Remote Access to a Linux Server
versions are available.
This document assumes you have completed the steps outlined in
the Linux Quickstart document.
and the Using Linux in JB 202
document. These documents are available
If that is the case then you have an active account on the Linux server
named csci.hsutx.edu and you have successfully made use of your
account by connecting from JB 202. For the remainder of this document I
will refer to the server as csci.
This document attempts to explain other ways in which you can connect to
the server to perform useful work. This will be helpful because the JB 202
lab maintains limited hours. There are other computer labs on campus that
have longer hours. One of those labs (JB 104) has software that will make
connecting to csci easier.
There are three protocols through which you can establish a connection to
csci (from off-campus):
- http (view web pages on csci using a browser)
- ssh (log in to csci and type commands using an ssh client)
- sftp (transfer files to/from csci using an sftp client)
Most people are familiar with making http (web) connections to
a server: to view a web page you simply start your favorite browser, enter
the URL of the site you want to contact, and voila, you have made a
connection to the server and it provides you with information.
In the same way, to make an ssh connection to the server you can
simply launch your favorite ssh client and enter the name of the
server to which you want to connect! Of course, there are two problems
with this advice:
- chances are, you do not have a favorite ssh client, and
- when you connect using ssh instead of being greeted with
friendly, graphical information, you are confronted with a
command-line interface that wants to know your username and
Allow me to address these issues invidually.
There are a variety of Windows-based ssh clients. One of the free
ones is Putty (available at http://www.chiark.greenend.org.uk/~sgtatham/putty/).
The remainder of the document is written assuming that you are using Putty.
I recommend that you do a full download and install so that you also get
the sftp client. NOTE: There are free ssh clients for the
Macintosh platform as well. One is http://www.macssh.com.
Once you download and install the program simply launch it and enter
the full server name (csci.hsutx.edu). Upon establishing a
connection, you will be prompted for your username and password. After
you log in successfully you will be greeted by the Linux command-line
interface. At this point it would be helpful if you knew a lot of Linux
commands! If that is not the case then you should turn your
attention to the next section.
There are two primary methods of dealing with a command-line interface:
- learn several useful commands, or
- run graphical programs that will perform the useful commands for
I have used the command-line interface for some time and, in fact, prefer
it to a graphical interface for many uses. If you are new to Linux then
this interface will be difficult to use at the beginning. One immediate
advantage over using a graphical interface is that no additional software
If you want a graphical user interface to run through your ssh
connection on a Linux server then you will have to install and run
an X-Server on your Windows computer. Here are some options (in order of
- Download and install the free X-Server called Xming. It is
available at http://www.straightrunning.com/XmingNotes/
- With a lot more hassle, another free alternative is
Cygwin/X which can be downloaded at http://x.cygwin.com/. The
installation process is somewhat painful and time-consuming because it
involves creating a mini-Unix system on your computer and the X-Server
is actually run within that environment. This means a big download
and lots of chances to screw up the installation.
- One ``commercial'' X-Server is WinaXe (http://www.labf.com/winaxe/).
I have used the evaluation version of this program and liked it. As of
this writing, it costs $100 for the ``Plus'' version which supports
secure SSH connections and $90 for the ``non-secure'' version. Of
course, you can obtain and install the evaluation version for free (and
with much less hassle than Cygwin), but that version will disable
itself after a period of time. Also, it requires that you restart the
server after an hour of continuous use.
For Macintosh, (I believe) XDarwin http://www.xdarwin.org is an
To transfer files to/from csci you'll need an sftp client. For
Windows I recommend FileZilla which is a free download and can be obtained
If you read the first part of this section with some level of understanding
you know how to connect to a Linux server (using ssh) and you also
know that once you've connected you have a choice between using a
command-line interface or a graphical interface. Allow me to summarize the
advantages and disadvantages of the two approaches:
|no additional software needed
||requires expensive (either money or
time) additional software
|very fast (if you know commands and
||will run slowly, especially when
accessing the server from off-campus
(because the GUI information has to
travel across the network)
|very time-consuming to become
proficient with the commands and
tools needed for assignments
||issuing commands and running
programs will be intuitive using
standard GUI widgets
Using the Command-Line Interface
This section describes how to perform various tasks via the command-line
Here are some file-manipulation commands you will likely want to use.
