even for a built-in command you can just type "man commandName", or something like:
$ man cd
and this will open the "builtin" man page for you.
If you have problems exiting from "man" press the "q" key. Also, you can use the keyboard arrows to move around in the descriptions.
As we move around directories an extremely useful command is pwd, which return the working directory name you are in. So, if you get lost just type:
$ pwd
We'll do this from time to time as we use directory commands.
Simplified Map of Unix Directory Tree
/ ("root directory")
/etc (contains configuration files)
/etc/rc.d (contains system startup scripts)
/root (user root's home directory)
/tmp (place to store TeMPorary files)
/usr (contains the majority of user utilities, applications, home directories)
/usr/home (home directories for users on the system*)
/usr/local/etc (contains third-party configuration files and startup scripts*)
/var (multi-purpose log, temporary, transient, and spool files location)
*Different from Linux
For details on the (almost) complete directory tree under Unix/Lunx type "man hier"
Command Glossary
cd Change Directory ls LiSt files mkdir MaKe DIRectory mv MoVe files pwd Print Working Directory rm ReMove files rmdir ReMove DIRectory touch Update date on file/Create new empty file if none exists
Note: There are some special files on UNIX, which are '.' and '..':
'.' - "this" directory (the one you are "in" as reported by the pwd command
'..' - the parent directory, i.e.: the one above
Now we are ready to practice a bit with the commands:
$ cd /
$ pwd
$ ls
$ ls -la
$ cd /tmp
$ cd ..
$ pwd
$ cd tmp
What's going on here? If you don't understand, ask.
$ cd (take you back to your home directory)
$ pwd
$ touch text.txt
$ cp text.txt new.txt
$ mv text.txt new.txt
What's happening now? If prompted to overwrite, respond
"y". Note that "username" is the name of the user account you created in
the first exercise.
Now watch what happens if you try to copy a file on itself.
$ cp new.txt /home/username/.
$ cd ../../home/username
$ cd (to return to our home directory)
$ cp new.txt new.txt.bak
The tab key makes life much easier. Now type:
$ cd
$ mkdir tmp
$ mv new.* tmp/.
$ ls
Finally, we are going to remove the directory that contains the two archives.
$ cd tmp
$ rm *
$ cd ..
$ rmdir tmp
You can force this using a command like this:
$ rm -rf tmp
The use of "rm -rf" is very dangerous!, and,
naturally, very useful. For example, if you are "root" and you type "rm
-rf /*" this would be the end of your server. This commands says
"remove, forcibly and recursively, everything" - Or, if you start in
the root directory (/), remove all files and directories without asking on the entire server. If you want to use "rm -rf *" always take a deep breath and check where you are first (really, do this!):
$ pwd
First this says in what directory you are. If you are mistaken, then you have the opportunity to not remove files that you might really need.
3.) Getting help using manpages, docs, and the FreeBSD Handbook [Top]
Now that you have FreeBSD up and running you probably want to have a way to figure out how to use it when there are no instructors around, or other FreeBSD-knowledgeable people. First and foremost, make it a habit to read the man pages (MANual pages) for the commands that you use. You might be surprised at some of the things these commands can do! In any case, as you have seen, when in doubt about what a command does, or how it works simply type:
$ man command
Optionally, you might find some additional information for some commands typing:
$ info command
And, to get information about both these commands type:
After this there is a large amount of documenation available to you in serveral ways. For instance, if you look in:$ man man
$ info info
/usr/share/doc
you will find multiple FreeBSD articles in various languages
available to you. In addition, the FreeBSD Handbook is available here
under /usr/share/doc/handblook. If you wanted to start reading the
FreeBSD Handbook from your local hard drive you could use a web
browser on the file /usr/share/doc/handbook/index.html. In URL format in your web browser this looks like:
Note: we are likely not using a graphical interface at this time.
file:///usr/share/doc/handbook/index.html
There is, also, a FreeBSD FAQ file you can look at here:
file:///usr/share/doc/faq/index.html
After this, have a look at some of the available articles by doing the following in a terminal window.
Finally, there are several papers available as well. Try:$ cd /usr/share/doc/en/articles
$ ls
$ ls /usr/share/doc/papers
If you have a network connection, then you can go to http://www.freebsd.org/docs.html
for even more information. Become accustomed to the idea of using man
to get specific information about commands, and then using these
additional resources to get an overview of entire sub-systems of the
FreeBSD operating system. If you want to read the FreeBSD Handbook online it is available here
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/index.html. If you want to understand FreeBSD concepts in more depth,
then the FreeBSD Handbook is really where you should begin.
