Chapter 5: Linux Filesystem Administration

Hard limit

limit cannot be exceeded

fuser -u command

lists users using a directory

repquota command

report user quotas

quotaon and quotaoff commands

toggle quotas on and off

Bad blocks

unusable areas of a disk (cannot hold a magnetic charge)

vgextend command

used to add a new PV to an existing VG

mkisofs command

used to create ISO image from a directory of files takes at least 2 arguments: - filename to be created - directory used to create the ISO image

lvcreate command

used to create LVs from available space in VG

vgcreate command

used to create a VG that uses the space in PVs arguments are name of the VG and PVs to be used

pvdisplay command

used to display detailed information about each PV

vgdisplay command

used to display detailed information about each vg

lvdisplay command

used to display information about each LV

lvextend

used to increase the size of an LV i.e., to use space extended onto an existing VG

/etc/fstab file

used to mount devices at boot time also consulted when users do not specify enough mount command arguments 6 fields: - device to mount - mount point - type - mount options - dump# - fsck#

mount command

used to mount devices to mount point directories when used with no options or arguments, lists currently mounted filesystems

mknod command

used to re-create a corrupted device file Must know file type, major, and minor numbers

umount command

used to unmount devices from mount point directories

Hard disk quotas

user limits on filesystem usage Quotas can restrict number of files/directories or total disk space usage

Root filesystem

when the Linux system is first turned on, a filesystem on the hard drive is mounted to the / directory (contains most OS files)

/run/media/username directory

In GUI environment, CD or DVD automatically mounted to a directory underneath the /run/media/username directory Named for the label on the CD or DVD System places shortcut within the GUI environment

cfdisk command

Interactive graphical utility for creating, manipulating and deleting partitions Reboot computer after using the command to ensure proper reloading into memory

Master Boot Record (MBR) or Master Boot Block (MBB)

Partition definitions stored in the first readable sector of the hard disk

Partition

Physical division of an HDD; can have its own filesystem

mkswap command

Prepare the swap partition

Syncing

Process of writing data stored in RAM to the HDD

yum install quota command

Quota support is not installed on Fedora 20 by default

iso9660 filesystem

Typically used by CDs and DVDs and are read-only when accessed using Linux mount with -r (read only) option cannot be ejected until properly unmounted can be used to create ISO images that contain other files can be mounted as a loopback device using the mount command

Physical Volumes

Unused partitions on hard disks that the LVM can use to store information

Logical Volumes (LVs)

Usable volumes that are created by the LVM from the available storage space within a VG You work with mount points of LVs as you would work with any other had disk partition device file Edit /etc/fstab to ensure that LVs are automatically mounted at system startup

tune2fs command

Used to change filesystem parameters -i option sets interval to forcing full system check

parted (GNU Parted) command

Used to create and modify partitions on both MBR and GPT hard disks

pvcreate command

Used to create physical volumes (PV)

Logical Volume Manager (LVM)

Used to create volumes

mkfs (make filesystem) command

Used to format a disk device with a filesystem -t option specifies filesystem type default is ext2

Soft limit

User may exceed quota briefly For a certain period of time (seven days by default)

Disk usage

Using more filesystems typically results in less hard disk space per filesystem May result in errors when filesystems fill up with data Periodically remove obsolete files such as old log files to make room for new ones

du (directory usage) command

View size of a directory and contents in kilobytes -s option: summarizes output - h option more user friendly format

dumpe2fs command

View total number of inodes and free inodes for an ext2, ext3, or ext4 filesystem - h option: more user friendly format

GUID Partition Table (GPT)

You can't use the fdisk or cfdisk commands to create and modify partitions before you format them with a filesystem or prepare them for use as swap memory

Major number

a number in a device file that points to the device's driver in the Linux kernel Several different devices can share the same major number if they are of the same general type

quota command

allows regular users to view their own quotas and current usage

Swap partitions

do not contain a filesystem, you must still prepare and activate them for Linux

edquota command

edit user quotas

Filesystem corruption

errors in filesystem structure preventing retrieval of data Commonly occurs due to improper system shutdown

Filesystems

formatting: creating a filesystem on a device All storage media need to contain a filesystem before they can be used

