1. Chapter 6: Linux Filesystem Administration

2. The /dev directory Each device is represented as files in /dev
Devices are divided into two types
Character
Block
The first character in the long listing indicates the type of the device
Major and minor numbers replace the size. Major for the type of the device and minor for the device itself
If a device file is corrupted or deleted you can use mknod to re-create it if you know the type, major and minor numbers. $mknod /dev/fd10 b 2 10
Otherwise, you can use: $/dev/MAKEDEV fd0
The file /proc/devices contains a list of used devices

3. Common Device Files

4. File Systems
An advantage of Linux is that you can use several files systems at the same time, thus:
Each partition can have its own file system
Mounting means making the data available
A storage device can be mounted to any directory in the system
It is common to use directories under /mnt
Mounting will temporary covers up all the content of the mount point for the duration of mounting
To mount and un-mount devices, use the mount/ unmount commands
The file system table (/etc/fstab) contains various information about currently mounted devices

5. Common File Systems

6. Floppy Disks
To format a floppy disk (i.e. creating a file system) you use the mkfs commands
mkfs takes a –t option to specify the file system type and you need to specify the device file to be used
$ mkfs –t ext3 fd4
The default file system is ext2
A list of variant to mkfs is given in Table 6-3
A disk should be mounted to be accessible
The command mount lists currently mounted file systems
Similar effect can be achieved by viewing the mount table. $cat /etc/mtab
After mounting, use the mount point as the root dir.

7. Floppy Disks (cont.)
When an ext2 is created on a device, a directory called lost+found is created by default
To check if a mounted directory is not used by any users, you use the fuser: $fuser –u /mnt/floppy
You need to unmount the floppy disk before ejecting it. To do so, use $unmount /mnt/floppy
The unmount commands accepts the device to be un-mounted or the mount point directory
You can use the fuser to check if any process is using the mount directory which will prevent the device from being un-mounted
The file-systems table is used to mount devices at boot time and in case the mount command does not have enough arguments

8. Floppy Disks (cont.)
The /etc/fstab has six fields: Device to mount, mount point, type, mount options, dump#, fsck#
The dump# determines if the FS is to be backed up or not
The fsck# determines if FS is to be checked at boot or not
The mount can take fewer arguments
Example: $mount /dev/fd0 or $mount /mnt/floppy
Contents of /etc/fstab
Generally, floppy disks are mounted automatically when using a GUI environment such as the KDE or the GNOME

9. CD-ROMs
They are different than floppies in which they usually use IDE controller
Thus, they use similar naming convention like IDE hard disks (hda for primary master, etc.)
Besides, they typically use the iso9660 filesystem, thus they are mounted with
-t iso9660 option for the filesystem type
-r for read-only
$mount –r –t iso9660 /dev/cdrom /mnt/cdrom
They can be un-mounted using unmount
CD-ROM can NOT be ejected unless properly un-mounted.

10. Hard Disks They are usually partitioned with different FS why
Separate different data types
Use of more than FS
Improve system reliability (FS corruption)
Enhance system performance
The MBR stores info about all partitions
Hard disk structure: Tracks, sectors, cylinder
Physical and logical partitions
Partitioning hard disks:
During installation: using Druid
After installation: Using fdisk
The machine might need to be rebooted to manually reload the new partition info

11. Maintenance Commands Monitoring disk usage using disk free space (df)
It gives results in terms of block numbers
The –h option prints results measured in MB & GB
It only views mounted file systems
To get info about a specific directory use du (Directory Usage)
It, du, gives results in KB
The option –s give summary and can be used with –h
To view total number of i-nodes and the number of free ones use: dumpe2fs –h /dev/sda0

12. Maintenance Commands (cont)
Disk quotas
Soft limit and hard limit
Setting quotas (quotaon/quotaoff)
Editing quota (edquota)
List quota values for all users (repquota)
Checking quota values for individual users (quota –v <user>)