first off lets open a terminal in gnome click on application -> accessories -> terminal (kmenu -> system -> konsole for kde)
To switch between the terminal and your IRC client using only the keyboard you can use "alt and tab" to cycle through the active windows.
I want to introduce the concept of a shell <
>
you have in front of you in the default black writing on a white background on the left there is something that looks like this
{{{
ompaul@desktop:~$
}}}
this is your username at your machine and it currently indicates you are in your home directory <
>
if you type at that {{{ command set | grep SHELL }}} you will see that the first line returned is {{{ SHELL=/bin/bash }}}
that indicates what "shell" your "environment" is set to use <
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this is the program that you use to converse with the kernel <
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this program provides a programming environment (usually in the form of scripts) to allow a user to interact with the machine and manipulate it <
>
there are two ways it does this: <
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it invokes command within itself <
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or it can invoke commands external to itself <
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the ones within are referred to as "buildins" <
>
so the first command I want you to in there now is `pwd` <
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this command tells you where you are <
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pwd is hard to remember but it actually stands for print working directory <
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now you may see from time to time things such as {{{ ls -al }}} the part after the ls is called an argument <
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pwd accepts two arguments <
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the first is --help - which displays help for the program and <
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the other is --version - which displays the version number <
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after both of these functions have completed (and providing they complete correctly) the program exists <
>
please run the following
{{{
pwd --help
}}}
[PWD has a bug --help doesn't work, we move on to another command]
to demonstrate an argument let us use the command which invokes manuals <
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this is the "man command" <
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please type {{{ man --help}}} in your terminals now
you will notice that a lot of data is on the screen and the scroll bar on the right should indicate that some data has passed by however we do not always have the luxury of a scroll bar so now we will have a quick look at how to see more data
so to see the data one screen at a time you can do this:
{{{
man --help | more
}}}
the function of that pipe (|) is to take the output from `man --help` and then present it to the command `more` <
>
what more does is it allows output to be viewed one screen at at time <
>
if you press the down arrow the screen will scroll down one line at a time and if you use the space bar it is one page at a time <
>
however more faces a restriction a big restriction - you can only move in one direction - it only allows you to go down
we can do "more than more" by using a new command less <
>
the benefit of less is that we can go up and down <
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we can use up and down arrows and page up and page down <
>
this is useful of you have lots of data
so if you do {{{ man --help | less }}} you can test this you can navigate up and down and then to quit you can press `q`
now lets have some fun
please type {{{ man man }}} <
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on the foot of the screen you will see something like this
{{{ Manual page man(1) line 527/551 (END) }}} <
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this indicates what manual page you are looking at before the bracket(1) in this case man, and it also lets you know how big the manual page is the last number, in this case 551 <
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although the manual pages are written in a very "tight" style, if you get used to them you will find them good friends to discover options when you try to do something more complex <
>
now please press `q` and exit that man page <
>
firstly let me tell you something of the layout of linux as it will help you understand some of what is there in front of you <
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when I say layout just now referring to the filesystem <
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you are currently in what is called your home directory <
>
the prompt is as I showed eariler
{{{
ompaul@desktop:~$
}}}
the ~ after the : is short hand for saying `/home/your_username/` <
>
the word directory in english actually means "list" however to be clear about what a directory is I like to think of the hard drive as a filing cabinet <
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there are many drawers in the filing cabinet each of the drawers can contain more drawers <
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to see the list of "primary drawers" we can use the command `ls` which is short for list <
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the whole cabinet is called `/` which we call "slash" not forward slash but slash <
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this `\` is "back slash" <
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there is no forward slash :)
that must be something else you are thinking about :)
so let us get a list of the things in /
{{{
ls /
}}}
