CodeMarvels – Page 20 – A Coder’s Notebook.

Skip Authorization on MySQL DB

Posted on December 28, 2012 by Sreekumar Kj

To skip authorizations and login without password to MySql server,

sudo vi /etc/mysql/my.cnf
Add the line skip-grant-tables after the linewhich reads skip-external-locking.
1. Optionally comment the line bind-address = 127.0.0.1 if the db has to be accessed from external devices via TCP.
Save and quit vim.
restart mysql server ( sudo /etc/init.d/mysql restart in ubuntu)

Chat/Text messaging from commandline on Linux

Posted on November 16, 2012 by Sreekumar Kj

Want to urgently copy a text message from one pc to another, or have a short conversation with a peer on another pc ? here’s how –

@ PC1: nc -l [port-number to listen, without brackets of course]

@PC2: nc [IP of PC1] [port-number above]

Now type any text on pc2 – it should be visible on pc1, and vice versa.

notes/technology

How to find the latest queries run in MySQL

Posted on September 24, 2012 by Sreekumar Kj

Run the following queries –

SET GLOBAL log_output = 'TABLE';
SET GLOBAL general_log = 'ON';

After the latest 100 queries executed after this is done can be found by running the query –

SELECT * FROM mysql.general_log where argument like ‘%[queryPiece]%’ order by event_time desc LIMIT 0,100

notes/technology

Activate password authentication on Ubuntu VMs on Amazon EC2

Posted on September 7, 2012 by Sreekumar Kj

ssh -i [path to private-key-file] [target IP]

# In the host shell

sudo adduser [username]     # Add a new user; this command also prompts for setting the password

sudo adduser admin            # Add this user to the admin group (to sudoers)

sudo vi /etc/ssh/sshd_config

# In the above file set "PasswordAuthentication" to "yes".

sudo reload ssh

The VM should now be ready for password based ssh authentication.

notes/technology

Extract .gz file using gzip without deleting the original file

Posted on September 3, 2012 by Sreekumar Kj

Extract the .gz file to standard output (option -c) and pipe this to target file.

# example
<pre><code>gzip -c inputfile.gz > outputfile</code></pre>

notes/technology

Find the files contained in/provided by an Ubuntu/Debian package

Posted on August 28, 2012 by Sreekumar Kj

On console, run

dpkg -L [package name]

notes/technology

Find the list of installed packages in Ubuntu/Debian

Posted on August 28, 2012 by Sreekumar Kj

To find the list of installed packages on ubuntu/debian, on console run

<pre>dpkg --get-selections</pre>

To find if a specific package is installed –

<pre>dpkg --get-selections|grep <packagename></pre>

notes/technology

Temporarily enable SSH password authentication on RHEL/Centos VMs.

Posted on August 17, 2012 by Sreekumar Kj

To enable password based authentication on RHEL/Centos machines, login as root to the target host. ( sudo the commands below if you are not logging in as root)

1. Create the password authenticated user if not already created –

On console run : adduser [username]
Set a password for the new user: passwd [username]

2. Add the user to sudoers and enable remote login –

On console run: visudo
In the file opened for editing, comment out the line – “Defaults requiretty“
Add the line “[username] ALL=(ALL) ALL” below the line “root ALL=(ALL) ALL“

3. Enable password authentication for SSH.

vi /etc/ssh/sshd_config
Replace the line “PasswordAuthentication no” with “PasswordAuthentication yes“. (Uncomment this line if commented.) Save and close this file.
/etc/init.d/sshd reload

4. To disable password authentication after use, in the above file replace “PasswordAuthentication yes” with “PasswordAuthentication no“; reload sshd as before.

notes/technology

Public key authentication not working on RHEL/CentOS

Posted on August 17, 2012 by Sreekumar Kj

Problem: SSH asks for password even after updating the .ssh/authorized_keys in target host with user’s public key.

Reason: A permission issue

Fix: Login with password, in console run

chmod -R 700 ~

Log out and try again. The public key login should work now.

notes/technology

Fix Vim editor on Ubuntu

Posted on June 11, 2012 by Sreekumar Kj

Problem: The arrow keys insert characters, no status message at the bottom etc.

Reason : The default Vim on Ubuntu is vim-tiny, a skeleton version.

Fix: Install the real stuff – sudo apt-get install vim

Note: vi = Visual, vim = Visual improved. And vim-tiny is vi compatible, kind of Jurassic.