Linux File System PRESENTED BY

QUONTRA SOLUTIONS IT TRAINING AND PLACEMENT SUPPORT

CONTACT: 404-900-9988 EMAIL: info@quontrasolutions.com

WEBSITE:WWW.QUONTRASOLUTIONS.COM

lakshmi

Partitions & the fdisk command

fdisk is an interactive utility to manipulate disk partitions.

Use fdisk –l to review the disks and partitions on the system.

Use fdisk and the disk special device file in order to create new partitions.Example:# fdisk /dev/hda

Partitions & the fdisk command

The fdisk command supports many types of partitions.

Alternative: Gnu parted – create, copy and

manipulate partitions. Sfdisk

Supported Local File Systems

Linux Supports vast amount of local, disk based, file systems. For example: Ext 2 – previous native Linux file system. Ext 3 – Current native Linux file system. Vfat – DOS 32 file system.

ISO9660 – CDROM Image file system.

Ext 3 File System

Ext 3 is the default FS in many Linux distributions.

Ext 3 is a journal FS, thus improves data integrity and system availability (fast fsck).

Ext 3 is an improvement of Ext 2, so transfer to Ext 3 is considerably easy.

Ext 3 FS is part of Linux Kernel since version 2.4.16.

Super

Block

Ext 3 File System Structure

GroupDisctipto

rs

BlockBitma

p

InodeBitma

p

InodeTable Data Data Data

Block Group

Same for all block groups

Ext 3 File System Structure

Ext 3 FS is divided to block groups in order to reduce seek time and preserve data integrity (reduce fragments).

Each block group contains the following: Super Block – the super block contains

data about the status of the current FS.There are several instances of the Super Block on the FS. Each instance is stored at an offset of 1024 Bytes from the previous one.

Ext 3 File System

StructureThe Super Block contains the following

data: Number of Inodes on the FS and the number of

free Inodes. Number of data blocks on the FS and the number

of free data blocks.

Time and mounting point of the last system mount.

Flags indicating the state of the FS. Number of times the FS was mounted. Time the FS was last checked. Maximum time permissible between checks. Magic number indicating an Ext 3 FS.

Ext 3 File System Structure

Group Discriptors – Contain information about the block group. Such as:

The address of the block containing the block bitmap of the group.

The address of the block containing the inode bitmap of the group.

The address of the block containing the indoe table of the group.

Ext 3 File System Structure Block bitmap indicates which blocks in the

group have been allocated. Inode bitmap indicates which Inodes in

the group have been allocated. Inode table is an array of Inodes for that

particular group.

Creating Ext 3 File System Use mkfs command to create Ext 3 FS. Example:# mkfs -t ext3 -b 2048 -j -L local /dev/hdb1

-t - FS type (default Ext 2) -b - Block Size (Default 1024) -j - Journaled -L - volume label

The dumpe2fs Command

Use the dumpe2fs command in order to view the properties of the Ext2/Ext3 file system.

The dumpe2fs command prints the super block and blocks group information for the file system present on device.

Converting Ext 2 to Ext 3

Use tune2fs to convert exsisting Ext 2 FS to Ext 3 FS.

Example:# tune2fs -j -L local /dev/hdb1

-j - Add journal to the FS -L - Volume Label

Using the fsck Command

File system status must be clean in order

to be mounted and made available on

the system.

The fsck command is used to check the

consistancy of the file system, and

optionally, repair it.

Using the fsck Command

Usage:fsck [-fp] [-b superblock ] device

-f – Force FS check. When the superblock indicates the FS state is clean, fsck exits automatically. Use this option to force fsck check.

-p – Fix file system inconsistancies automatically (rather then interactivly asking for intervention).

Device – Logical device name or volume label.

Using the fsck Command

# fsck -f /dev/hda1fsck 1.32 (09-Nov-2002)e2fsck 1.32 (09-Nov-2002)Pass 1: Checking inodes, blocks, and sizesPass 2: Checking directory structurePass 3: Checking directory connectivityPass 4: Checking reference countsPass 5: Checking group summary information/boot: 35/26520 files (2.9% non-contiguous), 12575/105808 blocks

Restoring Damaged Superblock

Use fsck with -b superblock option to restore damaged superblocks from backup.

If the superblock of the FS is damaged, there could be no access to data on the FS.

Ext 3 keeps backups of the Superblock. Use mkfs with the -n option to find out

the location of the superblock backup.

# mkfs -t ext3 -n /dev/hda1

mke2fs 1.32 (09-Nov-2002)

Filesystem label=

...