- lists files in a directory. There are many
options that can be supplied to modify the behavior of
ls. Here are some examples of using ls.
||lists all files in current directory
||modifies file listing to differentiate
between types of files (directories,
|lists all files in the subdirectory
c in the subdirectory programs in
your home directory
||shows all files, including hidden ones; files
with names that begin with a period are
designated ``hidden'' and are immune from
some file operations
||shows all files in the current directory
whose names end with cpp
||same as doing both -a and -l
- moves or renames a file. This command can be used
rename a file or to move it from one directory to
another. It should be noted that mv can be applied to
directories as well as files. Examples:
|mv old.txt new.dat
||renames file from old.txt
|mv myprogs/cool.cpp .
||moves file named cool.cpp
in the myprog directory into the
|mv myprogs oldprogs
||if we assume that myprogs is a
directory (as in the previous example) then
this would rename the directory to be oldprogs
- copies a file. This works pretty much the same
way as mv with two exceptions. First, the original
file is left intact. Secondly, cp doesn't copy
entire directories (unless you use the -r option).
- removes a file.
- changes mode (access permissions) for a file.
Every file and directory has read, write, and executable
permissions for three classifications of users: the user
(u), the group (g), and others (o).2 For example, a file can be set to be readable and
writeable, but not executable for the user/owner and
not readable, writeable, or executable for group members
or for anyone else. Likewise, you may want to allow
anyone to view a particular file, but not write to it,
etc. To view the current settings you can use the
ls -l command which will produce output similar
drwxrwxr-x 3 sergeant sergeant 1024 Aug 14 10:27 office52
-rw------- 1 sergeant sergeant 26907 Jul 30 1999 personal.xls
drwxrwxr-x 2 sergeant sergeant 1024 Jul 24 07:50 rpm
-rw-rw-r-- 1 sergeant webcache 28492 Aug 18 18:29 stats.ps
-rw-rw-rw- 1 sergeant sergeant 5373 Feb 5 2000 questions.tex
Each line contains information for a single file. The
first ten characters provide information about
permissions. The first character has a d if the
file is a directory and a - otherwise (usually).
The remaining nine characters specify the read (r),
write (w), and executable (x) permissions for user,
group, and others. The file named personal.xls
is readable and writeable by the user (sergeant)
and not available to anyone else. The file stats.ps
is available for reading and writing to the user
(sergeant) and the group (webcache), but
only readable to everyone else. You may notice that
both directories (office52 and rpm) have
executable permissions turned
on ... without those permissions a directory is
There are two main ways to invoke the chmod
command. Only the mnemonic method is explained here.
The command is followed by a request for new permissions
and lastly the filename(s) to which the new permissions
should be applied.
|chmod guo+rw public.txt
||makes the file
public.txt readable and writeable by anyone
|chmod go-rwx *cpp
||remove all types of access from group
or others for all files whose names end with cpp
- makes a new directory. Simply follow the
command with the desired directory name.
- removes a directory. The main thing to be aware
of here is that the directory must be empty before it can
be removed with rmdir.
- changes to a new working directory. Two notes of
interest: cd .. moves one level up the directory
tree. Also, cd with no directory name changes to
the user's home directory (the directory you are in when
you first log in).
- displays present working directory. Depending on
how your prompt is displayed you may not have a reminder
as to what directory your are currently working in. This
command will let you know where you are.
Here are some additional commands (that don't necessarily deal directly
with managing files) that you may find helpful:
- displays manual pages for any command. For
example, if you wanted to find out all of the
options available for the ls command you can type
- displays list of commands relevant to the
specified topic. Example: apropos clock displays
information about various commands dealing with a clock.
- finds files. This command has numerous options
that allow you to find a file based on all manner of
criteria. Example: find -name henry.txt will search
the current directory and all its subdirectories for a
file named henry.txt.
- searches files for given text. If you want to
find which files contain certain text then grep is
what you want. For example: grep Diana *.txt shows
all occurrences of ``Diana'' in all files in the current
directory whose names end with .txt.
- changes your password. NOTE: Use the
yppasswd command if using a lab computer.
- captures output to a file. This is especially
useful for capturing the output of an interactive program
(as is often requested by an instructor). The command
works as follows:
In this example all of the output generated by the ls
command and by the program compilation and by the program
that was executed are all sent to the file named myprog.out (as well as to the screen). The command
exit tells the script command to stop logging the
output to the specified file.
There are many fine text-based editors available on csci. The
two most widely used editors are vi and emacs. I know and
use vi (actually, vim: vi Improved) so that is what I document
here. Feel free to experiment with emacs (or other editors).
