LPI Linux Certification in a Nutshell (40 page)

• IDE disks are known as
  /dev/hda
  ,
  /dev/hdb
  ,
  /dev/hdc
  ,
  /dev/hdd
  , and
  so on.
  

• Any disks using the SCSI emulation layer are known as
  /dev/sda
  ,
  /dev/sdb
  ,
  /dev/sdc
  , and so on. These include SCSI
  disks, SATA disks, and, in newer kernels, IDE disks.
  

• Three types of partitions:
  

  Primary
  

  Filesystem container. At least one must exist, and up
  to four can exist on a single physical disk. They are
  identified with numbers 1 to 4, such as
  /dev/hda1
  ,
  /dev/hda2
  , and so on.
  

  Extended
  

  A variant of a primary partition, but it
  cannot contain a filesystem. Instead, it contains one or
  more
  logical partitions
  . Only one
  extended partition may exist, and it takes one of the four
  possible spots for primary partitions.
  

  Logical
  

  Created
  within
  the
  extended partition. From 1 to 12 logical partitions may be
  created. They are numbered from 5 to 16, such as
  /dev/hda5
  ,
  /dev/hda6
  , and so on.
  

• Up to 15 partitions with filesystems may exist on a single
  physical disk.
  

• The Linux kernel supports many different kinds of
  filesystems:
  

  ext3
  

  The third extended filesystem. A journaling
  filesystem, this has been the default for most Linux
  distributions since the early 2000s.
  

  ext2
  

  The second extended filesystem. This was the initial
  default Linux filesystem.
  ext3
  is
  basically
  ext2
  with journaling
  support.
  

  xfs
  

  Journaling filesystem created by Silicon Graphics for
  IRIX and ported to Linux.
  

  reiserfs
  

  This was the first journaling filesystem introduced in
  the standard Linux kernel.
  

  vfat
  

  A Microsoft Windows filesystem for Windows 95, 98, and
  ME systems.
  

• The top of the filesystem tree is occupied by the
  root filesystem
  . Other filesystems are
  mounted under it, creating a unified filesystem.
  

• /etc
  ,
  /lib
  ,
  /bin
  ,
  /sbin
  , and
  /dev
  must be part of the root
  filesystem.
  

fdisk
[
device]


Manipulate or display the partition table for
device
using a command-driven
interactive text interface.
device
is
a physical disk such as
/dev/hda
, not a
partition such as
/dev/hda1
.

mkfs
device


Make a filesystem on
device
,
which must be a partition.

mkswap
device


Prepare a partition for use as swap space.

df
[
directories
]

Display overall disk utilization information for
mounted filesystems on
directories
.

du
[
directories
]

Display disk utilization information for
directories
.

fsck
filesystems


Check
filesystems
for errors
and optionally correct them.

dumpe2fs
filesystem


Display the detailed information about the
ext2
or
ext3
filesystem at
filesystem
.

tune2fs
filesystem


Modify filesystem variables for the
ext2
or
ext3
filesystem at
filesystem
.

• /etc/fstab
  contains mount
  information for filesystems. Each line contains a single
  filesystem entry made up of six fields, shown in
  Table 10-11
  .
  

• The
  /media
  directory is often used by
  distributions as a place to automount hotplug devices, such as USB
  drives.
  

  Table 10-11. Fields found in the /etc/fstab file
  

  Entry	Description
  Device	The device file for the partition holding the filesystem.
  Mount point	The directory upon which the filesystem is to be mounted.
  Filesystem type	A filesystem type, such as ext3 .
  Mount options	A comma-separated list.
  Dump frequency	For use with dump .
  Pass number for fsck	Used at boot time.

mount
device


mount
directory


mount
device
directory


Mount filesystems onto the hierarchy. The first and second
forms consult
/etc/fstab
for additional
information.

umount
device


umount
directory


Unmount the filesystem on
device
or mount it on
directory
.

ext2

The standard Linux filesystem.

ext3

A journaling filesystem that is backward-compatible with
ext2
.

iso9660

The standard CD-ROM format.

vfat

The Microsoft Windows FAT filesystem.

nfs

Remote servers.

proc

A system abstraction for access to kernel
parameters.

swap

Swap partitions.

Per-user hard

The maximum size for an individual.

Per-user soft

A warning threshold.

Per-group hard

The maximum size for a group.

Per-group soft

A warning threshold.

Grace period

A time restriction on the soft limit.

quota
user


quota -g
group


Display quota limits on
user
or
group
.

quotaon
[
filesystems
]

Enable previously configured disk quotas on one or more
filesystems
.

quotaoff
[
filesystems
]

Disable disk quotas on one or more
filesystems
.

quotacheck
[
filesystems
]

Examine filesystems and compile quota databases. Usually
run via
cron
.

edquota
names


Modify user or group quotas by spawning a text
editor.

repquota
filesystems


Display a summary report of quota status for
filesystems
, or use
-a
for all
file
systems.

Enabling quotas requires
usrquota
and/or
grpquota
options in
/etc/fstab
, creation of
quota.user
and
quota.group
files at the top of the filesystem, a
quotacheck
, and a
quotaon
.

• Access control is implemented using a set of
  properties called the
  access mode
  , stored in
  the inode. Three classes of user are defined:
  

  User
  

  The user who owns the file.
  

  Group
  

  The group that owns the file.
  

  Other
  

  All other users on the system.
  

• Three permissions are either granted or not granted to each
  class of user:
  

  Read (
  r
)
  

  Allows access to file contents and listing of
  directory contents.
  

  Write (
  w
)
  

  Allows writing a file or creating files in a
  directory.
  

  Execute (
  x
)
  

  Allows execution of a file and ability to read/write
  files in a directory.
  

• These comprise nine bits in the mode User
  rwx
, Group
  rwx
, and Other
  rwx
.
  

• Three additional mode bits are defined:
  

  SUID
  

  To grant processes the rights of an executable file’s
  owner.
  

  SGID
  

  To grant processes the rights of an executable file’s
  group.
  

  Sticky bit
  

  Prohibits file deletion by nonowners.
  

• These 12-mode bits are often referred to in octal notation
  as well as with mnemonic constructs.
  

• Mode bits are displayed using such commands as
  ls
  and
  stat
  .
  

• New files receive initial access mode as described by the
  umask
  .
  

• The
  umask
  strips specified bits from
  the initial mode settings. Typical umasks are 002 and 022.
  

• Existing file modes are changed using
  chmod
  with either symbolic or octal mode
  specifications:
  

  • Symbolic:
    

    [ugoa][-+=][rwxXst]
    

  • Octal bits:
    

    user r, w, x, group r, w, x, other r, w, x
    rwxrwxrwx = 111111111 = 777
    rwxr-xr-- = 111101100 = 751
    

chmod
mode
files


Modify the access mode on
files
using a symbolic or octal
mode
.

chown
user-owner
.
group-owner
files


Change the owner and/or group of
files
to
user-owner
and/or
group-owner
.

chgrp
group-owner
files


Change the group ownership of
files
to
group-owner
.

chgrp
functionality is included in
chown
.