Linux Commands

There are of course thousands of Linux related commands and procedures. I will give a few of the more common ones here but I assure you there is A LOT more to Linux than just these relatively simple commands. A few tips with Linux type man command to get an extensive help file. For example type 'man ls' to get the manual page for the ls command containing information on the various switches and uses of the ls command.
You can also execute multiple commands by separating each one with a ; for example cd newdir; mkdir thatdir ; ls -la will first change directories to the newdir directory, then create a directory called thatdir, then list all the files in long format. You can string together as many commands as you like but caution should be used not to inadvertently do anything harmful.
Contents
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cd  chmod  cp  df  dir du  find  head  kill  less  ls  mkdir  more  mv  ps  pwd  rm
rmdir  tail  top  tree  vdir  vi  xload

cd
This command is used to change the directory and using this command will change your location to what ever directory you specify
cd hello
will change to the directory named hello located inside the current directory
cd /home/games
will change to the directory called games within the home directory.
As you can see you can specify any directory on the Linux system and change to that directory from any other directory. There are of course a variety of switches associated with the cd command but generally it is used pretty much as it is.
Type man cd for more information on the cd command.
See also ls  dir  vdir
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chmod
This command is used to change the mode for files to know more about this command go to the Permissions (Setting up the mode)section. You can get there by using this link chmod you will need to use the back button (or go through the linux home page menu) on your browser to get back here).

cp
The cp command copies files. You can copy a file in within the current directory or you can copy files to another directory.
cp myfile.html /home/help/mynewname.html
This will copy the file called myfile.html in the current directory to the directory /home/help/ and call it mynewname.html.
Simply put the cp command has the format of
cp file1 file2 With file1 being the name (including the path if needed) of the file being copied and file2 is the name (including the path if needed) of the new file being created.
Remember with the cp command the original file remains in place.
Type man cp to see more about the cp command.
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df
The disk free command shows how much memory is being used and how much is free for every partition and mounted file system (including any Windows drive/s).
Type man df for more information about the df command.
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dir
The dir command is similar to the ls command only with less available switches (only about 50 compared to about 80 for ls). By using the dir command you will get a listing of the contents in the current directory listed in columns.
Type man dir to see more about the dir command.
See also cd  ls  vdir
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du
The disk usage command shows how much memory is being used by each directory below that from which the command was given. If du is run from the root directory it will show the memory used by every directory on the system, including any mounted file systems (including other drives) such as any Windows related drives.
Type man du for more information about the du command.
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find
The find command is used to find files and or folders within a Linux system.
To find a file using the find command you type
find /usr/bin -name filename
this will search inside the /usr/bin directory (and any sub directories within the /usr/bin directory) for the file named filename. To search the entire filing system including any mounted drives use
find / -name filename
and the find command will search every file system beginning in the root directory.
The find command can also be used to find command to find files by date and the find command happily understand wild characters such as * and ?
Type man find for more information on the find command.
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head
The head command list the first lines of a file. By default it will display the first ten lines of a file.
For example head filename
will list the first ten lines of the file named filename.
You can also select how many lines to show
for example
head -5 filename
will list the first 5 lines of the file named filename.
The format for the head command is 
head -n filename With the number of lines to be displayed being n and the file name of the file, including the path if needed, you wish to view being in place of filename.
Type man head for more information on the head command.
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kill
The kill command is used to kill a process by using the associated PID (Process ID) number
e.g.
kill 381
This will kill the process with the PID of 381. Be careful using the kill command because it is easy to accidently kill an important process.
To see the current list of processes that are running use the ps command. Typing ps au will display every process that is in operation including background processes and those being conducted by other users.
See also ps  top
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less
This command allows you to scroll through a file a page at a time. The less command is very similar to the more command only it is more advanced and has more features associated with it.
less filename
Type man less for more information on the less command.
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ls
The ls command lists the contents of a directory. In its simple form typing just ls at the command prompt will give a listing for the directory you are currently in. The ls command can also give listings of other directories without having to go to those directories for example typing ls /dev/bin will display the listing for the directory /dev/bin . The ls command can also be used to list specific files by typing ls filename this will display the file filename (of course you can use any file name here). The ls command can also handle wild characters such as the * and ? . For example ls a* will list all files starting with lower case a ls [aA]* will list files starting with either lower or upper case a (a or A remember linux is case sensitive) or ls a? will list all two character file names beginning with lower case a . There are many switches (over 70) associated with the ls command that perform specific functions. Some of the more common switches are listed here.

Switches can be combined to produce any output you desire.
e.g.
ls -la
This will list all the files in long format showing full file details.