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729

Superblock Back up Locations

Restoring Damaged Superblock

Restoring DamageSuperblock

# fsck -b 8193 /dev/hda1fsck 1.32 (09-Nov-2002)e2fsck 1.32 (09-Nov-2002)/boot was not cleanly unmounted, check forced.Pass 1: Checking inodes, blocks, and sizes...Pass 5: Checking group summary information /boot: ***** FILE SYSTEM WAS MODIFIED *****/boot: 35/26520 files (2.9% non-contiguous), 12575/105808 blocks

• Use the information gained by the mkfs command to salvage the FS superblock:

Mounting File Systems

In order to make the file system available for use, the file system must be mounted.

Use a directory as a mount point, to connect the file system about to be mounted to the file system tree, starting from root (/).

Each directory can be used to mount one file system at a time.

A directory that is being used can not serve as a mount point.

Mouting File Systems

/

usr

home

etc

local

hda1

bin

sbin

lib

hdb1

bin

sbin

The Mount Command

Use the mount command in order to make FS available.

Syntax:mount -t type -o options

logical_device mount_point Example:

# mount -t ext3 -o noatime

/dev/hdb1 /usr/local

The Mount Command

-t – file system type. Local file systems could be: Ext 2 (default)

Ext 3

msdos – FAT 16 FS

vfat – FAT 32 FS

ntfs - Windows NT

The Mount Command

-o – Mount option. Options could be: ro – read only. rw – read and write. suid/nosuid – allow/deny suid bit to take

effect. exec/noexec – permit/deny the execution

of binaries. noatime – do not update file access time

(makes FS much faster).

The Mount Command

logical_device – this could be either a

logical device name like: dev/hdb1

or, a volume label like: LABEL=local

mount_point – A directory that would

serve as the mount point for the file

system.

The /etc/fstab File

The /etc/fstab file is used to mount FS

automatically at boot time or to make

the mounting of frequently mounted FS

easier.

The /etc/fstab is created during

system installation and should be edited

manually to include filesystems needed

to be available when system starts.

The /etc/fstab File

LABEL=/ / ext3 defaults 1 1

LABEL=/boot /boot ext3 defaults 1 2

none /dev/pts devpts gid=5,mode=620 0 0

none /proc proc defaults 0 0/dev/hda3 swap swap defaults 0 0

/etc/fstab file structure

The /etc/fstab File

Device to Mount – Logical device name

or Volume Label of the device to be

mounted.

Mount Point – The directory to be the

mount point of the file system.

File System Type – The type of te file

system to be mounted.

The /etc/fstab File

Mount Options – options should be used while working with the file system (defaults = rw, suid, exec, auto, nouser, async).

FS Backup – is used by the dump tool to decide which FS needs to be backed up. Accepted values are 0 for no backup, or 1 indicating this file system needs to be backed up.

The /etc/fstab FileFS Check Pass – the order by which file

systems needs to be checked before being

mounted. Acceptable values are 1 to 9. File systems are being checked according

to the order starting with 1 ending with 9. File systems with FS check pass 1 are

being checked one after the other, while file systems with FS check pass 2 and up are being checked in parallel.

The /etc/fstab File

fsck will try and correct any error it encountered which does not require changes to the file system.

If the error requires changes to the file system, the system drops to single user mode and fsck must be run manually.

The /etc/fstab File and mount Upon writing an incomplete mount

command, mount will try and get the missing information from /etc/fstab

Use the mount -a command to mount all local file

systems listed in /etc/fstab (excpet those

indicating noauto in the mount options).

/etc/mtab File

The /etc/mtab file contains information about all mounted file systems.

The /etc/mtab file is dynamically changed by the system and should not be edited manually.

/etc/mtab File

# cat /etc/mtab

/dev/hda2 / ext3 rw 0 0

none /proc proc rw 0 0

none /dev/pts devpts rw,gid=5,mode=620 0 0

usbdevfs /proc/bus/usb usbdevfs rw 0 0

/dev/hda1 /boot ext3 rw 0 0

none /dev/shm tmpfs rw 0 0

Example of/etc/mtab file:

The umount Command

Use the umount command to make file systems unavailable.

Command usage: umount dir | device Use either mount point or logical device name to

make a file system unavailable.

The umount Command

File systems could not be made unavailable if resources on that file system is being used.# cd /boot

# umount /boot

umount: /boot: device is busy

• Use fuser -v -m logical_device to check

which processes are using the file system.

The umount Command

Example:

#fuser -v -m /dev/hda1

USER PID ACCESS COMMAND

/dev/hda1 root 2471 f.... vi

The umount Command

# fuser -k -m /dev/hda1

/dev/hda1: 2471

• Use fuser -k -m device to kill processes

making use of the file system.

Linux File System PRESENTED BY

QUONTRA SOLUTIONS IT TRAINING AND PLACEMENT SUPPORT

CONTACT: 404-900-9988 EMAIL: info@quontrasolutions.com

WEBSITE:WWW.QUONTRASOLUTIONS.COM

THANK YOU