Minor number

indicates the particular device

GPT partitions support filesystem commands

- Format partitions with a filesystem using mkfs command - Mount them to the directory tree with the mount command - Update the /etc/fstab file to mount them automatically

Device File

A file representing a system device One file per device, typically found in the /dev directory Specifies how to transfer data to and from the device

3 types of hard disks:

- PATA - SATA - SCSI SATA & SCSU are well-suited to Linux servers - Faster access speed - Multiple hard drives can be attached to a controller

LVM components

- Physical Volumes (PVs) - Volume Groups (VGs) - Logical volumes (LVs)

PATA HDD

- Primary Master /dev/hda - Primary Slave /dev/hdb - Secondary Master /dev/hdc - Secondary Slave /dev/hdd different device file for each

For PATA drives

- Primary master /dev/hda - Primary slave /dev/hdb - Secondary master /dev/hdc - Secondary slave /dev/hdd

swapon command

Activate the swap partition Edit /etc/fstab file to ensure that new swap partition is activated as virtual memory

Physical Extent (PE) size

Block size for saving data in a VG - Should be set when creating a VG - Can use vgcreate -s to set the PE

Working with CDs, DVDs and ISO images

Can be mounted with mount command and unmounted with umount Different device file, depends on the technology used by the drive itself

Volumes

Can contain filesystems and can be mounted to directories More flexible than standard partitions, allows use of free space across multiple hard disks Has error correction abilities

e2fsck command

Check an ext2, ext3, or ext4 filesystem -c option checks for bad blocks

Monitoring Filesystems

Check mounted filesystems periodically for: - Errors - Disk space usage - Inode usage Minimizes problems that can occur as a result of a damaged filesystem Reduces the likelihood that a file cannot be saved due to insufficient disk space

Unique characteristics of a device file

Consists of the device file type (block or character), major number, and minor number

Volume Groups

Contain one or more physical volumes (PVs)

gdisk command

Create and work with partitions on GPT hard disk

swapoff command

Deactivate the swap partition

Mount point

Directory to which a device is attached the mounted device temporarily covers up the contents of the mount point Any existing directory can be a mount point Create empty directories used specifically for mounting devices to prevent making files inaccessible

pvscan, vgscan, lvscan commands

Display information about PVs, VGs, and LVs, respectively

Mounting new filesystems automatically at boot time

Edit /etc/fstab file to allow system to mount new filesystems automatically at boot time

SCSI

First SCSI HDD (/dev/sda) Second SCSI HDD (/dev/sdb) Third SCSI HDD (/dev/sdc)

Advantages of multiple partitions

It is good practice to use more than two partitions - segregate different types of data - Allow for use of multiple filesystem types on one HDD - Reduce chance that filesystem corruption will render a system unusable - Speed up access to stored data

For SATA or SCSI drives

Linux may use many or different names, depending on the actual CD or DVD drive To make identification of CD/DVD driver easier, Fedora Linux creates a file called /dev/cdrom (a symbolic link to the correct device file for your first CD or DVD drive)

Minimum required partitions

Linux requires at least 2 partitions: - root - swap

df (disk free space) command

Monitor free space used by mounted filesystems -h option: to view a more user friendly format To get information about different filesystems, you must mount them prior to using df command

SSD

Most SSDs are SATA and are treated like a SATA hard disk by Linux /dev/sda could refer to the first SATA hard disk or the first SATA SSD

Removable Storage

Most removable storage devices emulate SCSI protocol int he firmware of the device Devices are automatically mounted to a new directory under the /media directory named for the label on the device Easy to work with removable storage devices using a GUI interface If you want to use commands, you must know the device file and mount point directory

Block devices

Transfer chunks or blocks of data using physical memory to buffer the transfer Faster data transfer than character devices i.e., Floppy disks, CD-ROMS, DVDs, USB flash drives, hard disk drives

Character devices

Transfer data character-by-character to and from the device

View list of devices that are currently used on the system and their major numbers

cat /proc/devices

fsck command

check a filesystem for errors Filesystem must be unmounted -f option used to perform full check -a or -y automatically repair any errors

fdisk command

create partitions after installation - Specify hard disk partition as an argument - Variety of options for fdisk prompt to achieve different tasks Reboot computer after using the command to ensure proper reloading into memory

Mounting

making a device accessible to users via the logical directory tree