toucheatout  2006-08-07 11:53  Linux  

There are good tools to very closely evaluate a disk or disk array performance. This is especially critical for remotely mounted filesystems, where performance tweaks can turn a shame into a very reasonable and efficient network attached storage.
Bear in mind that it is difficult to take into account the multitude of requests when testing alone, and thoroughly tested system can behave very differently under a load from different sources.

Testing Writes

Replace the bs (as Block Size) by the setting you want to test, then ajust the count to create a file of the size you chose. Try to make it quite (2x) bigger than memory on the server if you are to test reading afterwards. /dev/zero is a good source of quickly grabbed bits...

  toucheatout  2006-05-19 19:09  Linux  

Cryptography, encryption, digital signatures...

Nowadays encryption and digital signature are two cryptographic applications that are bound to be more and more widely used as a replacement of safes and signatures for digital content. While the principles are used since quite some time in protocols like SSH or other VPNs for network trafic and PGP for emails, their use is not as widespread as it "should". We'll show here how to create and use a pair of keys suitable for the use with GnuPG, the open implementation of PGP.

A word on security

The keys that we will be generating can be used under certain legislation as a proof as strong as physical evidence, given the robustness of the algorithm. Given the time/computing power needed to break a GPG keypair, only governemental agencies can afford, so... Pay good attention to keep the private key absolutely secured. Indeed if compromised, the keypair becomes useless for encryption and anyone with it can digitally sign documents with your signature (and it will just look as good as if you made it...).

Creating the keypair and getting the cryptographic infrastructure right

Creation of the keypair

This is simply made with gpg --gen-key. This will ask you various questions about the keypair itself (key size, algorithm, expiration info), and personal info associated with the key. The defaults are usually sensible for the keypair parameters/.
Once created, the keys have to be somewhat exported so that people can sue them. It also would be good that the keys get signed by well-known persons (at least those that you intend to communicate with). Likewise, keys from your peers have to get known to the system (i.e. import them).

Exporting your (public, of course) key

gpg --export [keyID].

Exports all keys if keyId not present. Redirect the output or use the -o switch to indicate an output file.

Importing your peers' keys

When you want to add public keys from your peers, as you could have guessed, use the command:
gpg --import < key_file

Build your web of trust

So we can sign things now... put a mark that you in person approve of digital stuff. The other way, people can use you public key to encrypt messages only issued for you.

  toucheatout  2006-05-19 10:32  Linux  

Generate your pair of keys

ssh-keygen -t rsa
should simply do the trick and generate
~/.ssh/id_rsa and ~/.ssh/id_rsa.pub
that is a keypair suitable for ssh version 2. When prompted for a passphrase, leave it blank (just hit return).
The passphrase is skipped as the only critical piece of information is the private key (~/.ssh/id_rsa), that is mode 0700 in a 0700 directory so it should be fine. And the actual aim is to get instantaneous though secure login, not input a password anymore.

To create a stronger key than the default (1024 bits), use the -b switch (argument 2048, resp. 4096, even down - min 512).

  toucheatout  2006-03-26 18:52  Linux  

Choose your religion

Linux comes in a variety of flavors. It may very well end up the same core tools, the same linux kernel, it will have different default level of control, different administration tools, different package management systems and different filesystem layout. Choosing one's distro doesn't really matters in the end, yet each represents a certain state o find on how to organize the architecture.

Check out the subcategories for specific information.