Bash Functions

A fork bomb is really just a bash function, below is an example of a bash function

helloworld() {
echo hello world
};

A fork bomb would be

:(){
 :|:&
};:

Now to explain.
:(){ - Creates the function
:|: - Next it call itself using recursion and pipes the output to another call of the function
& - Puts the function call in the background so child cannot die
}; - Terminate the function
: - Call (run) the function

If you would like a more human readable fork bomb it would be as follows

forkbomb(){
forkbomb | forkbomb &
}; forkbomb

Preventing Fork Bombs

We can prevent users from running fork bombs by limiting the amount of processes they are allowed to run.
We can achive this using /etc/security/limits.conf

To get started open /etc/security/limits.conf

nano /etc/security/limits.conf

In my example I want to limit the user john to 300 processes and any users in the group of students to 250 processes. For this I would put the following into my config file

john hard nproc 300
@students hard nproc 250

Please keep in mind that KDE and Gnome desktop system can lanuch many processes.

1. Firstly remove gnome-audio

   sudo apt-get remove --purge gnome-audio

2. Remove all your old users gconf data related to system sounds

   sudo rm -rf /home/*/.gconf/desktop/gnome/sound

3. Install some needed packages

   sudo apt-get install libcanberra-gtk-module libcanberra-gtk0 libcanberra0 gnome-session-canberra build-essential fakeroot dpkg-dev intltool debhelper

4. Grab the source for freedesktop sound theme from git.debian.org

   wget -O freedesktop-sound-theme.tgz 'http://git.debian.org/?p=collab-maint/freedesktop-sound-theme.git;a=snapshot;h=c6773c0c08eeaab03c466dc015d36809dff537bf;sf=tgz'

5. Unpack and apply some small fixes

   tar xzf freedesktop-sound-theme.tgz
   cd freedesktop-sound-theme/debian
   sed -e 's:touch build:./configure --prefix=/usr \&\& $(MAKE) \&\& &:' rules > tmp; cp tmp rules
   sed -e 's:\*:&.ogg:' freedesktop-sound-theme.install > tmp; cp tmp freedesktop-sound-theme.install
   rm tmp
   cd ../

6. Build and install the package

   sudo dpkg-buildpackage -rfakeroot
   cd ../
   dpkg -i freedesktop-sound-theme_0.2-1_i386.deb

7. Invoke gnome-sound-property and configure 'system sound'

   gnome-sound-property
   then you can select 'system sound' tab

8. Finally reboot your system and you should be good to go

First your going to need to install IPTables:
Gentoo: emerge iptables   (Must be  Root to use/install iptables)
Ubuntu/Debian: sudo apt-get install iptables

Then edit your .bashrc file and add the following

alias blockedips="iptables -L"
alias blockip="iptables -I INPUT -j DROP -s "
alias unblockip="iptables -D INPUT -j DROP -s "

Reload your .bashrc by running source .bashrc and you should then be able to run the commands below

blockedips - Will Show all Blocked hosts
blockip IP-HERE - Will Block that ip
unblockip IP-HERE - Unblocks that ip

Copying to remote machines

To copy a file to a remote machine run the following

scp ~/file/to/be/transfered username@hostname:~/destinationfolder

If you want to copy a directory you would use -r which would look like this

scp -r  /folder/to/be/transfered username@hostname:/path/to/destination

and if you want to specify a SSH port use -P which would look like this

scp -P port-here /file/to/be/transfered username@hostname:/path/to/destination

Grabbing from remote machines

To grab a file from a remote machine you would run the following

scp username@hostname:~/path/to/file/you/want /path/where/you/want/to/save/the/file

If you wanted a folder you would use -r which would look like this

scp -r username@hostname:~/path/to/folder/you/want /path/where/you/want/to/save/the/folder

and if you wanted to specify a SSH port use -P which would look like this

scp -P port-here username@hostname:~/path/to/file/you/want /path/to/destination

Mounting folders over SSH

Using SSHFS we can mount folders over ssh. To get started you'll need to installl sshfs

apt-get install sshfs

Create a dir to mount the files too and give your user ownership over it

mkdir /media/sshmount
chown username /media/sshmount

Then add your user to fuse group

adduser username fuse

You should be then able to mount using the following command

sshfs username@hostname:/path/to/folder/you/want/to/mount /media/sshmount

For Windows Users

If your on windows and you want to send or grab files over ssh you can using pscp
To send a file you would run the following

pscp C:\file\to\be\transfered username@hostname:/path/to/destination

To grab a file you would run the following

pscp username@hostname:~/path/to/file/you/want C:\path\where\you\want\the\file\saved

When using pscp the -r switch will work for folders and -P will also work for port