Disks, Filesystems, and Mounting

Question 1

Linux allows low level access to…?

Answer 1

disk drives through device nodes in the /dev directory.

Question 2

Usually, disks are _______ with a filesystem, and _______ to a directory instead.

Answer 2

formatted, mounted.

Question 3

Filesystems are created with some variant of the…?

Answer 3

mkfs command.

Question 4

The default filesystem of Red Hat Enterprise Linux is the..?

Answer 4

ext3 filesystem.

Question 5

The mount command is used to map the root directory of a disk’s (or a disk partition’s) filesystem to an…?

Answer 5

already existing directory. (This directory is then referred to as a mount point.

Question 6

The umount command is used to …?

Answer 6

unmount a filesystem from a mount point.

Question 7

The df command is used to report…?

Answer 7

filesystem usage, and tables currently mounted devices.

Question 8

Linux Disk Device Nodes:

/dev/fd0 disk type…?

Answer 8

floppy disk

Question 9

Linux Disk Device Node:

/dev/hda disk type…?

Answer 9

IDE Primary Master

Question 10

Linux Disk Device Node:

/dev/hdb disk type…?

Answer 10

IDE Primary Slave

Question 11

Linux Disk Device Node:

/dev/hdc disk type…?

Answer 11

IDE Secondary Master

Question 12

Linux Disk Device Node:

/dev/hdd disk type…?

Answer 12

IDE Secondary Slave.

Question 13

Linux Disk Device Node:

/dev/sd[a-z] …?

Answer 13

SCSI Disks

Question 14

Linux Disk Device Node:

/dev/cdrom …?

Answer 14

Symbolic Link to CD/ROM

Question 15

Although device nodes exist for disk drives, usually standard users do not have…?

Answer 15

permissions to access them directly.

Question 16

More often than not, hard disks are further divided into partitions. Partitions are regions of the hard disk that can…?

Answer 16

each be used as if it were a separate disk.

(Just as there are device nodes for every disk, there are also device nodes for every disk partition. The name of a partition’s device node is simply the partition number appended to the name of the disk’s device node. For example, the device node for the third partition of the primary slave IDE drive is called /dev/hdb3.)

Question 17

By accessing disk drives through their device nodes, users may see (and write) the contents of the drive byte for byte. To the user, the drive looks like a (very big) file. When elvis cats the contents of a file to the drive’s device node, the information is…?

Answer 17

Transferred, byte for byte, to the drive.

Question 18

On the floppy, what is the filename associated with the information?

Answer 18

Trick question. It doesn’t have one. Who is the user owner? What are the permissions? There are none. It’s just data.

Question 19

A filesystem provides order to disk drives by organizing the drive into…?

Answer 19

Fixed sized chunks called blocks.

(The filesystem then organizes these blocks, effectively saying “this block is going to contain only inodes”, “this block is going to contain only dentries”, “these 3 block over here, and that one over there, are going to contain the contents of the file /etc/services”, or “this first block is going to store information which keeps track of what all the other blocks are being used for”. Filesystems provide all of this structure that is usually taken for granted.)

Question 20

Before a disk can be used to store files in a conventional sense, it must be…?

Answer 20

initialized with this type of low level structure. In Linux, this is usually referred to as “creating a filesystem”. In other operating systems, it is usually referred to as “formatting the disk”.

Question 21

Linux supports a large number of different types of filesystems (the fs(5) man page lists just a few). While Linux’s native filesystem is the ext2 (or in Red Hat Enterprise Linux, the ext3) filesystem, it also….?

Answer 21

supports the native filesystems of many other operating systems, such as the DOS FAT filesystem, or the OS/2 High Performance File System.

Question 22

In Linux, filesystems are created with some variant of the mkfs command. Because these commands are usually used only by the administrative user, they do not…?

Answer 22

live in the stadard /bin or /usr/bin directories, and therefore cannot be invoked as simple commands. Instead, they live in the /sbin directory, which is reserved for administrative commands.

Question 23

The mkfs command, and its variants, can be configured with a large collection of command line switches which specify…?

Answer 23

low level details about the filesystem. These details are beyond the scope of this course, however. Fortunately, the various options default to very reasonable general purpose defaults. For the curious, more information can be found in the mkfs.ext2(8) and similar man pages.

Question 24

Once a disk or a disk partition has been formatted with a filesystem, users need some way to access the directories and files that the filesystem provides. In other operating systems, sers are usually very aware of disk partitions, because they have to refer to them using labels such as C: or D:. In Unix, users are…?

Answer 24

often unaware of partitions, because different disk partitions are organized into a single directory structure.

