Basic guide on using commands in Linux console (Terminal)

Intro:
After my successful move to Debian I was trying to write complete HOWTO on how better move from Windows to Linux, but since I can't finish it for a long time, I decide to wrote short guide on using commands in console which could help for a person new to this OS use console or perform actions via SSH(could be useful if you use Linux based hosting).
It just my small contribution to big Linux community

I'm using Debian Etch(Testing branch) so this guide is written in mind with it, but since almost all of these commands are distribution independent they should work for all Linux distributions, and other *nix systems. So here few "secrets" I'd like to share hope they would make your life easier Wink

Few things useful to know:
Ok let's start. Linux is multitasking system, and unlike with Windows, in Linux multitasking starts in console(text mode you see if X Server isn't started). Most distributions set by default to run 6 virtual terminals, you can switch between them ALT+F1, ALT+F2, and so up to F6. You can perform in each of these terminals separate task.
ALT+Fn combination would only work if you're in console.
IMPORTANT: if you're running X Server CTRL+ALT+Fn combination should be used in order to get to console, and in order to return back to GUI hit ALT+F7 or CTRL+ALT+F7
Alternatively you can execute most of these commands when you're in X, just use Gnome Terminal(if you're using GNOME as GUI) or konsole if KDE.

“#” and “$” signs were used only to show whenever tool could be used by user or admin only, don't re-post them in terminal.
“$” sign before command will be used for commands which could be executed by unprivileged user.
“#” sign will be used before commands which should be executed by root user

File System Commands:
$ ls
used to show files and directories

$ ls /home
show content of home directory

$ ls -la /etc
adding “l” argument would show content inside /etc directory along with information about permission and modification time, adding “a” would show system files as well.

Tip: if you see too many files which doesn't fit into one screen you can either use “CTRL+ALT+PgUp” and “CTRL+ALT+PgDown” to scroll up and down your console. You can also try to execute list command like this:
$ ls | more
this will let you manually scroll text
or
$ ls | less
scroll text using your cursor and PgUp, PgDown keys. this utility is more handy than more IMHO, but it's not installed by default sometimes, in order to do it in Debian just execute as root this:
# apt-get install less

$ ls -la / > ~/ls_output
it's another way to save output of any command to file, as can you see it's very simple.

$ cat ~/ls_output
list_output will contain all output of ls command and you'll be able to view it with any text editor or just like this.

cd - abbreviation for change directory, as appear from this it let you move across file system.
$ cd /
change current directory to root directory “/” - the highest point of file system.

$ cd ..
move you up to one directory.

$ cd ~
change current directory to your home catalog using tilde "~" in this case would be equal to $ cd /home/your_username. Tilde is just a kind of shortname for current user home directory path.

cp (copy is used to copy files or directories)
$ cp /old_file_path/file1 /new_file_path/file1copy
this will copy file named "file1" from "/old_file_path directory" to "/new_file_path" but with new name "file1copy"

$ cp file1 /new_file_path/
copy "file1" from current directory to "/new_file_path" directory without changing it's name

$ cp /path_to_file/somefile .
if you put dot "." symbol as second argument it will copy file to current directory.

$ cp -R path /newpath
"-R" argument should be added in order to copy directory to another place, if you try to copy one directory to another “cp: omitting directory `path/'” error message will appear.

mv (used to move or rename files and directories)

$ mv oldfilename newfilename
rename oldfilename to newfilename

$ mv /old_file_path/file1 /new_file_path/file2
this will move file named "file1" from "/old_file_path" directory to "/new_file_path" and change it's name to "file2"

$ mv file1 /new_file_path/
move "file1" from current directory to "/new_file_path" directory without changing it's name

rm (removing files or directories)
$ rm file1
will remove file named "file1" from current directory

$ rm -R directory1
remove directory1 from current location, if you not provide -R key this message will appear: “rm: cannot remove `directory1': Is a directory”

TIP: If you remember DOS times and have used programs like Norton Commander, it could be worth to try mc(Midnight Commander) it have similar interface and features and could be helpful tool in learning new FS hierarchy.
to install it on Debian do this as root:
# apt-get install mc

Tip: If you only used Windows previously, Linux file system may confuse you a bit at first as it have different hierarchy. The main reason is that there are no drive letters like: “c:\”, “d:\”, etc. File system in *nix starting with point called root - “/”, all directories are placed under it.
All drives are mounted to point defined by user or program, e.g. your CD-ROM drive in most cases would be mounted to “/cdrom” so “$ ls /cdrom” would show files on your CD disk, floppy under “/floppy”, “/media/floppy”. If no programs for automating mounting are used default mount points could be defined in /etc/fstab file.
All devices e.g. mouse, disks, modem and the rest of devices in your PC are represented by special device files, here you can find more info on this: http://en.wikipedia.org/wiki//dev

Command Auto Completion:
There is very handy tool which help you save your time and fingers from typing extra characters.
E.g. you wish to change directory to /home just input:
$ cd /h
and now it's time to hit TAB button, this should complete your command to "$ cd /home/” isn't that handy?

Now let's say you don't know exact path, you don't have to waste time executing “ls” to find out what directories are available, just input:
$ cd ~/
and hit TAB again, you'll see all directories inside your user directory, now you just need to input first characters of directory you're looking and hit TAB again Wink

You also can complete commands itself, just try to input any letter and use TAB to see what commands starting with this letter.

