In order to access USB drive under Linux you need to load special USB driver and support must be included in running Linux kernel. Try following command one by one to solve your problem:

Step # 1 : Make sure your external drive detected by system
Run dmesg command which print or control the kernel ring buffer:

# dmesg

OR

# dmesg | grep –i USB

Output:

SLPB PCI0 HUB0 USB0 USB1 USB2 USBE
usbcore: registered new driver usbfs
usbcore: registered new driver hub
USB Universal Host Controller Interface driver v2.3
uhci_hcd 0000:00:1d.0: new USB bus registered, assigned bus number 1
hub 1-0:1.0: USB hub found
uhci_hcd 0000:00:1d.1: new USB bus registered, assigned bus number 2
hub 2-0:1.0: USB hub found
uhci_hcd 0000:00:1d.2: new USB bus registered, assigned bus number 3
usb 1-2: new full speed USB device using uhci_hcd and address 2
hub 3-0:1.0: USB hub found

As you see USB support is included in kernel. You can also verify this with following command:

# lspci -v | grep HCI

Output:

0000:00:1d.0 USB Controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) USB UHCI Controller #1 (rev 02) (prog-if 00 [UHCI])
0000:00:1d.1 USB Controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) USB UHCI Controller #2 (rev 02) (prog-if 00 [UHCI])
0000:00:1d.2 USB Controller: Intel Corporation 82801DB/DBL/DBM (ICH4/ICH4-L/ICH4-M) USB UHCI Controller #3 (rev 02) (prog-if 00 [UHCI])
0000:00:1d.7 USB Controller: Intel Corporation 82801DB/DBM (ICH4/ICH4-M) USB2 EHCI Controller (rev 02) (prog-if 20 [EHCI])

Step # 2 : Load USB modules/driver
If you cannot see your external USB drive in above dmesg output then try to load usb-uhci and usb-ohci modules (driver):

# modprobe usb-uhci
# modprobe usb-ohci
# modprobe usb-storage

Now again run dmesg:

# dmesg

Output:

usb 4-1: new high speed USB device using ehci_hcd and address 3
scsi2 : SCSI emulation for USB Mass Storage devices
usb-storage: device found at 3
usb-storage: waiting for device to settle before scanning
Vendor: SAMSUNG   Model: SV4002H           Rev: 0811
Type:   Direct-Access                      ANSI SCSI revision: 00
SCSI device sdb: 78242976 512-byte hdwr sectors (40060 MB)
sdb: assuming drive cache: write through
SCSI device sdb: 78242976 512-byte hdwr sectors (40060 MB)
sdb: assuming drive cache: write through
sdb: sdb1
sd 2:0:0:0: Attached scsi disk sdb
usb-storage: device scan complete

Step 3 : Use external USB drive
As you see device sdb assigned to an external USB drive use mount command to mount drive:
List partitions on /dev/sdb:

# fdisk -l | grep sdb

Output:

Disk /dev/sda doesn't contain a valid partition table
Disk /dev/sdb: 40.0 GB, 40060403712 bytes
/dev/sdb1               1        4870    39118243+   c  W95 FAT32 (LBA)

Now mount partition:

# mount /dev/sdb1 /mnt

See also:

• Linux : How to use USB pen/flash stick
• Allow normal user to mount linux partitions, usb stick/pen device

Unlike other operating systems (Windows) each step of loading a Linux system easily understood.

The Boot Process

It is also easy to break.

1. The BIOS loads the Boot Sector (Grub) from Sector 0
2. The Grub (root line in grub.conf) points to the partition containing the kernel (Linux).
3. The kernel loads and initializes the devices and runs /sbin/init (process 1)
4. /sbin/init runs /etc/rc.d/rc.sysinit to initilize devices.
5. /sbin/init reads /etc/inittab
6. /etc/rc.d/rc.sysinit run all the scripts int the approach run level directory.

GRUB

Grub is the first step in the boot process and has the greatest Oh ---- factor. But it really doesn't have to be a big problem. You may not need to boot from a live CD to fix this. There are three main parts to boot step

• root
• kernel
• initrd

Try booting and editing each of these lines in GRUB. Purposely make mistakes to learn what errors are produced.

The TAB key will do auto completions when you are editing a GRUB options.

Rescure Mode

Using the first CD to boot into Rescue mode. You can then search for the root file system and mount it to the directory /mnt/sysimage.

  chroot /mnt/sysimage
 grub

Following this command you need to show grub where to read the grub configuration. If the drive type may have changed, maybe because you changed from IDE to SCSI disks you will need to do a --recheck. Then install grub with the install command.

  grub-install --recheck /dev/hda
 grub-install /dev/hda

Redhat will ask if you want to mount the root file system. If you say no you will need to mount the root file system your self. Here are the commands to do this with the VMware system.

  mkdir /mnt/root
 mkdir /mnt/root/boot
 mount /dev/md1 /mnt/root
 mount /dev/md0 /mnt/root/boot

Fixing INITRD Modules

If the kernel is missing or corrupt you will need to reload it from the install CD.

