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tutorial - USB Modem Configuration

Follow the steps mentioned below to configure internet connection using USB modem

1) Insert your usb modem and observe your /var/log/messages log file, you should see something like

Dec 11 16:44:56 poison kernel: ohci_hcd 0000:00:13.0: wakeup
Dec 11 16:44:56 poison kernel: usb 1-3: new full speed USB device using ohci_hcd and address 2
Dec 11 16:44:56 poison kernel: usb 1-3: new device found, idVendor=1004, idProduct=6000
Dec 11 16:44:56 poison kernel: usb 1-3: new device strings: Mfr=1, Product=2, SerialNumber=3
Dec 11 16:44:56 poison kernel: usb 1-3: Product: Qualcomm CDMA Technologies MSM
Dec 11 16:44:56 poison kernel: usb 1-3: Manufacturer: LG CDMA USB Modem
Dec 11 16:44:56 poison kernel: usb 1-3: SerialNumber: Serial Number
Dec 11 16:44:56 poison kernel: usb 1-3: configuration #1 chosen from 1 choice
Dec 11 16:44:57 poison kernel: cdc_acm 1-3:1.0: ttyACM0: USB ACM device
Dec 11 16:44:57 poison kernel: usbcore: registered new driver cdc_acm
Dec 11 16:44:57 poison kernel: drivers/usb/class/cdc-acm.c: v0.25:USB Abstract Control Model driver for USB modems and ISDN adapters

Here we are interested in knowing the port on which modem is connected, which is ttyACM0

2) Copy and past the following lines into your /etc/wvdial.conf

[Dialer Defaults]
Modem = /dev/ttyACM0
Baud = 57600
Init1 = AT+CRM=1
Phone = 777
Username = internet
Password = internet
Stupid Mode = 1
Compuserve = 0
Idle Seconds = 30

3) Run the following command to update any missing parameter in /etc/wvdial.conf file

poison:/etc # wvdialconf update

4) Run the following command to start the internet connection

poison:/etc # wvdial

I have tested this on Ferdora and Suse Linux and I believe that it should also work for you all.

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source:http://linuxpoison.blogspot.com/2007/12/13578175808369.html

tutorial - HowTO- Round Robin DNS

In this case we will take an example of a webservers

To use round robin, each web server must have its own public IP address. A common scenario is to use network address translation and port forwarding at the firewall to assign each web server a public IP address while internally using a private address.

This example from the DNS zone definition for foo.com assigns the same name to each of the three web servers, but uses different IP addresses for each:

;
; Domain database for foo.com
;
foo.com. IN SOA ns1.foo.com. hostmaster.foo.com. (
2006032801 ; serial
10800 ; refresh
3600 ; retry
86400 ; expire
86400 ; default_ttl
)
;
; Name servers
;
foo.com. IN NS ns1.foo.com.
foo.com. IN NS ns2.foo.com.
;
; Web servers
; (private IPs shown, but public IPs are required)
;
www IN A 10.1.1.11
www IN A 10.1.1.12
www IN A 10.1.1.13

When DNS gets a request to resolve the name www.foo.com, it will return one IP address, then a different address for the next request and so on. Theoretically, each web server will get one third of the web traffic. Due to DNS caching and because some requests may use more resources that others, the load will not be shared equally. However, over time it will come close.

This is a very good example of Load balancing using DNS server (Round Robin)

source:http://linuxpoison.blogspot.com/2007/12/13578175807025.html

tutorial - What is Segmentation fault

One of the most common problems when making software is errors like “Segmentation fault“, also called SegFault. Here is what a SegFault is.

Virtual memory in a computer can be created in 2 ways: pages or segments. Paging means that the memory is divided in pages of equal size, containing words of memory in it. Segmentation means that every process has a segment of memory of needed size, with gaps of empty memory blocks between the segments.

The operating system knows the upper limit of every segment, and every segment begins at a virtual address. When a program accesses a memory block, it calls a virtual address that the Memory Management Unit (MMU) maps to a real address. If the operating system sees that the requested address doesn’t match any valid address in the segment, it will send a signal to the process terminating it. SegFaults are the direct result of a memory error. The program has a bad pointer, a memory leak or any kind of error that makes it access the wrong memory address.

source:http://linuxpoison.blogspot.com/2007/12/135781758015953.html

tutorial - Allow normal users to mount drives

By default, Linux does not allow users to mount drives. Only root can do this

With a special command in the /etc/fstab file, you can change that. This is a typical line for the /dev/hda2 drive in /etc/fstab:

/dev/hda2 /mnt ext3 noauto,user 1 1

The keyword user allows any user to mount the drive into /mnt.

source:http://linuxpoison.blogspot.com/2007/12/135781758015581.html

tutorial - Quick and dirty configuration of NFS

NFS Consists of the following:

/etc/exports –> /etc/exports contains all the NFS shares

/usr/sbin/exportfs -r
#exportfs -r is used to synchronize nfsd in memory with the /etc/exports file
#Use exportfs -v to see which shares nfsd is currently exporting

/etc/rc.d/init.d/nfslock - which has 2 parts
/sbin/rpc.lockd
/sbin/rpc.statd

/etc/rc.d/init.d/nfs - which has 3 parts
/usr/sbin/rpc.rquotad
/usr/sbin/rpc.mountd
/usr/sbin/rpc.nfsd

At bare minimum you need to have portmap (or portmapper), mountd (or rpc.mountd), and nfsd (or rpc.nfsd) running; otherwise NFS isn’t running.

