~  CHAPTER 8:    FILE SYSTEMS  ~

 

 

Linux is built upon the foundation of file systems.  They are the mechanisms by which the disk gets

organized, providing all of the abstraction layers above sectors and cylinders. 

By default Linux file system , ext2.

 

 

i-Nodes

 

The most fundamental building  block of many UNIX file systems (including Linux’s ext2) is the i-node.

/usr/src/linux/include/linux/ext2_fs.h

 

 

Superblocks

 

The very first piece of information read from a disk is its superblock.

This small data structure reveals several key pieces of information, including the disk’s geometry,

the amount of available space, and most important, the location of the first I-node.

Without a superblock the file system is useless.

 

 

Ext3 and ReiserFS   (very quick in class)

 

As of this writing, the ext2 file system is somewhere around seven years old.  This means two

things for us as system administrators:  First and foremost, ext2 is rock solid.

 

 

Mounting and Unmounting Local Disks

 

Partitions are mounted so that they appear as just another subdirectory.

The file-system management process begins with the root directory.

Keep in mind that a new directory is mounted, the mount process hides all the contents of the

previously mounted directory.  So in our /usr, if the root partition did have files in /usr before

mounting /dev/hda3, those /usr files would no longer be visible.  (They’re not erased, or course –

once /dev/hda3 is unmounted, the /usr files would become visible once again).

 

 

 

======================================================================

 

linux8.html                                                      PAGE 2                                                      2002/07/17

 

 

 

Using the mount Command

 

Like many command-line tools, the mount command has a plethora of options, most of which

you won’t be using in daily work.

mount^-a and umount^-a

 

 

Using fsck

 

The fsck tool, short for File System Check, is used to diagnose and repair file systems that may

have become damaged in the course of daily operations.

Usually, the system runs the fsck tool automatically during the boot process (much in the same

way Windows runs Scandisk) if it detects a partition that was not cleanly unmounted.

 

NOTE:  fsck isn’t the proper title for the ext2 repair tool; it’s actually just a wrapper.  The fsck

wrapper tries to determine what kind of file system needs to be repaired and then runs the

appropriate repair tool, passing any parameters that were passed to fsck.  In ext2, the real tool

is called e2fsck.  When a system crash occurs, you may need to call e2fsck directly rather than

relying on other applications to call it for you automatically.

 

 

Where Disks Exist

 

Under Linux, each disk is given its own device name.  IDE disks start with the name /dev/hdX,

where X can range from a through z, with each letter representing a physical device.

 

NOTE:  It is acceptable to partition a disk so that only one large partition is taking up the entire

disk.  But beware:  If this is the boot partition, the entire partition must fit within the 1024

cylinder boundary, or you will not be able to boot.

 

IDE = hd

SCSI = sd

 

       ./fdisk/dev/had (enter hda = primary and you can have a maximum of 4

 

 

 

 

======================================================================

 

linux8.html                                                      PAGE 3                                                      2002/07/17

 

 

 

Making File Systems

 

With the partitions created, we need to put file systems on them. 

Under Linux, we use two tools for this process:  mke2fs to create ext2 file systems, and

mkswap to create swap file systems.

 

 

Network File Systems

 

Network file systems make it possible for you to dedicate systems to serving disks while

letting clients handle the compute-intensive tasks of users.

 

 

Mounting NFS Partitions

 

 

Mounting NFS partitions works much the same way as mounting local partitions. 

Originated from Sun Micro Systems.

 

In NFS mounts, partitions are referenced by their hostnames and export directories.  Thus,

if the server named technics is allowing your host to mount the directory /export/SL1200/MK2

and you want to mount this to /projects/topsecret1, you would use this command:

 

mount^technics:/export/SL100/MK2^/projects/topsecret1

 

 

Automounts are similar to a small peer-to-peer network.

Alternatives to Linux Automounter.  AMD for Auto-Mounter Daemon.  What made AMD so

popular was that it was the first truly cross-platform Automounter tool.

 

 

Quota Management

 

In any multiuser environment, you’re bound to run across users who either refusing to play fair

or because they’re oblivious to common courtesy, practice the fine art of disk hogging, taking

up more than a reasonable amount of space. 

Set up disk quotas.

 

/etc/fstab file you must edit it.

 

You must enable Quotas  you must have the files quota.user and quota.group.

 

 

 

 

 

======================================================================

 

linux8.html                                                      PAGE 4                                                      2002/07/17

 

 

 

 

Configuring Quota Settings

 

Soft Limit.  This requested limit is placed on a user or group.

Hard Limit.  This limit is imposed by the operating system and cannot be overrun.

Grace Period (Time Limit).  When a user’s account exceeds the soft limit, a clock starts tracking.

 

 

Command-line Options of edquota

 

When you invoke the edquota command, it brings up the configuration information for the

particular user, group or grace period you want to add or edit.  By default, the vi editor is

used to display human-readable information.

 

 

Managing Quotas

 

·        quotacheck

·        repqutota

·        quota

·        quota^-v

 

Summary:

 

will be executed.