Basic Linux Commands
Note: This primer is an expansion of the Linux Primer
that is included in the article “Simple Steps to Implementing GroupWise
6.5 For Linux”. This article can be found in the 2004 March/April
issue of Novell
Connection Magazine.
Just as soon as you begin learning Linux, particularly if you are a systems
administrator, you will need to learn how to navigate through Linux at
a “terminal/shell” session. Inside a terminal prompt you issue
commands to the Linux operating system. A terminal session is very much
like a DOS prompt. However Linux has significantly more utilities than
you would use at the terminal prompt.
All installations of Linux have a terminal solution of some sort. Most
GUI installations of Linux place an icon for a terminal prompt in a very
noticable place. For example on a SUSE LINUX Professional 9.0 distribution
with a KDE Desktop, the icon for a terminal/shell session is right on
the toolbar at the bottom of the screen. It looks like a shell in front
of a computer screen, as shown in Figure 1 below.
Figure 1
On a Redhat Linux 7.2 distribution with a GNOME desktop, the icon for
a terminal/shell session is right on the toolbar at the bottom of the
screen. It looks like a footprint in front of a computer screen as shown
in Figure 2 below.
Figure 2
Important Note: Linux is case sensitive. So you when
you run commands or deal with files, make sure to keep case sensitivity
in mind.
Following is a table of the basic commands that you will need immediately
when administering Linux. These commands are executed within a terminal/shell
prompt.
| Common Linux terminal/shell Commands |
| Task |
Command |
Example |
DOS Equivalent |
| list the contents of a directory |
ls |
List all files in a directory: ls
List all files in a directory which start with “gw”: ls
gw*
List all files and their sizes in a directory: ls –s
List files in a directory with verbose information about the files:
ls -la
|
dir
or
dir gw* |
| print the name of the current working
directory |
pwd |
print the name of the current working directory: pwd |
chdir |
| change directory |
cd |
Change to the root directory: cd /
Change to the /etc directory: cd /etc
|
cd or cd etc |
| make a directory |
mkdir |
Make a directory called “dir1”: mkdir dir1 |
md dir1 |
| delete/remove a directory |
rmdir |
Delete or remove a directory called “dir1”:
rmdir dir1 |
rd dir1 |
| read a file and display it on the screen |
cat |
View the contents of file.txt: cat file.txt
The file has a lot of text that scrolls by and you want to view it
screen by screen: cat file.txt | more
|
type or
type file.txt | more
|
| find a file or directory |
find |
Find the “file2.txt” file that is located somewhere
on your Linux server: find / -name file2.txt
Find the “Novell” directory that is located somewhere
on your Linux server: find / -name Novell
|
No direct equivalent DOS command |
| move a file to a new path |
mv |
Move the “file.txt” file from the
/temp directory to the /etc directory:
mv /temp/file.txt /etc
|
move file.txt c:\temp |
| rename a file |
mv |
Rename the “file.txt” file to “TESt1.txt”:
mv file.txt TESt1.txt
|
ren file.txt test.txt |
| delete/remove a file |
rm |
Delete/remove “file.txt”: rm file.txt
|
del file.txt |
| break out of a process |
Ctrl-c |
You used a command and now you want to break out of it: Hold down
the Ctrl key and the c key. |
Ctrl-c |
| clear the screen |
clear |
Clear the current terminal screen: clear |
cls |
| find a command that will help you to do something, but you don’t
know the name of the command |
apropos |
Find commands related to creating a zip file:
apropos
zip
|
The help command is somewhat like apropos |
| print help information regarding a command |
-help |
Many shell-based utilities (not all) will print a help screen by
adding the -help switch to the end of the command.
For example:
ls -help
|
/? |
| Sometimes there’s just too much information or text coming
at you. The “grep” command helps you
filter the information. (See example) |
grep |
Find commands related to zip files, but with specific mention to
“gz”: apropos zip | grep gz
|
No direct equivalent DOS command |
| copy a file to another location.
|
cp |
Copy file.txt from the current location to the /usr/local directory:
cp file.txt /usr/local |
copy |
| Quickly view a text file |
more |
View the file called file.txt. Use the Enter key to advance through
the file, and the Ctrl-c key sequence to break out of viewing the
file. Here’s the syntax for viewing a file: more file.txt
|
type file.txt | more |
Running Programs in Linux
Like most operating systems Linux has search paths. If you want to know
the search paths in your Linux installation, you can type the following
command at a terminal/shell prompt:
set
Look for the “path=” statement, and you will generally see
a lot of different paths stated after the “path=” statement.