If the initrd file is missing you you can also reload it with the kernel.

Adding missing modules to initrd:

  rm -f /boot/initrd-2.6.20-1.2320.fc5.img
 mkinitrd --preload=xor --preload=raid456 /boot/initrd-2.6.20-1.2320.fc5.img
 2.6.20-1.2320.fc5

Manually changing initrd:

  mkdir /root/initrd-tmp
 cd /root/initrd-tmp
 cp -a /boot/initrd-2.6.20-1.2320.fc5.img ..
 mv ../initrd-2.6.20-1.2320.fc5.img ../initrd-2.6.20-1.2320.fc5.img.gz
 gunzip ../initrd-2.6.20-1.2320.fc5.img.gz
 cpio -i --make-directories < ../initrd-2.6.20-1.2320.fc5.img
 vi init
 find . -depth | cpio -o > ../initrd-2.6.20-1.2320.fc5.img
 cd ..
 rm -rf initrd-tmp
 gzip -9 initrd-2.6.20-1.2320.fc5.img
 mv initrd-2.6.20-1.2320.fc5.img.gz initrd-2.6.20-1.2320.fc5.img
 mv initrd-2.6.20-1.2320.fc5.img /boot

SYSINIT

INITTAB

The file /etc/inittab controls the runlevel the system boots into.

You can override this by added the runlevel you want to the end of the kernel line in GRUB.

id:3:initrdefault:

Changing the 3 in this line will change the default runlevel to the one you want.

Runlevels

Here are the runlevels and what they mean. You should know the by heart too.

• Run level 1 is single user
• Run level 2 is Multiuser without NFS
• Run level 3 is Full Multiuser
• Run level 4 is unused
• Run level 5 is X11 windows
• Run level 6 will reboot the system

/etc/inittab not only starts rc.sysinit it also starts processes that shouldn't die. One of these is the system console/s. It controls which run level the system automatically boots to. The directory /etc/sysconfig hold config files for process started at this level.

RC scripts are kept in /etc/rc.d. The program that run the RC scripts is rc.sysinit. These scripts are what is done when you change run level with the init command.

The fastest to set runlevel services is to use the command 'ntsysv and tell it the runlevels you want to set. For example, this will display and change runlevels 3 and 5.

  ntsysv --level 35

To turn on or off a RC script you can also use the command:

  chkconfig --level command on/off

The option --level sets the run level to be change for the command that is turned on or off. This can also be done with the GUI system-config-services.

  chkconfig --list

This command will list all the services and if they are on or off for each run level.

  chkconfig --add/--del command

This command will add or delete a new command from the RC start-up scripts.

After configuring a system like Apache it is easy to forget make it start at boot time. Don't forget to reboot you system before the test is over.

You can debug the RC process by booting into single user mode and running the RC scripts in the run level by hand. You can also bypass init by adding init=/bin/bash the kernel line in GRUB.

CLONING or RESTORING a System

THIS IS NOT NEEDED FOR THE TEST

Here are some of the issues if you are cloning or restoring a system by copy all the files into empty directories and then restoring the boot process. This process involves creating all the required root directories (/ /etc /usr /bin /var /opt /home) and coping all the files back into place with their ownership and permissions maintained. Directories that are not copied include /tmp /dev /proc /mnt. The directories that are not copied do need to be created.

• The partitions and/or e2 labels may not be the same. This will require changing /etc/fstab
• Some directories will/may not be copied. This may include /dev. In witch case mounting the root file system with the chroot command will leave you without any devices.
• Grub.conf (/etc/grub/grub.conf and menu.lst) may also need editing. Both the root and kernel lines may contain references to the wrong partitions.
• /etc/mtab needs to be edited to match the new disk. Partition numbers can change and sometimes the type, like from IDE to SCSI (hda to sda).

After booting into recover mode with the install CD. You will need to mount all of the file systems into their place under /mnt/sysimage. You can them mount the live proc and dev inplace with the command:

  mount -o bind /dev /mnt/sysimage/dev
 mount -o bind /proc /mnt/sysimage/proc

With the file systems in place you can use the chroot command to create the write environment for fixing the master boot record and Grub.

  chroot /mnt/sysimage

In this howto i will describe how to install subversion with TRAC. Subversion is an open source version control system alternative to CVS and TRAC an enhanced wiki and issue tracking system for software development projects which provides an interface to Subversion. I install it on CentOS 5.4 which is already running as Web Server. I will use sohailriaz.com source to be maintain by Subversion and TRAC to track all development.

1) Installation

To install subversion and trac on CentOS 5.4 we will use dag repositories as it has latest packages (rpms) available for said softwares.