First, the bad news: vi has a steep learning curve. Plan on spending
quite a bit of time learning to use the editor before you attempt to
do something substantial with it.
Here are some resources that should help your transition to vi:
- Don't try to use vi to do anything useful until
you've gone through an introductory tutorial and you've taken
some time to play around with it. Then, and only then, should
you try to use it for an assignment.
Also, in the early stages don't try to use vi when you are
in a hurry. The idea is that you want to be proficient before
you add the stress of ``hurry'' to the stress of learning
- On csci there is a vi tutorial called
vimtutor. Spend time to go through that tutorial. You
may even want to go through it several times until you become
comfortable with the various commands.
- Quick Reference
- There is a two-page ``vi quick reference card''
written by Don Bindner available at
I can make copies available on request.
- On-Line References
- There are many on-line references and
all you need to find them is
Writing and compiling programs using a text-based interface in Linux
involves writing/editing the source code using an editor of your choice
following by compiling the program by issuing the appropriate command.
Many editors provide commands within them to allow compilation without
leaving the editor. I sometimes work with two windows open: one for
issuing compilation commands and one for editing the source code.
To compile Java programs use:
||compiles Java program found in myprog.java and, if successful, produces a class file named myprog.class
||runs a compiled Java program
For sending and receiving (text-based) email I use a client called mutt. I like it an use it because it is fast, configurable, and simple to
use. But, as with many text-based programs it may take a while to become
comfortable using it. To invoke this program simply type mutt at the
To print virtually any document I recommend that you use the a2ps
print formatter rather than sending your document straight to the printer.
To use a2ps to print a document named myprog.cpp issue the
a2ps --printer=jb105 myprog.java
If you can't figure out that the document will appear on the printer in
JB 105 then you'll need me to tell you that you need to change ``jb105'' to
``jb104'' to cause the page to print on the printer in JB 104.
You may find that while you prefer to do most tasks via a GUI, that some
tasks (such as sending email or printing documents) are quite simple when
invoked from the command-line. Feel free to consult various subsections
from section 2 as needed.
The irony of having an ssh connection through which you forward GUI
information is that the graphical programs have to be invoked from the
command line. To run any of the programs discussed in this section simply
type the name of the program at the command-line. I recommend that you
follow the command with an ampersand (&) which will cause the program to
be launched in the background and will leave your command-line open to
invoke other programs as well. For example to invoke the gedit
editor you could type: gedit&
To load a file managing utility (similar to right-clicking on the Windows
Start menu and selecting Explore ...) you can use nautilus.
If you only need an editor for creating source code you will want to read
the discussion in the following section before reading this recommendation.
For general text editing needs gedit works fine. This editor has a
simple interface but performs syntax highlighting for some programming
languages (including Java).
There are two main options for you to consider for writing programs via
a remote connection to a Linux server:
- use a full-fledged integrated development environment (IDE);
- use a scaled-back integrated development environment (IDE);
(try jgrasp or bluej)
- use a graphical text editor and compile from the command-line;
(try gedit along with compiler commands given in
The advantage of the IDE is that you may be generally familiar with that
style of program development. On the down side, it can be somewhat of a
pain to create a simple stand-alone program. Also, the hefty interface
may be exceptionally slow over a network. Lastly, if you have trouble
using it or understanding it, I will be of no help because I haven't ever
The advantages of using a graphical editor and invoking the compiler
manually are that it will work more quickly over the network and I will
be able to be of some assistance if things don't go well. Also, you don't
have to create an entire directory (folder) filled with various files just
to compile a program. On the down side you will need to learn to use
the text-based compiler commands.
A scaled-back IDE falls in the middle of the other two options in terms of
required network capacity and ease-of-use.
The thunderbird email client is a good choice for sending or reading
email in a graphical interface. Consult the Linux
for information about how
to set it up. Also, evolution is a good choice.
Any GUI program will provide a menu option for printing. Rather than
printing to the default printer you will want to specify an alternate
printer (assuming you want to print in one of the labs). The choices
for alternate printers should be obvious.
A Next Step
There are many on-line and in-print resources that provide
information on how to use Linux. LINUX: Rute User's Tutorial and
Exposition is a book that is available in print
and (for free) online (see
http://www.kefk.net/RUTE/). It is quite comprehensive and, among
other things, provides its own list of helpful resources.
Terry Sergeant email@example.com