Programs that are in the search path can be executed from a terminal
session independent of what directory you are in. However if you want
to execute a piece of software that is not in the search path you must
indicate the path to the executable. For example, let's say I'm in the
/usr/home directory, but I want to exectue a shell script in the /temp
directory called “run.sh”. Here is the command I would use:
/temp/run.sh
Even if my current location were the /temp folder, I still need to indicate
that the path to the folder that I am in order to execute the run.sh file.
The “.” (period) character stands for the current directory.
So if I am currently in the /temp directory, and I want to execute the
“run.sh” file I would use the following syntax:
./run.sh
Sometimes you might download a file, but you cannot execute the file.
Generally this means you must “change the mode” of the file
so that the Linux will allow the file to be executed. You can use the
“chmod” utility to do this. With the following command you
can change the mode of a file called “script1.sh” so that
it can be executed:
chmod 755 script1.sh
Issuing the chmod command above tells Linux to allow the file to be executed.
Many programs in Linux do not have a user interface. So if you happen
to load a process, and you want to determine whether the process is running,
then you can use the “ps” command. For example:
ps -eaf
Most likely there will be many processes will fly by, you may want to
pipe the information to more utility. For example:
ps -eaf | more
Working with *.TAR.GZ Files
The gzip utility can zip and unzip *.tar.gz files. After running the
gzip utility to decompress a file with a *.tar.gz extension, the file
will be called <filename>.tar. The file must then extracted from
it’s *.tar format using the utility called “tar” which
is explained next. Here’s an example of how to use gzip to decompress
a *.tar.gz file:
gzip –d java2.1.tar.gz
Note: The –d argument instructs gzip to decompress the *.tar.gz
file.
Working with *.TAR files
The *.tar (tape archive) format is a popular format in the Linux/Unix
world. A file with a *.tar extension is one file that usually has more
than one file within it. But *.tar files are are not smaller than the
total size of the files within the *.tar file. So often a file that has
been “tarred” is then compressed via gzip. At that point the
*.tar file becomes a “*.tar.gz” file. Here’s the command
to untar a *.tar file:
tar –xvf java2.1.tar
The argument “x” means extract. The argument “v”
means be verbose while processing the *.tar file. The argument “f”
basically means to extract the contents of the *.tar file specified just
after the “f” argument.
Working with *.RPM Installation Files
The *.rpm file extension is an installation file that complies with the
very popular Linux installation standard called Redhat Package Manager.
All of the installation routines and software to be installed are contained
within the *.rpm file. Following is an example command line to process
a *.rpm file:
rpm –ivh groupwise-gwclient-6.5.1-i386.rpm
The argument “i” means install. The argument “v”
means be verbose while processing the *.rpm file. The argument “h”
means while the rpm is installing the software it should indicate the
installation progress by displaying hash marks (pound symbols).
Sometimes you might have installed the software before, and you want
to re-install it. By default the rpm utility won't allow that. If you
try to run rpm and it reports that you cannot install the software because
of a prior installation, you can use the --force argument (that's a double
dash). Here is an example of incorporating the --force argument with rpm:
rpm –ivh --force
groupwise-gwclient-6.5.1-i386.rpm
Working with *.BIN Installation Files
Although the *.rpm installation file format is popular (as explained
in the previous section) sometimes you will have installation files with
a *.bin extenson. These type of installation files do not need an install
utility, they just need to be run like any other exectuable. For example
if I have the file”j2sdk-1_4_2-nb-3_5_1-bin-linux.bin” in
my temp directory, and I am currently in the temp directory I would use
the following command to execute the file:
./j2sdk-1_4_2-nb-3_5_1-bin-linux.bin
The installation behavior of a *.bin file is up to the manufacturer
of the bin file. So the instllation behaviour you get from a *.bin file
will necessarily be consistent.
There you have it. There are so many more commands in Linux, but this
list is enough to help you get really comfortable with Linux. I have perused
several Linux books, and purchased three. By far the one that I like the
most is the O'Reilly book Linux In A Nutshell by Siever, Figgins&
Weber.
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