Red Hat Enterprise Linux / CentOS 5 / i386:

rpm -Uhv http://apt.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.i386.rpm

Red Hat Enterprise Linux / CentOS 5 / x86_64:

rpm -Uhv http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS//rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

Now issue yum command to install subversion and trac with pre-requisites.

yum -y install subversion trac mod_dav_svn mod_python

where mod-dav_svn and mod_python are apache modules which will be use later on to access subversion and trac.

2) Configuring Subversion.

2.1) Creating directories for Subversion.

mkdir /var/www/svn/svnrepos

mkdir /var/www/svn/auth

2.2) User Authentication.

We will create a user to access SVN repositories

htpasswd -cb /var/www/svn/auth/svn.htpasswd svnuser1 passw0rd

Adding password for user svnuser1

2.3) Create Project Repository.

Now we will create a Project Repository. It can be user define name. I will choose site-sohailriaz.com name here for my Project Repository.

svnadmin create /var/www/svn/svnrepos/site-sohailriaz.com

svn mkdir file:///var/www/svn/svnrepos/site-sohailriaz.com/branches file:///var/www/svn/svnrepos/site-sohailriaz.com/tags file:///var/www/svn/svnrepos/site-sohailriaz.com/trunk -m “Creating directories for initial import”

Committed revision 1.

Change ownership and group member to apache (default user for web server)

chown -R apache:apache /var/www/svn/svnrepos/site-sohailriaz.com/

Generate configuration for svn to view from website.

vi /etc/httpd/conf.d/svn.conf

<Location /svn>

DAV svn

SVNListParentPath on

SVNParentPath /var/www/svn/svnrepos/

AuthType Basic

AuthName “SohailRiaz.com Site Repository”

AuthUserFile /var/www/svn/auth/svn.htpasswd

Require valid-user

</Location>

Start service to take the changes.

/etc/init.d/httpd restart

Now browse your site to see the SVN repository.

http://www.sohailriaz.com/svn/

It will ask the user/pass you created initially and after successful login you will see your repositories.

2.4) SVN Import for site files.

We will use svn import to import files from our site to repository to maintain the code.

svn import /home/sohail/public_html/ http://www.sohailriaz.com/svn/site-sohailriaz.com/trunk/

Authentication realm: SohailRiaz.com Site Repository

Password for ‘root’ : <enter root password>

Authentication realm: SohailRiaz.com Site Repository

Username : svnuser1

Password : passw0rd

Now browse your site and see the trunk folder, you will see your code listed there.

2.5) Branches

If you need to have multiple branches for your site then that is relatively very easy within subversion. All you need to copy from trunk to branches folder with user define name to recognized.

svn copy http://www.sohailriaz.com/svn/site-sohailriaz.com/trunk/ http://www.sohailriaz.com/svn/site-sohailriaz.com/branches/site-sohailriaz.com-branch-1 -m “1st Branch for Site SohailRiaz.com”

3) Configure Trac.

First configure trac instance using trac-admin command for svn repository site-sohailriaz.com

trac-admin /var/www/trac/site-sohailriaz.com initenv

Creating a new Trac environment at /var/www/trac/site-sohailriaz.com

Trac will first ask a few questions about your environment

in order to initalize and prepare the project database.

Please enter the name of your project.

This name will be used in page titles and descriptions.

Project Name [My Project]> Site SohailRiaz.com

Please specify the connection string for the database to use.

By default, a local SQLite database is created in the environment

directory. It is also possible to use an already existing

PostgreSQL database (check the Trac documentation for the exact

connection string syntax).

Database connection string [sqlite:db/trac.db]> <Enter>

Please specify the type of version control system,

By default, it will be svn.

If you don’t want to use Trac with version control integration,

choose the default here and don’t specify a repository directory.

in the next question.

Repository type [svn]> <Enter>

Please specify the absolute path to the version control

repository, or leave it blank to use Trac without a repository.

You can also set the repository location later.

Path to repository [/path/to/repos]> /var/www/svn/svnrepos/site-sohailriaz.com

Please enter location of Trac page templates.

Default is the location of the site-wide templates installed with Trac.

Templates directory [/usr/share/trac/templates]> <Enter>

…………………..

…………………..

…………………..

Congratulation!

Edit /etc/httpd/conf.d/trac.conf and change /var/trac to /var/www/trac at line starting from PythonOption TracEnvParentDir

vi /etc/httpd/conf.d/trac.conf

following line should be like this

PythonOption TracEnvParentDir /var/www/trac

Create user account for trac access

htpasswd -cb /var/www/trac/.htpasswd tracuser1 passw0rd

Change ownership and group member to apache of trac instances.

chown -R apache:apache /var/www/trac/site-sohailriaz.com

Restart webserver to take changes.

/etc/init.d/httpd restart

Now browse the site and you will see all available projects under trac and then open the project to browse by viewing source.

REFERENCES

http://www.sohailriaz.com/how-to-install-subversion-with-trac-on-centos-5-x/