ServerBuddies Support Blog

How to install missing perl modules.

What is CPAN?

CPAN is the Comprehensive Perl Archive Network, a large collection of Perl software and documentation. You can begin exploring from either http://www.cpan.org/, http://www.perl.com/CPAN/ or any of the mirrors listed at http://www.cpan.org/SITES.html.

Note that CPAN is also the name of a Perl module, CPAN.pm, which is used to download and install Perl software from the CPAN archive. This FAQ covers only a little about the CPAN module and you may find the documentation for it by using perldoc CPAN via the command line or on the web at http://search.cpan.org/dist/CPAN/lib/CPAN.pm

Cpan is the easiest method to install new perl modules.

perl -e shell -MCPAN
install Bundle::DBD::mysql

Tags: How, install, missing, Modules, Perl

hdparm provides a command line interface to various kernel interfaces supported by the Linux SATA/PATA/SAS “libata” subsystem and the older IDE driver subsystem.

-T Perform timings of cache reads for benchmark and comparison purposes. For meaningful results, this operation should be repeated 2-3 times on an otherwise inactive system (no other active processes) with at least a couple of megabytes of free memory. This displays the speed of reading directly from the
Linux buffer cache without disk access. This measurement is essentially an indication of the throughput of the processor, cache, and memory of the system under test.

-t Perform timings of device reads for benchmark and comparison purposes. For meaningful results, this operation should be repeated 2-3 times on an otherwise inactive system (no other active processes) with at least a couple of megabytes of free memory. This displays the speed of reading through the buffer cache to the disk without any prior caching of data. This measurement is an indication of how fast the drive can sustain sequential data reads under Linux, without any filesystem overhead. To ensure accurate measurements, the buffer cache is flushed during the processing of -t using the BLKFLSBUF ioctl.

Tags: device, hdparm, Parameters, SATA/IDE

SSH Public key authentication

SSH Public key authentication works as follows:

The scheme is based on public-key cryptography, using cryptosystems where encryption and decryption are done using separate keys, and it is unfeasible to derive the decryption key from the encryption key. The idea is that each user creates a public/private key pair for authentication purposes.

The server knows the public key, and only the user knows the private key. ssh implements public key authentication protocol automatically, using either the RSA or DSA algorithms. Protocol 1 is restricted to using only RSA keys, but protocol 2 may use either. The HISTORY section of ssl(8) contains a brief discussion of the two algorithms.

The file ~/.ssh/authorized_keys lists the public keys that are permitted for logging in. When the user logs in, the ssh program tells the server which key pair it would like to use for authentication. The client proves that it has access to the private key and the server checks that the corresponding public key is authorized to accept the account.

The user creates his/her key pair by running ssh-keygen(1). This stores the private key in ~/.ssh/identity (protocol 1), ~/.ssh/id_dsa (protocol 2 DSA), or ~/.ssh/id_rsa (protocol 2 RSA) and stores the public key in ~/.ssh/identity.pub (protocol 1), ~/.ssh/id_dsa.pub (protocol 2 DSA), or ~/.ssh/id_rsa.pub (protocol 2 RSA) in the users home directory.

The user should then copy the public key to ~/.ssh/authorized_keys in his/her home directory on the remote machine. The authorized_keys file corresponds to the conventional ~/.rhosts file, and has one key per line, though the lines can be very long. After this, the user can log in without giving the password.

The most convenient way to use public key authentication may be with an authentication agent. See ssh-agent(1) for more information.

Tags: authentication, key, Public, SSH

The OpenSSH SSH client supports SSH protocols 1 and 2. Protocol 2 is the default, with ssh falling back to protocol 1 if it detects protocol 2 is unsupported. These settings may be altered using the Protocol option in ssh_config(5)

-v Verbose mode. Causes ssh to print debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems.

Multiple -v options increase the verbosity. The maximum is 3.

Example:

Tags: debugging, SSH, tips

How To Identify Major and Minor Number For Block Devices

How to identify major and minor device number?

Now, if you want to know the major and minor number of these devices, cd to /dev directory and do ls -l as shown below, which will show both major and minor number

[Note: Major for /dev/sda1 is 8 and minor is 2]

The major numbers for SCSI and IDE doesn’t change and has the following hard-coded value.

Tags: Block Devices, Major, Minor, Number