Linux Blog

Creating executable of Shell Script

Many times it happen that shell scripts that we write contains sensitive information like password or some sort of keys or path to some sensitive files and if you running such script it become very easy for the normal user to have a look inside the script and get the sensitive information from the code.
There is a program called "shc" which can provide the protection from such cases that developer wants.

shc itself is not a compiler such as cc, it rather encodes and encrypts a shell script and generates C source code with the added expiration capability. It then uses the system compiler to compile a stripped binary which behaves exactly like the original script. Upon execution, the compiled binary will decrypt and execute the code with the shell -c option. Unfortunatelly, it will not give you any speed improvement as a real C program would.

shc's main purpose is to protect your shell scripts from modification or inspection. You can use it if you wish to distribute your scripts but don't want them to be easily readable by other people.

Download shc (here) and untar it:

tar -xzvf shc-X.X.tgz
cd shc-X.X/
make
make install

This will install the shc binary on your box.

Create a file called: script.sh and add the following contents for testing purpose

############################### script.sh ##############################
#!/bin/sh
echo "This is a test shell script by Nikesh"
############################### script.sh ##############################

Now run the command:
shc -f script.sh

The switch "-f" specifies the source script to encrypt. The above command will create two files: script.sh.x.c and script.sh.x. The encrypted shell script is: script.sh.x. Run that binary and see the output:

./script.sh.x
This is a test shell script by Nikesh
Now you can distibute the script.sh.x without any fear

You can also specify a time limit on the shell script so that it will no longer execute after a certain date (expire) and you can specify a custom message to echo back to the user.

shc -e 09/12/2008 -m "Licence expire, please contact author - Nikesh" -f script.sh
./script.sh.x
./script.sh.x has expired!
Licence expire, please contact author - Nikesh

Check out the man pages for more info on "shc".

Quick and Easy VNC Server setup

VNC, or Virtual Networked Computing, is a way of controlling a remote computer just as though you are sitting in front of it. In the Windows world it is also known as remote desktop but it's normally referred to as VNC in the Linux world. All that happens is that you connect using a VNC client to a remote computer running the VNC server, then an image of the remote desktop is transmitted to your local computer and you can see and control the desktop just as though you are there since all keyboard and mouse commands are sent from your client machine to the server.

Step:1: Installation
First check if you already have them installed on your system, open a terminal and type:
$ rpm -qa | grep vnc
vnc-server-4.1.2-9.el5
If you get an output something like this then you're all ready, if not you need to install them via yum.

Step 2 : Start the VNC server.
$ vncserver
......

New 'server:1 (user)' desktop is server:1

This will ask for password, you need to remember this password and need to provide it at the time of connecting to the server through VNC client.

Step 3 : Connecting from VNC client
From client run vncviewer (dont run remote desktop connection from winxp or win2003 .they are using different protocol.)

In server enter : server:1

enter password: **********

And you will see the screen with one terminal open because by default vnc starts twm desktop.

For getting your gnome desktop

Go to folder /user/.vnc/ (user home directory) and open file xstartup using vi editor and uncomment or add the following lines

unset SESSION_MANAGER

exec /etc/X11/xinit/xinitrc

Restart the vncserver and connect to it using vncviewer, you should now see your default desktop, something like ..

A script for managing file archives of various types

atool is a script for managing file archives of various types (tar, tar+gzip, zip etc).

The main command is aunpack which extracts files from an archive. Did you ever extract files from an archive, not checking whether the files were located in a subdirectory or in the top directory of the archive, resulting in files scattered all over the place? aunpack overcomes this problem by first extracting to a new directory. If there was only a single file in the archive, that file is moved to the original directory. aunpack also prevents local files from being overwritten by mistake.

The other commands provided are apack (to create archives), als (to list files in archives), and acat (to extract files to standard out). As atool invokes external programs to handle the archives, not all commands may be supported for a certain type of archives.

atool identifies archives by their file extension. Sometimes this is not possible - for instance rar archives usually have varying numeric file extensions. In those cases when atool can't identify the format, file is used instead. (atool can be configured not to use file.)

atool is written in Perl by Oskar Liljeblad and is free software (GNU General Public License ).

Download
The latest version of atool is 0.35.0, which was released on 2008-06-08:
Source code tarball
Debian package (all architectures)
RPM package (all architectures)

Building from source
To build all files, simply run: ./configure
The configure script accepts a few options - use the following command to show them: ./configure --help

Installation
Installing atool is a matter of copying the atool file to some appropriate directory for executable files, usually /usr/local/bin. After that, symbolic links for apack, aunpack, als and acat to atool should be created in the same directory. All this can be done automaticly by running: make install

Usage and Configuration
A list of options that atool accepts can be displayed by running atool with the --help option: atool --help
Please see the manual page for atool for full use and configuration information. This document can usually be viewed this way: man ./atool.1

Firewall for Ubuntu - Gufw

iptables is already a very powerful tool by itself, but it's syntax can get awkward at times and hard to figure out, so Ubuntu developers decided to make ufw ("The reason ufw was developed is that we wanted to create a server-level firewalling utility that was a little bit more for `human beings`."), which was to be simpler. Now, on the graphical side of things, Firestarer already existed. But why not make an even easier to use GUI for desktop `human beings`, powered by ufw? This is where Gufw comes in.

Gufw is an easy to use Ubuntu / Linux firewall, powered by ufw.

Gufw is an easy, intuitive, way to manage your Linux firewall. It supports common tasks such as allowing or blocking pre-configured, common p2p, or individual ports port(s), and many others! Gufw is powered by ufw , runs on Ubuntu, and anywhere else Python, GTK, and Ufw are available.

You can install it on ubuntu with this deb package: here

Creating Recycle Bin for Samba storage

I assume that you have successfully configure the samba server, if not, here is a quick and dirty samba configuration guide - here

Samba is mainly used to share the files between Linux and windows and many times it happens that user deletes the file from the samba server and later wants to get back deleted files which is not possible with the default configuration of samba server.

The best option is to have a "Recycle bin" for every users on the samba server.
Here is an example of modifying the home directories of your users in samba configuration file

[homes]
comment = Home Directory
valid users = %S
browsable = no
guest ok = no
read only = no
vfs object = recycle
recycle:repository = RecycleBin
recycle:keeptree = yes
recycle:exclude = *.tmp, *.bak

The “vfs object” line calls in the plug-in that enables recycle bin capability. On the other lines, you’re setting the name of the recycle bin directory, telling Samba to preserve the whole structure of any directories that a user may delete, and finally, telling it to not keep certain types of files.