4.) General job control (ctrl-c) [Top]
For this exercise you need to be logged in as root.
When you wish to stop an active process in your shell you can use the keyboard combination "ctrl-c". If this does not work, then you may want to try "ctrl-z". The ctrl-z sequence will suspend the process allowing you to place it in the background using the bg (BackGround) command. This is a bit more complex, but let's practice using ctrl-c right now:
# cd /
# ls -R (starts to recursively show contents of all directories on your system)
press CTRL-C (aborts the output)
In addition, when you type "man command" you can press the "q" key to exit from viewing the man pages. The same goes for "less" as well.
Now let's start a process in your shell to requires you to use ctrl-c to end the process:
# tail -f /var/log/messages
In this example you are viewing the end of the main log message for your system with data appended to the output as the file grows. That is, if a message is generated and placed at the end of the log file you will see this message interactively appear on the screen. This is a very useful tool when you are trying to debug problems on your system. You can open one terminal window (as root, or with an account that can run privileged commands), type "tail -f /var/log/messages", start a process in another terminal window and then view the end results in the window where the tail command is running.
Now to end the "tail -f" process press ctrl-c to abort the output. In this case "q" or "ESC" will not work. You need to know about ctrl-c to do this.
6.) Viewing file contents [Top]
If you want to see the contents of a file there are three typical ways to do this:
Each of these commands has it's own features:$ cat
$ less
$ more
Test this using the three commands using them with an informational file like:
$ cd /etc
$ cat motd
$ more services (you can exit with "q")
$ less services (you can exit with "q")
Try looking at some more files, for instance, fstab,
rc.conf, termcap, etc. If you don't understand what you are looking at,
then use the "man" command. For example, type:
$ man fstab
$ man rc.conf
$ man termcap
Finally, there is one other useful command for looking inside files. This command is tail.
We will need to run this this as the root user. So, do this:
Now type:$ logout
login: root
password: <given in class>
# tail /var/log/messages
This will show you the last few lines of your main logfile on your system. This can be really useful if you just want to see what the last thing written to a file was. Your file /var/log/messages will get very large over time, so if you used cat, less, or more to view this file for new messages this could become very time-consuming. Now, even more fun is to do the following:
# tail -f /var/log/messages
Now press CTRL-ALT-F3 to go to one of your virtual terminals. Login as root on this terminal. Now go back to your original terminal where you typed the command tail -f /var/log/messages by pressing ALT-F1. You should see a message on the screen saying that root just logged in. The "-f" option means, "output appended data as the file grows" - or, you can watch each new item as it's written to the end of a file. This is incredibly useful when you are trying to debug problems and you need to see what happens in your logfiles in real time.
Don't forget to log out of your other terminal window.
If you have any questions ask the instructor or one of the class helpers.
7.) File and directory permissions* [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
In spite of the fact that the file does not have write
permission for the owner, the owner can still change the file's
permissions so that they can make it possible to write to it:
$ chmod 744 read.txt
Or, you can do this by using this form of chmod:
$ chmod u+w read.txt
The forms of chmod, to add permissions, if you don't use octal numbers are:
$ 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
Or, you can do something like:
$ chmod 344 read.txt
You probably noticed that you can use the "-" (minus) sign to remove permissions from a file.
A UNIX Permissions "Gotcha"
If a directory has the World or Group write flag set, and contains a file that is only writeable by the owner, then a member of either the Group or World (everyone) can still make changes to the file. Here's an example of how (become root to do this):
You will receive the following prompt:# mkdir /tmp/test
# echo "example text" > /tmp/test/example.txt
# chmod 644 /tmp/test/example.txt
# chmod a+w /tmp/test
# su - userid
$ cp /tmp/test/example.txt .
$ echo "add more text to file" >> example.txt
$ mv example.txt /tmp/test/example.txt
If you press "y" and ENTER, then your version of the file will now overwrite the read only version of the file owned by root in the /tmp/test directory. This is because write permission has been enabled for World on the /tmp/test directory. Thus, you have permission to mv (i.e. rename) a file of the same name to this directory. This result may seem surprising. If you do:override rw-r--r-- root/wheel for /tmp/test/example.txt? (y/n [n])
$ ls -al /tmp/test
You will see that your userid now owns the file. The root user no longer owns the file. So, using this trick is pretty obvious, unless, of course, you set things back to the way they were using the chown command.