Q: is there a meaning for the colors of the dirs and files after ls ? <
>
A: there is, but lets not get ahead of ourselves
so you see bin <
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it is the first directory there <
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so now please do
{{{
ls /bin
}}}
the colour you see for bin indicates it is a directory <
>
you are now looking at the contents of /bin <
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you can see some very common every day commands there <
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ls is there <
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date <
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ps (which shows what processes are running on the computer when given certain arguments) <
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tar touch sed and a lot of others <
>
the colour you see for arch and bash and most of the others in there is for an executable file <
>
depending on how your console is set up but in general, green <
>
{{{
ls -al /bin/bash
}}}
{{{
-rwxr-xr-x 1 root root 664084 2006-04-21 23:51 /bin/bash
}}}
that is what it replies or something like that
you will notice that the there are several letters on the left hand side of the screen and some dashes <
>
they are the file permissions <
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r = read from the file | w = write to the file | x = execute (run) the file <
>
you may notice that I say file <
>
and also you may remember I referred to "drawers containing drawers" <
>
well directories have file permissions too <
>
in fact directories are nothing more than fancy files that contain more files <
>
and they too have permissions <
>
if you run
{{{
ls -l / | grep bin
}}}
you will get back something like:
{{{
drwxr-xr-x 2 root root 4096 2006-07-12 17:50 bin
drwxr-xr-x 2 root root 8192 2006-08-18 23:37 sbin
}}}
now on the extreme left of the permissions you will see the letter d <
>
this indicates that these files are directories
so now you have two concepts: files and directories <
>
you have also a concept of permissions, however not in detail
you will notice if I take the /bin/bash permissions that it starts with a - <
>
then it has the first group of three rwx <
>
then a group with r-x <
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and another group with r-x <
>
well reading left to right we call these groups <
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Owner Group World (or I have heard it called Everybody) <
>
so what does this mean? <
>
well this gets more meaning from the two columns after the number 2 <
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root root <
>
this is the owner of the file and the group that the file is owned by <
>
root owns the file and also there is a group called root <
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they are not the same :) <
>
in some cases <
>
like where your username is the group <
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I will break it out into little blocks
so in your own home directory there are files
Q: the file is owned by a user called "root" and the file is also owned by a group called "root" ? <
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A: yes <
>
Q: by group root.. u mean the username? <
>
A: no, explanation is to come
please type `ls -al /etc/group`
first off note that it is not executable <
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second note that while any one in the group root anyone (everybody/world) can read it <
>
so it is readable by all users on the computer <
>
now let us look inside that file
{{{
less /etc/group
}}}
first line <
>
root:x:0: <
>
so this is a group <
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the group has a numerical id it is 0 (as seen in the output) then as you look down the file you will see your username it will be a member of some of the groups in the machine. <
>
On ubuntu group 106 admin, for instance, is occupied by users who have "administration powers" <
>
if you press the space bar you will get to the end of the file
you will see the first user created on the machine as a group name = the username and with a GID (group id number) of 1000
in a business you might have a group sales <
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and they would all be able to access the files belonging to the group "sales" <
>
now the reason we went down this road (and whole chapters in books have been written about permissions) <
>
was to explain that a file has an owner (as in a user) and a group owner and these things can be used to grant access to the users on the box or deny them access to a file <
>
this is important because if you can't run a file you may be trying to access something that the system will not allow <
>
so now in your home directories <
>
all that information in a way that people don't usually "see" is <
>
please type
{{{
stat Desktop
}}}
{{{
ompaul@desktop:~$ stat Desktop/
File: `Desktop/'
Size: 4096 Blocks: 8 IO Block: 4096 directory
Device: 303h/771d Inode: 4653091 Links: 7
Access: (0755/drwxr-xr-x) Uid: ( 1000/ ompaul) Gid: ( 1000/ ompaul)
Access: 2006-08-20 12:20:29.000000000 +0100
Modify: 2006-08-20 08:05:46.000000000 +0100
Change: 2006-08-20 08:05:46.000000000 +0100
}}}
okay you will see the file name at the top <
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I said eariler that directories were files <
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you will see Desktop/ being called a file <
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now for the most mind blowing thing you will ever learn about linux and unix based systems (at least in my opinion) <
>
'''EVERYTHING IS A FILE''' <