#Sample nfs /etc/exports file:
/home/ftp/pub (ro,insecure,all_squash)
/home/ftp/pub adminsvr(rw,insecure,all_squash)

#Above we have two entries, one for everyone, and one
for the adminsvr machine.

source:http://linuxpoison.blogspot.com/2007/12/13578175808775.html

tutorial - Get access to Linux files from Windows

There are a number of evident merits of the program, which you should know. First of all, DiskInternals Linux Reader is absolutely free. Secondly, the program provides for read-only access and does not allow you to make records in Ext2/Ext3 file system partitions. This guarantees that the interference in an alterative file system will not affect the work of Linux later. Apart from this, it is necessary to note, that it gives you an opportunity to use common Windows Explorer for extracting data. A preview option for pictures is one more pleasant point, which is worth mentioning.

While saving, it ignores file security policies. It means that it is possible to access absolutely any file on a Linux disk from Windows. The program can create and open images of Ext2/Ext3 disks.”

Download LinuxReader

source:http://linuxpoison.blogspot.com/2008/01/135781758014544.html

tutorial - VSFTPD - limit the number of simultaneous connections for a single IP address

By default VSFTPD allows unlimited connection from the same client IP address.

1: Open vsftpd.conf file

Use text editor such as vi to edit /etc/vsftpd.conf or /etc/vsftpd/vsftpd.conf file:
# vi vsftpd.conf

2: Setup limitation

Set up the max_per_ip=4 (this will limit simultaneous connection to 4 number only)
max_per_ip=4

3: Restart vsftpd

# /etc/init.d/vsftpd restart

source:http://linuxpoison.blogspot.com/2008/01/13578175808905.html

tutorial - KDE 4 Default Wallpaper

The Oxygen team is happy to present the final selection of 15 wallpapers that will be released with KDE 4.0. It took longer than expected to manage the contest due to the large number of entries (around 2000), but it was our first time organising such a contest. Read on for details of the winning entries.

source:http://linuxpoison.blogspot.com/2008/01/13578175806062.html

tutorial - Mount remote windows partition (windows share) under Linux

Use the mount command to mount remote windows partition or windows share under Linux as follows:

1) Make sure you have windows username and password to access share name
2) Login to Linux as a root user (or use su command)
3) Create the required mount point:
# mkdir -p /mnt/ntserver

4) Use the mount command as follows:
# mount -t smbfs -o username=nikesh,password=abc //ntserver/download /mnt/ntserver

source:http://linuxpoison.blogspot.com/2008/01/135781758013179.html

tutorial - Apache - limit access to certain directories based on IP address

You can do this completely from /etc/httpd/conf/httpd.conf which are shown below for multiple IP addresses. Note that all 3 setting are the same.

10.0.0.0/255.0.0.0
10.0.0.0/8
10

However, the following is different

10.0.0.0/24 only allows 10.0.0.1 to 10.0.0.254

Some complete settings in /etc/httpd/conf/httpd.conf

Order allow,deny
Allow from 10.0.0.0/8 # All 10.
Allow from 192.168.0.0/16 # All 192.168
Allow from 127 # All 127.

Don’t forget to reload httpd with the following command.

$ /etc/init.d/httpd reload

source:http://linuxpoison.blogspot.com/2008/01/13578175808768.html

tutorial - Defragmentation in Linux?

Sander Marechal published at LXer interesting observations on file defragmentation that is would be needed in Linux:

"I still wondered how on earth it was possible the 100k+ files in Gentoo’s portage system - updated every time I synchronize the portage tree - didn't fragment my filesystem. Or was my filesystem fragmented and did I not know? Only recently, I found a script that is actually able to put numbers to all this gut-feelings, and the results were quite surprising in my opinion."

Result: to achieve notable fragmentation level it’s necessary to do utmost. File fragmentation mainly happens in filesystems that contain large files. Pretty interesting.

Full article is here, as well as testing script, also you're welcome to read LXer discussion on this. Script for defragmentation is available at this page.

source:http://linuxpoison.blogspot.com/2008/01/135781758015880.html

tutorial - Linux related e-books - Free

Free Linux related e-books. E-books:

source:http://linuxpoison.blogspot.com/2008/01/13578175805097.html

source:http://linuxpoison.blogspot.com/2008/01/13578175804900.html

tutorial - Update Dell laptop BIOS with Ubuntu

Good news for Dell laptops owners: latest BIOS images can be loaded with Ubuntu, Fedora or CentOS! It was announced at official Direct2Dell blog by Matt Domsch. In a nutshell to get new BIOS installed while you're running Ubuntu 7.04 Feisty, 7.10 Gutsy, or Hardy just enable Universe repository in sources.list (System -> Administration -> Software Sources) and run under root (sudo -s):

wget -q -O - http://linux.dell.com/repo/firmware/bootstrap.cgi | bash aptitude install firmware-addon-dell aptitude install $(bootstrap_firmware -a) update_firmware

The first command enables Dell’s Ubuntu repository as well as downloads and installs GPG key for this repository. As you might guess, restart is needed after last command is done (keep fingers crossed)

Please note that detailed instructions on how to update BIOS with Ubuntu (or other Linux distro) and firmware-tools developed by Dell are here:

"We are releasing this project in the hopes of moving the industry towards a more scalable and friendly way to update BIOS and Firmware for systems."

Respect to Dell and it’s Linux engineers!

source:http://linuxpoison.blogspot.com/2008/01/135781758015128.html