Command history:
Another useful method of working in Linux console is utilizing history of commands you've entered. After entering some commands you can just hit cursor UP key. It will show previous command which you can edit and use again, it could really save a time if you use similar command for let's say different files or just made mistake and wish to correct it. Using DOWN key would return you next command.

Another way is to see list of all commands which was entered in console:
$ history
this will display list of last entered commands with ID numbers. To execute one command from the list, simply use ID number before it and put it after “!” sign. E.g. to execute command numbered 12, it's necessary to type:
$ !12

Estimating size of file or directory:
$ du -h somedirectory
above command would show size of directory

$ df -h
this one will display size of all partitions and free space on them

Finding necessary tool:
sometimes it could be tricky to find program you need to perform some task, try this:
$ apropos disk utility
this will display all commands which have keywords “disk utility” in it's description.
If you're using some Debian based distribution e.g. Ubuntu, Knoppix, Xandros, Simple MEPIS, Linspire, etc. you can try following command:
$ apt-cache search disk utility
This would display list of packages in known mirrors. (Tip: Frequently command have same name as package).

Edit text files:
Linux is heavily rely on configuration files in text format, so it's essential to know how to edit files in console. I prefer tool called Nano, to edit some file with it just type:
$ nano /somedirectory/filetoedit
this will open easy to use text editor which could really help sometimes.

If you have installed mc(Midnight Commander)installed you may use editor which comes with it:
$ mcedit /somedirectory/filetoedit
To install both programs mentioned above, execute as root this command:
# apt-get install mc nano

Dealing with archives:
There are a several ways to compress and uncompress files and directories in Linux, I'll show two most universal in my opinion. Let's start with archiving one file:
create some file e.g.:
$ ls > testarc
this would create file with name "testarc"

now let's archive it with gzip
$ gzip testarc
above command will compress file "testarc" and add .gz extension to it, so if you do $ ls you'll see file "testarc.gz" (original testarc file would be removed).

In order to decompress file to original one, simply execute:
$ gzip -d testarc.gz

It's possible to get better compression ratio using .bz2 archives but to achieve this use bzip2 tool. (In Debian just execute as root # apt-get install bzip2).
to compress:
$ bzip2 testarc

to decompress:
$ bzip2 -d testarc

Above way will work for single file only, if you put several files to compress like this:
$ gzip arc1 arc2
you'll get two archived files named "arc1.gz" and "arc2.gz"

If you need to compress directory, you'll need to use tar tool, unlike gzip or bzip2 it wouldn't affect your original file and would uncompress to separate directory or create new archive.
to compress some directories into .gz:
$ tar zcf compressed.tar.gz arcdir1 arcdir2
by this command will created file named "compressed.tar.gz" from "arcdir1" and "arcdir2" directories.
If you add “v” to arguments you'll see output of files added to archive.

to uncompress directory do:
$ tar zxvf compressed.tar.gz

To use .bzip2 tool for getting better compression try this:
to compress:
$ tar jcvf compressed.tar.bzip2 arcdir

to de-compress:
$ tar jxvf compressed.tar.bzip2

So as you can see from above commands “c” argument is used to compress and “x” to decompress, and “z” represent gzip archive and “j” bzip2.

Alternatively you can create archive without compression which could be useful e.g. for backing up data, this would also take less time comparing to using gzip or bzip2:
$ tar cvf compressed.tar arcdir

Finding file:
$ locate filename.txt
this command show location of file at glance because it's search for file using database where files from disk are indexed. There are drawback using this command as if you copy new files to hard drive locate command wouldn't be aware of this changes right away, to re-index new content you may execute:
$ updatedb

$ find /home -name filename.txt
will search "/home" directory for "filename.txt"
this command takes longer to show results but unlike locate it's always have updated info as perform searching in real time

$ which less
used to search for place where executable commands are placed, it will show only commands which are located in the PATH environment variable.

Few useful tools and shortcuts:
$ top
will show list of running processes

$ date
just to see what time is it now

$ uptime
how long your computer is running

$ cat /somefile |grep keyword
if you add "|grep someword" after some command you'll see output limited to strings where word "someword" is present.

Shortcuts:
CTRL+C
stop execution of program

CTRL+Z
terminate program, could help somtimes when CTRL+C wouldn't work.

CTRL+ALT+BackSpace
If you manage to hang up X Server, try following hotkey it would terminate X server and let you restart it once again.

Some useful Debian commands:
# aptitude
this is frontend for apt-get command, it will show you list of installed and available packages and let you remove or install new software easily)

# apt-get install packagename
install some package to your system

# apt-get remove packagename
will remove package

# dpkg-reconfigure packagename
will configure package, for some packages it will also ask questions about options you wish to use for certain package.

# dpkg -i package.deb
last command help you out if you download some file from the web and wish to install it, just point dpkg with “-i” argument to it and you'll get this package installed if all dependencies are met.

# pppconfig
small frontend which will help you configure your modem connection.

That's all for now, hope this short guide would be helpful and sufficient to start using your console.

If you have any questions, suggestions or feedback I'd be glad to hear them. Bug and mistake reports are very welcomed!
It could possibly help me out make this guide better.

BTW if you wish feel free to repost this guide, just remember to place a link to source Wink