10.2 Devices, Linux Filesystems,
and the Filesystem Hierarchy Standard (Topic 2.4)
10.2.1 Objective 1: Create
Partitions and Filesystems
10.2.1.1 Disk drives and
partitions
-
IDE disks are
known as /dev/hda, /dev/hdb, /dev/hdc,
and /dev/hdd.
-
SCSI disks are
known as /dev/sda, /dev/sdb, /dev/sdc,
and so on.
-
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/hda10, and so on.
10.2.1.2 The root filesystem and
mount points
-
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.
10.2.1.3 Partition and filesystem
management commands
The following commands are commonly used to
repair and manage filesystems:
- 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.
- mkswap
device
-
Prepare a partition for use as swap
space.
10.2.2 Objective 2: Maintain the
Integrity of Filesystems
These commands are
commonly used in day-to-day filesystem maintenance:
- 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.
10.2.3 Objective 3: Control
Filesystem Mounting and Unmounting
10.2.3.1 Managing the filesystem
table
Table 10-5. Fields Found in the
/etc/fstab File
|
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
ext2. |
|
Mount options |
A comma-separated list. |
|
Dump frequency |
For use with dump. |
|
Pass number for fsck |
Used at boot
time. |
10.2.3.2 Mounting and
unmounting
The following commands are used to mount and
unmount filesystems:
- 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.
10.2.3.3 Filesystem types
Common filesystem types compatible with Linux
include:
- ext2
-
The standard Linux
filesystem.
- iso9660
-
The standard CD-ROM format.
- msdos
-
The MS-DOS FAT filesystem.
- nfs
-
Remote servers.
- proc
-
The proc filesystem, which is a
system abstraction for access to kernel parameters.
- swap
-
Swap partitions.
- vfat
-
Virtual FAT, used instead of
msdos.
10.2.4 Objective 4: Set and View
Disk Quota
-
Quotas are used
to enforce a disk space or an inode maximum on individuals,
groups, or both.
-
These types of quota limits can be set:
- 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 filesystems:
 |
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.
| |
10.2.5 Objective 5: Use File
Permissions to Control Accessto Files
10.2.5.1 Access control
-
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 that
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 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.
10.2.5.2 Setting access modes
-
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 uses
the following syntax:
- chmod mode
files
-
Modify the access mode on files
using a symbolic or octal mode.
10.2.6 Objective 6: Manage File
Ownership
10.2.7 Objective 7: Create and
Change Hardand Symbolic Links
-
A link is a
pseudonym for another file.
-
Links take very little space in the
filesystem.
-
A symbolic
link is a tiny file that
contains a pointer to another file. Symbolic links can span
filesystems.
-
A hard link
is a copy of a file's directory
entry. Both directory entries point to the same inode and
thus the same data, ownership, and permissions.
ln has the following syntax:
- ln file
link
- ln files
directory
Create link to file or in
directory for all files. Symbolic links are
created with the -s option.
10.2.8 Objective 8: Find System
Files and Place Filesin the Correct Location
-
The FHS is used
by Linux distributions to standardize filesystem layout. It
defines two categories of data use, each with opposing
subtypes:
-
Data sharing:
sharable data can be used by multiple host systems on a
network. Non-sharable data is unique to one particular
host system.
-
Data modification: variable data is
changed continually by naturally occurring (i.e.,
frequent) processes. Static data is left alone, remaining
unchanged over extended periods of time.
-
The FHS seeks to define the filesystem
contents in these terms and locate information accordingly.
10.2.8.1 The directory
hierarchy
-
The root filesystem:
-
Must contain utilities and files
sufficient to boot the operating system, including the
ability to mount other filesystems.
-
Should contain the utilities needed by
the system administrator to repair or restore a damaged
system.
-
Should be relatively small.
-
/usr
contains system utilities and programs that do not appear in
the /root partition. It includes directories such as
/bin, /lib, /local, and /src.
-
/var contains varying data such as
printer spools and log files, including directories such as
log, mail, and spool.
10.2.8.2 Locating files
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