Type man ls for more details about the ls command.
See also cd  dir  vdir
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mkdir
The mkdir command is used to create a new directory.
mkdir mydir
This will make a directory (actually a sub directory) within the current directory called mydir.
Type man mkdir to see more about the mkdir command.
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more
This command allows you too scroll through a file one screen at a time allowing you to more easily read the files contents. Some files are very big and using this command allows you to view the contents of large files more efficiently. To go forward one screen use the space bar and to go back one screen use the B key
more filename
Type man more for more information about the more command.
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mv
The mv command moves files from one location to another. With the mv command the file will be moved an no longer exist in its former location prior to the mv. The mv command can also be used to rename files. You can move files within the current directory or another directory.
cp myfile.html /home/help/mynewname.html
This will move the file called myfile.html in the current directory to the directory /home/help/ and call it mynewname.html.
Simply put the mv command has the format of
mv file1 file2 With file1 being the name (including the path if needed) of the file being moved and file2 is the name (including the path if needed) of the new file being created.
Type man mv to see more about the mv command.
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ps
The ps (process status) will by default only show the processes that you as a user have started. However Linux is always running background tasks so you may want to use some of the common switches associated with the ps such as ps au to display the processes running for all users and in the user format hence we get to see every process that is running on the system.
When a process is started it is given among other things a PID number that is unique to it. This PID number can be seen by using the ps command or top command. By knowing a Process ID number you may opt to kill the process if you choose.
See also kill  top
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pwd
The pwd command (print working directory) will display the current directory.
e.g.
typing
pwd
will display something similar to this /home/games/help
being the details of the current directory.
To get help with the pwd type /bin/pwd --help and a short help file will be displayed. Type man pwd to get more information about the pwd command.
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rm
The rm command is used to delete files. Some very powerful switches can be used with the rm command so be sure to check the man rm file before placing extra switches on the rm command.
rm myfile
This will delete the file called mydir. You can include a path to delete a file in another directory for example rm /home/hello/goodbye.htm will delete the file named goodbye.htm in the directory /home/hello/.
Some of the common switches for the rm command are

Type man rm to see more about the rm command.
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rmdir
The rmdir command is used to delete a directory.
rmdir mydir
This will delete the directory (actually a sub directory) called mydir.
Type man rmdir to see more about the rmdir command.
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tail
The tail command list the last lines of a file. By default it will display the last ten lines of a file.
For example tail filename
will list the last ten lines of the file named filename.
You can also select how many lines to show
for example
tail -5 filename
will list the last 5 lines of the file named filename.
The format for the tail command is
tail -n filename With the number of lines to be displayed being n and the file name of the file you wish to view, including the path if needed, being in place of filename.
Type man tail for more information on the tail command.
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top
Either typing top at the command prompt or selecting top from the xwindows menu will activate the top application. Top simply lists all the operations in progress showing memory usage by each process. You have the option to kill any process if you want to but be careful if you kill a vital system you will run into trouble and may at the very least have to reboot to fix it.
Typically top is run in a spare xterm or x11 window while doing other tasks. To access the help in top use the ? or H key. To kill a task use the K key or change the priority of the task by using the R key.
Type man top to see more detailed information about the top command.
see also xload
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tree
This will give a graphical display of the structure of a particular directory and all sub directories, files and links within that directory.
e.g.
tree /var/lib
will show something similar to this

/var/lib
|--games
|--rpm
|   |--conflictsindex.rpm
|   |--fileindex.rpm
|   |--groupsindex.rpm
|   |--packages.rpm
|   `--require.rpm
`--text

6 directories, 6 files

Type man tree for more information on the tree command.
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vdir
The vdir command is similar to the ls -l command. When used the command acts very much like ls -l does by displaying the directory contents showing the file attributes and permissions. The amount of switches for vdir are a lot less than for the ls command (vdir has just over half the amount of available switches as the ls command) but vdir is still used and accepted.

Type man vdir to see more about the vdir command.
See also cd  dir  ls
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vi
The vi command is actually a text editor that comes as standard with most Linux packages.
Type man vi for more information on vi.
More information on vi is in the Using the vi Editor section. Use this link vi to get there .
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xload
Either typing xload or selecting xload from the xwindows menu (if it is available) will activate the xload feature in a x11 window. The xload application provides a running graph of the system load. Often it is easier to tell if a system is overloaded by having a visual aid to see the load on the system. The xload command has eight different command line options and can be customized in regards to colour, scale and background.
Typically xload is run as a background task to enable visual monitoring of the system load.
Type man xload to see more detailed information about the xload command.
see also top
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