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and I mean that. your screen, your keyboard, your mouse, they can be read, written to. your printer, your usb key, the whole system is a collection of files. You take data and you move it from one place to another this all goes back to an early design choice and it was very fortunate for us they choose that what it means is that you can take the output of a file and redirect it to another you an then add to it subtract and a whole lot of other things <
>
I will demonstrate that next
first off let us create a file in our home directories. <
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the way to create an empty file is to use the `touch` command <
>
it is normal to refer to random files as "foo"
please type `touch foo123` in your terminal <
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now stat it <
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the inode data there is its actual address on the file system <
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which contains the info about where the file lives on the system <
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as you note the file is owned by you <
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it is readable and writable by you <
>
it is readable by the group and anyone on the machine <
>
you remember eariler we used `man --help` <
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well let us capture that data in the file foo123 <
>
so do this
{{{
man --help > foo123
}}}
we can now look at the file with stat <
>
or we can do it the way most people do it
{{{
ls -l foo123
}}}
right now it looks like `-rw-r--r-- 1 ompaul ompaul 2390 2006-08-20 12:45 foo123` <
>
the 2390 is the size of the file <
>
lets overwrite <
>
but first have a quick look
{{{
less foo123
}}}
press the space bar until you get to the end <
>
then press q to get out of less
so do this
{{{
wc foo123
}}}
now what do you think your looking at? <
>
lets find out what your looking at
{{{
man wc
}}}
what does that tell you <
>
wc - print the number of newlines, words, and bytes in files
so it tells you the lines that are in the file <
>
please press q to leave the man page <
>
so we have seen the original stat data of the file <
>
lets look at that
{{{
stat foo123 >> foo123
}}}
that should be fun <
>
after that type `wc foo123`
okay so when we type `wc foo123` we note that the line has a size <
>
then if we do the next part: `stat foo123 >> foo123` <
>
we add the stat info onto the end of the file <
>
so the point here is that the > single redirection pipe <
>
takes some "random input" and puts it into the file "in this case foo123" <
>
when we use the >> this APPENDS the additional data to the file <
>
in this case we got it to add on the contents for foo123 to the tail end of the file <
>
you can see this if you now type `less foo123`
now that is three pipes covered <
>
"A | B" take the data from the left (A) and hand to the the program on the right (B) to be processed <
>
we have also taken random data and put it into a file <
>
usually that is output we want to capture to analyse for later <
>
that is done with the > <
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and then we can open an already full file and append data to it <
>
this is the >> <
>
NOTE the > overwrites all previous data <
>
ls <
>
ls -al <
>
| <
>
> <
>
>> <
>
touch <
>
man <
>
and the concept of an argument <
>
now to find your way around the file system <
>
you are in your home directory <
>
you can move from there to your desktop <
>
so in the terminal please type
{{{
cd Desktop
}}}
you have now moved to the desktop <
>
if you `touch foo1234` here you will create an empty file on your desktop <
>
please do so and check it exists by minimising your irc window
to explain some more about where you are please consider the file system to be like this
{{{
/ <---- also referred to as root
/home/ <---- this is where all the users home directories live
/ompaul/ <-- as it is in my case - this will be your username :)
/Desktop/ <-- note the capital D
}}}
the full path is <
>
/home/ompaul/Desktop/ <
>
now we also know about /bin/ <
>
there are hundreds of directories on the machine <
>
and thousands of files (if not millions) <
>
now
{{{
cd /
}}}
takes you to the root of the file system <
>
you do not want to be creating things there <
>
in fact you do not have rights to create data in that directory <
>
the place you should create data is in you own directory or some subdirectory below that <
>
now if you are in the Desktop directory you can create a new directory in that <
>
mkdir myfirstdirectory <
>
you can then enter that <
>
{{{
cd myfirstdirectory
}}}
so now you are within that location <
>
lets do something <
>
lets use the `df` command which tells us information about the file system layout <
>
but lets make it human friendly output <
>
do the following
{{{
df -h
}}}
now if you want to compare how much disk space is used over time <
>
we can record the disk space used today <
>
so do this
{{{
df -h > dfinfoAug20-2006
}}}
so this gives us as humans a file we can relate to <
>
now if you go to your desktop and click on myfirstdirectory <
>
you can find the file we just created in it
okay lets make a copy of that file into our home directory in the terminal <
>
type this much only
{{{
cp df
}}}
now hit tab key <
>
see it complete the file name <
>
now you want to get it into your home directory <
>
{{{
cp dfinfoAug20-2006 /home/ompaul/.
}}}
note the dot at the end
I could change its name with this
{{{
cp dfinfoAug20-2006 /home/ompaul/MyNewName
}}}
or even do this
{{{
cp dfinfoAug20-2006 ~/.
}}}
which is the same as the first one
the dot means "keep the same file name" <
>
but .is is a hidden file called .is :)
{{{
ls -al
}}}
the a means hidden and the l is long format (give lots of detail)
(at this point all the Students left, and the class gets cut short)
For more information see: https://help.ubuntu.com/community/BasicCommands