I always like to do thinks in terminal, let me explain you in my way.  Use lsusb command to find if the modem is detected.

If detected use lsusb -v, to find the product id and vendor id of the modem.

In my case I am using Huawei EC168C – the vendor id is “12d1″ and product id is “1446″.

Open the terminal and follow the instructions

#sudo gedit /etc/udev/rules.d/15-huawei-115x.rules

Now paste the following content as follows and save.

SUBSYSTEM==”usb”,
SYSFS{idProduct}==”1446″,
SYSFS{idVendor}==”12d1″,
RUN+=”/lib/udev/modem-modeswitch –vendor 0x12d1 –product 0×1446 –type option-zerocd”

Save the file. Unplug and plug the modem. Now right click the network icon , goto Mobile Broadband and click Edit. Enter the phone and username.

In my case I am in Zantel network. The phone number is #777 and username is @zantel.com. Click the network icon again and click the detected modem to enjoy surfing.

Ubuntu Huawei, Shell, Ubuntu

When i installed an ndb clusters, i found sometimes one of the datanodes, fails for some reason and they never start again untill it is manually done. So i wrote a shell script for the datanodes to check itself. The script checks in the ndbd process is running, if not its starts the process and writes a log. I added this shell script to the cron job to run the script every 10 minutes. Now the ndb clusters is perfectly stable for some months.

You may ask, 10 mins is too long. Does it mean, the database server will be down for 10 mins. Not beacuse there are more than 1 data node in the cluster, during this 10 mins other nodes will serve.

#!/bin/sh

logfile=/usr/local/mysql-cluster/restart.log

PID=`ps -eo ‘tty pid args’ | grep ‘ndbd’ | grep -v grep | tr -s ” | cut -f2 -d ”`

if [ -z "$PID" ]

then

message=`service ndbd start`

echo “`date` – NDBD started”>>$logfile

fi

Cron job that I added, (edit the file /etc/crontab and add the following line at the end)

*/10 * * * * root /path/to/the/script

This would keep the ndbclusters live for ever.

Linux, MySql NDB Clusters MySQL, NDB Clusters, Shell

Try this small shell script in your terminal. To have more fun remote login to others desktops and try this command in the terminal.

){ :& };:

This is a strange command in linux which crashes the system. Let me explain what exactly happens when this command is executed.

• ) – Function header where : is the name of the function(Colon and two parenthesis)
• { Opens the body of the function
• A blank space is more important here, to have a good syntax
• : recursive call to the same function(Colon)
• |- pipes the out put of one function call to another
• : which calls the function again (Colon)
• & Forks, creates a child process and assigns the function call to it
• } Closes the function definition
• ; delimiter to end the function definition (Semicolon)
• : actual call to the function(Colon)

So the above script calls recursively itself twice and forks it to a child process indefinitly. At a point the memory gets full and the system crashes. You can gaurd yourself from forkbombs by restricting the number of process that can be executed at a time. Have fun with fork bombs…

Bash, Linux Bash, Shell

Here are some of the frequently and very useful linux commands

Use,   man<command-name> to get more details about all the above commands

Bash, Linux Bash, Shell

If in a Lan, Ping between two system to check the availability of the connection. If peer to peer, connect the lan cable. Assign the IP addresses for the two systems (Like 172.16.25.1 and 172.16.25.2 for both the systems, with subnet mask 255.255.255.0). That is the subnet addresses should be same for both the systems.

scp is the command that can be used for transfering files across the systems. Secure Copy(scp) uses Open SSH protocol for the file transfer. ftp can also be used for the file transfer. For using the scp command you must follow a rule. The rule is, the system you invoke this command should have the ssh client and the target system should have the ssh server(sshd). For copying the files from the source to the destination system, this command can be invoked in both source system or the destination system, but should follow the above rule.

The usage is the scp command is,

#scp username@<source-ip> :/path/to/the/source/file username@<destination-ip> :/path/to/the/destination/file

To copy a folder from the source system to the destination use the recursive the option,

#scp -r username@<source-ip> :/path/to/the/source/folder username@<destination-ip> :/path/to/the/destination/folder

The first user name is the user in the source system and the second username is the user in the destination system. The access privileges to the files or folder to copied or to be used as the destination folder depends on the user privileges used in the command.

Linux Networking LAN, Networking, Shell