Chapter 6: Linux Filesystem Administration

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

Common Device Files

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

Common File Systems

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.

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

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

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.

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

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

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>)