8.) Disk partitions: how to view your disk [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
What difference did you see between "df" and "df -h". How
can you see what your swap contains (note it was not listed using
"df")? Use this:
$ 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:
$ fdisk
Be careful with fdisk as you can remove slices, partitions, etc.
If you are interested in how much space files are taking up in a directory or a group of directories you can use the "du" command. Try it out by typing:
As usual you can get more information by typing "man du".$ du
$ du -h
Now that you've seen these methods for viewing disk information, you should be able to understand the output of the disklabel command a little better. The disklabel command is really the proper way to view the status of partitions in your FreeBSD slice at it will show you all your FreeBSD slice information no matter if a partition is mounted or not. In some cases this is critical if you are trying to troubleshoot problems and not all partitions have mounted. In order to use disklabel you need to be root.
So, if FreeBSD resides on the slice /dev/ad0s1 on your disk, then to see disk information you type:
# disklabel /dev/ad0s1
(Note, we are assuming we are using IDE drives) If we are This shows you output along these lines (will be different for this workshop):
As you can see it includes the "c" partition and "b" or the "swap" partition as well as filetypes.# /dev/ad0s1: 8 partitions: # size offset fstype [fsize bsize bps/cpg] a: 409600 0 4.2BSD 2048 16384 25608 b: 1433600 409600 swap c: 8385930 0 unused 0 0 # "raw" part, don't edit d: 1843200 1843200 4.2BSD 2048 16384 28552 e: 3072000 3686400 4.2BSD 2048 16384 28552 f: 1627530 6758400 4.2BSD 2048 16384 28552
9.) Create a file and use vi to edit the file [Top]
We are going to open an empty file and write something in it. You can be root or a regular user for this exercise. It's better to not be logged in as root whenever possible (hint!).
The vi editor uses "modes"
This is a critical point. The vi editor has two modes. These are:
Now let's do the following:
$ cd /home/username
$ touch temp.txt
$ vi temp.txt
Now you are in vi. Press the "i" key to switch to input mode.
Type something like, "VI is great! I think I'll be using vi from now on instead of Microsoft Word."
Press ENTER to add lines. Type some more stuff, whatever you like.
Here is a short list of vi commands:
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
OK, let's save the file that you are in. To do this do:
Press the ESCape key to get in to command mode
Press ":" to get ready to issue a file command
Type "w" and press ENTER to save your file.
Press ":" to get back to the prompt to issue a file command
Press "q" to quite the file
Instead of the multiple steps you could have type ":wq" to write and quite at the same time. If you need to quit a file without saving it after you've made changes, then you press :q!. For many people this is the most important command to remember in vi :-).
Below is a more complete vi cheat sheet. In addition you will be receive a vi summary book as part of the book package for this workshop.
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: A Move to end of line, change to insert mode. 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. Copy/Cut and Paste nyyp Copy n lines to buffer, paste below cursor nyyP Copy n lines to buffer, paste above cursor nddp Cut n lines and copy to buffer, paste below cursor nddP Cut n lines and copy to buffer, paste above cursorNow let's copy a large file to your home directory so that you can play around with some more vi commands. We'll copy over your /etc/defaults/rc.conf file for this exercise. To do this we do:
Play with moving around. Move your cursor to a line with text and see what happens when you go in to command mode (ESCape) and use "w" or "W" or "b" or "B" - remember, to get in to command mode press the ESCape key.$ cd
$ cp /etc/defaults/rc.conf .Now let's edit this file. To do this type:$ vi rc.conf
Now press "/" and type a word that is in your document, then press ENTER. 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:
:wqTo exit and not save anything (lose all changes you have made since the last save) do:
:q!But, try to save your file for later use. Practice saving, exiting, opening a file in vi again, etc.
Feel free to open this file again and practice using the vi commands listed above.
This is a rather complex topic. But, in a nutshell, under FreeBSD, when your machine boots processes (that is daemons or services) are configured and/or started like this:
/usr/local/etc/rc.d/script-name.sh start
at system boot time. They may, or may not look in /etc/rc.conf for configuration settings.
$ man rc
Then, you should probably read this again...
