laksh mi. fdisk is an interactive utility to manipulate disk partitions. use fdisk –l to review...
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Linux File System PRESENTED BY
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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: [email protected]
WEBSITE:WWW.QUONTRASOLUTIONS.COM
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