Question 25

Every filesystem provides a root directory that serves as…?

Answer 25

the base of that filesystem.

Question 26

Upon booting the system, one of your disk’s partitions acts as the…?

Answer 26

root partition, nd its root directory becomes the system’s root directory /.

Question 27

The / directory has subdirectories, and those subdirectories have subdirectories, all of which reside in …?

Answer 27

the root partition’s filesystem.

Question 28

If a system has multiple disks, however, or if a disk has multiple partitions, the story gets…?

Answer 28

more complicated.

Question 29

In order to access the filesystems on the other partitions, the root directories of those filesystems are…?

Answer 29

mapped to an already existing directory through a standard Unix technique called mounting.

Question 30

How can a user determine which directories are being used as mount points?

Answer 30

One approach is to run the mount command without arguments.

Question 31

Without arguments, the mount command returns a list of …?

Answer 31

current mount points, the device that is mounted to it, the type of filesystem that device has been formatted with, and any mount options associated with the mount.

Question 32

virtual filesystems…?

Answer 32

are implemented by the kernel directly, and do not exist on any physical device.

Question 33

If you seldom know which directories are being used as mount points, and which files exist in which partitions, why bother even talking about it?

Answer 33

or now, we will address two reasons. The first reason is that there can be subtle issues that creep up which are related to the underlying filesystem. Partitions can run out of space. If a filesystem mounted on /home runs out of space, no more files can be created underneath the /home directory. This has no effect on the /tmp directory, however, because it belongs to another filesystem. In Unix, when a partition fills up, it only effects the part of the directory structure underneath its mount point, not the entire directory tree.

Question 34

Users can determine how much space is available on a partition with the…?

Answer 34

df command, which stands for “disk free”.

Question 35

df [OPTION…] [FILE…] …?

Answer 35

Show information about all partitions, or partition on which FILE resides.

Question 36

df command switch:

-a, –all…?

Answer 36

Shows all filesystems, including those of size 0.

Question 37

df command switch:

-h, –human-readable …?

Answer 37

Print sizes in human readable format.

Question 38

df command switch:

-i, –inodes …?

Answer 38

List inode usage instead of block usage.

Question 39

df command switch:

-T, –print-type …?

Answer 39

Include filesystem type.

Question 40

Not only will the df command show how much space is left on particular partitions, but it also gives a very readable table of which…?

Answer 40

devices are mounted to which directories.

Question 41

The second reason users need to be aware of filesystems and mount points involves…?

Answer 41

temporary media such as floppies and CD/ROM drives. Like any block device, floppy disks and CD/ROM disks are formatted with filesystems. In order to access these filesystems, they must be mounted into the directory structure, using a (already existing) directory as a mount point.

Question 42

By default, only the root user can…?

Answer 42

mount and unmount devices.

Question 43

The “Console User” (someone who has logged in from a virtual console or the X login screen) gains ownership of devices associated with…?

Answer 43

the physical machine, such as a floppy drive, and special permissions to mount these devices to predefined mount points, such as /media/floppy. If a user has logged in by some other technique, such as over the network, or via the su command, they will not be considered the “Console User”, and will not have permissions to mount these devices.

Question 44

A filesystem can only be unmounted if it is considered…?

Answer 44

“non-busy”.

Question 45

What can keep a filesystem “busy”?

Answer 45

Any open file, or any process that has a current working directory in the filesystem, “busy”s the filesystem. The only way for the filesystem to be unmounted is to track down any processes that might be keeping the filesystem “busy”, and kill them.

Question 46

The GNOME graphical environment runs an automounter, which keeps an eye on the…?

Answer 46

CD/ROM drive, and will automatically mount the filesystem of any newly inserted disk.

Question 47

The automounter is part of the graphical environment, and does not…?

Answer 47

exist if a user logged in through a virtual console.

Question 48

he automounter only works for the…?

Answer 48

CD/ROM drive. The floppy drive, or other devices, must be mounted “manually”.

Question 49

In order to improve performance, the kernel buffers all…?

Answer 49

block device (harddrive) interactions. For example, when you copy a file to a floppy, the file might seem to have been copied almost immediately. Later, when you unmount the floppy with the umount command, the command takes a while to return while writes are being committed to the floppy. When unmounting the device, the kernel is forced to commit all pending transactions to the disk.

Question 50

What would happen if you removed the floppy from the drive before buffered writes were committed to disk?

Answer 50

At best, the files that you thought you had copied to the floppy would not be there. At worst, you may have a corrupted floppy, and a confused Linux kernel the next time someone tries to mount a floppy.