Now, if you want to start a process each time your machine boot you generally add an item to /etc/rc.conf to indicate this. For instance, if you wanted to enable the ssh daemon (server) each time your machine started then you would add the line:
to /etc/rc.conf. If you look at /etc/defaults/rc.conf you'll see that sshd is not enabled in this file by default. By enabling sshd in /etc/rc.conf this overrides the setting in /etc/defaults/rc.conf. In addition, if you look in /etc/rc.d/ you'll find an sshd script file that starts this service.sshd_enable="YES"
To see how sshd is enabled initially do this:
$ grep sshd /etc/defaults/rc.conf
You should see something like:
These are the lines in /etc/defaults/rc.conf that deal with the ssh daemon. When you specified to enable the ssh daemon during installation then in the file /etc/rc.conf the lines that read:sshd_enable="NO" # Enable sshd sshd_program="/usr/sbin/sshd" # path to sshd, if you want a different one. sshd_flags="" # Additional flags for sshd.
became active. So, if your ssh program was not "/usr/sbin/sshd" for some reason, then in /etc/rc.conf you could add:sshd_program="/usr/sbin/sshd" # path to sshd, if you want a different one. sshd_flags="" # Additional flags for sshd.
to override what's in /etc/defaults/rc.conf.sshd_program="/new/directory/sshd" # new path to sshd
You could just put everything in /etc/defaults/rc.conf, but you don't want to do this. If you upgrade your system it's almost certain that /etc/defaults/rc.conf could be overwritten. In addition, this file is large and it would be hard to see the changes you had made if you were to do them in /etc/defaults/rc.conf.
For the following exercises you must log in to a terminal as root.
To start a service manually you can use it's startup script by hand. For instance, try typing:
# /etc/rc.d/sshd
What is returned on the screen? It should be something like:
So, you could typeUsage: /etc/rc.d/sshd [fast|force|one](start stop restart rcvar keygen reload status poll)
# /etc/rc.d/sshd status
to see if ssh is running. If it is, then try:
# /etc/rc.d/sshd stop
to start the service. Now type:
# /etc/rc.d/sshd start
to restart the service. Note the startup script option "reload" - This would let you make changes to the ssh configuration file(s) and then reload the service without actually stopping it so that it reads the new configuration. Note that already connected clients would not see this new configuration change until the logoff and log back in again.
Finally, and this is not obvious, if a startup script in /etc/rc.d has not been enabled in /etc/defaults/rc.conf or /etc/rc.conf, then even if you manually invoke the script it will not run. You will not get any indication of this other than the service not starting (i.e. use "ps auxw| grep servicename" and you won't see it started).
At this point take a closer look at /etc/rc.d/
# ls /etc/rc.d
and use "man" to read about some of the services. If you want to try and start and stop some of these services feel free to do so now, but remember you'll need to add 'servicename_enable="YES"' in /etc/rc.conf for the service to start.
11.) Shutdown and reboot your system [Top]
For this exercise you need to be root. It is better to close open files and programs (for example 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
Now, in a terminal do the following (save data, etc. as this will immediately reboot your machine!):
# shutdown -r now
Now your machine is rebooting. The "-r" stand for "reboot" and the "now" meant to take this action "now". This takes a moment. To stop your machine entirely you can use the command:
# halt
But, if power management is not properly supported you may still need to press the power button to fully shut off your machine.
Or, you can also change your run level to run level 0, which is the same as "halt". So, you would write:
# init 0
And, to reboot this is the same as init 6, or:
# init 6
If you are running something like gdm for a graphical
login prompt on your machine you can usually use the provided menu choices
to reboot or shutdown. The thinking is that once you have this level of
access, then you can simply turn off the machine's power if you wish.
At the very least it is much more friendly to use a software interface
to shutdown or reboot than pulling the power as processes have a chance
to clean up, save data, etc.
Note, sometimes it is useful to bring your machine down to runlevel 1, or "single user mode". For instance, if you are running X Windows and want to shut it down quickly (you'd really only do this on a desktop machine, by the way!), then you can open a terminal window as root (or use "su"), and then type"
# init 1
This will shut down X Windows, networking, and quite a bit more. Now you are in "single user mode". To get back to "multi-user mode" you simply type:
# exit
This exits your single-user mode shell and tells the system to go back to multi-user mode.
To view the status of your network interfaces you use the command ifconfig. If you have an ethernet card, then, in general, you will see two network devices when you type the command:
$ ifconfig
Here is a sample output from this command on a laptop that uses a Lucent wireless card: