For old commands, just edit .bash_history and delete whatever you want from inside.
For commands in the current session, just run this command before you exit:
unset HISTFILE
The $HISTFILE environment variable is the one which holds your commands and will flush to the file once you exit the session.
Source: http://www.kossboss.com/linux—bash-history-clearing
And it’s FREE! I wouldn’t have written a blog entry for something except if it was such an amazing one:
In brief, sometimes a conflict occurs between some firewalls and the TCP SACK. In my case, the upload was severely affected and reached upload speeds of a few kilobytes over a LAN!
The following command disables TCP SACK and fixes the slow upload on all Ethernet cards:
sudo sysctl -w net.ipv4.tcp_sack=0
To make it permanent, edit /etc/sysctl.conf and add this line
net.ipv4.tcp_sack = 0
Then run:
sudo sysctl -p
Enjoy the ultra super duper fast uploads! I can now upload at above 40 MB/sec!
Sources:
After it is moved to another host, since it is a sparse file, the qcow2 takes the full space, e.g. if it was dynamically set to 100GB, it will take 100GB, even if only 50 GB were actually used.
I could get back more than 20 GB from my Win7 VM (from a 50 GB file) using this:
sudo qemu-img convert -O qcow2 win7.qcow2 win7_small.qcow2
Enjoy!
Source: http://www.tuxfixer.com/how-to-shrink-openstack-qcow2-image-with-qemu-img/
In brief, you should NEVER trust your HDD before handing it over to someone else!
The solution to this would be either wipe the whole HDD or at least wipe the files/folders that you need to keep out of reach.
There are two quick ways to do this on Ubuntu; shred and wipe. I prefer wipe because it can accept folders as well.
The point is to fill the place of your data with random bits multiple times, as follows:
r: for recursive
q: for quick mode, with only 4 iterations of random data.
Enjoy!
Note: This process is very time-consuming, even in quick mode, depending on how large your data is, and how fast the HDD you are wiping is.
Source: https://askubuntu.com/questions/57572/how-to-delete-files-in-secure-manner
Just Some Techie Notes! 