Devices, Linux Filesystems,and the Filesystem Hirarchy standard

1
Devices, Linux Filesystems,and the Filesystem
Hirarchy standard
2
Objectives

• Create Partisions and Filesystems
• Maintain the integrity of filesystems
• Control filesystem mounting and unmounting
• Set and view disk quotas
• Use file premissions to control access to files
• Manage file ownership
• Create and change hard and symbolic links
• Find system files and place files in the correct
  location

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Disk Drives Under Linux

• Linux supports all sorts of drives and file
  system types
• The two most widley used types are IDE and
  SCISI
• IDE Intergrated Device Electronics drive.
• SCSI ( pronounced scuzzy) , Small Computer
  System Interface drive.

4
Hard disk devices IDE

• /dev/hda primary Master
• /dev/hdb primary Slave
• /dev/hdc Secondary Master
• /dev/hdd Secondary Slave
• These may change in the future as the politicaly
  correct are trying to do away with the terms
  Master and Slave...

5
Hard disk Drives SCSI

• /dev/sda first SCSI drive
• /dev/sdb Second SCSI drive , sdc,sdd,sde , and so
  on ...
• Can be up to 15 devices on a single interface ,
  most of the innards are on the interface card
  where under IDE the innards are on the drive
  itself.
• SCSI are typlicaly more expensive and
  considered more reliable and are used on servers
  and workstations , where IDE's are typicaly found
  on desktop machines .

6
Disk partitions

• Disk can contain up to 16 partitions.
• The drive partition is expressed as a number
  after the drive name , such as /dev/hda1 for
  the first partition on the primary master drive.

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Partition Types

• Primary - This type contains a filesystem, up to
  four may exist. One must be marked as active and
  contain the operating system so the BIOS can find
  and load it at boot time.
• Extended a varient of the primary , a
  container for logical partitions. Only one per
  disk.
• Logical from 1 to 12 logical partiitions can be
  created , logical partitions are numbered from 5
  to 16.

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The root filesystem and mount points

• / - the root directory
• /bin and /sbin - Contains system binarys.
• /etc configuration files.
• /lib - program libraries.
• /boot - Kernal images and other files used to
  boot the system.

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Mount points cont...

• /home user files area.
• /temp temporay files space
• /var log files
• /usr user commands , source files ,
  documentation, ect...
• /swap used to enable virtual memory.

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Managing Partitions

• Fdisk device
• Example to work with the primary master drive
  the command fdisk /dev/hda would be used ,
  that by the way is also the default , if no drive
  is invoked.
• Swiches , a ,d,l,m,n,p,t,w
• Demonstration of fdisk

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Creating Filesystems

• Mkfs -t fs_type fs_options device
• Where fs_type is one of the supported file
  systems like msdos or ext2 or ext3
• And fs_options , see man pages for options
• Device - the partitision you want to work on
• - mksf is like format command in DOS..

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Swap files

• Syntax mkswap device
• Such as mkswap /dev/hdb3 for make a swap
  partitition on the first IDE interface , Slave
  drive, partition number 3 please ...

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Maintain the integrity of filesystems

• Monitor free disk space and Inodes
• Monitor disk usage
• Checking filesystem integrity

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Df command

• Syntax df options directories
• df command gives information about disk
  space and inode utilization.
• Options , -h information about space , -i
  information about inodes.
• df -h /dev/hda , tell me about the space on
  the primary master drive ....

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Du Command or Disk Utilization

• Syntax duoptionsdirectories
• -a , shows all files , not just directories.
• -c, grand total.
• -h , produces out put in a form that us lowly
  humans can understand !
• -s , prints summery
• -S, Excludes subdirectories from count and
  totals.
• Example

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Checking Filesystem Integrity

• Filesystems can become scrambles because of power
  failure and othere things.
• The fsck program allows you to restore the
  superblock with a good copy.
• Syntax fsck-t type fs-options filesystem
• Example fsck -f /dev/hda5

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Controling Filesystem Mounting and Unmounting

• Each filesysyem is mounted as a directory to the
  root file system.
• To automaticaly mount filesystems at boot time
  use the /etc/fstab file .
• The fstab file tell the kernal what and
  where the filesystems are and how they are to be
  used.

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Managing fstab

• There are 6 fields that make up each line in the
  fstab file. Each field preforms a different
  function.
• Device, mount point, Filesystem type , mount
  options , Dumb frequency and pass number .
• Example

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Mounting Filesystems

• The Mount command is used to mount filesystems.
• Syntax
• mount command_line_options device derectory
• Example to mount a cdrom
• Mount -t iso9660 /dev/hdc /mnt/cdrom

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Unmounting a filesystem

• Command umount options device directory
• Example umount /cdrom or umount /dev/hdc

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Quotas

• Per-user hard limit
• Per-user soft limit
• Per-group hard limit
• Per-group soft limit
• Grace period

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Quota Commands

• quota -u -g options user group
• Displays quota limits.
• Qutaon options filesystems
• Turns on Quotas.
• Quotaoff options filesystem
• Turns off Quotas.
• Quotacheck options filesystems
• Compiles quota databases , should be run weekly
  via cron.

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Quota Commands cont.

• Edquota -p proto-user options names
• Used to edit quotas for users and groups , it
  uses vi editor . It is interactive .
• Repquota options filesystems
• Used to report quotas for users and groups

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Enabling Quotas

• Set options in /etc/fstab , add userquota and
  grpquota to the default options.
• Create a quota.user and quota.group files at
  the top of the /home filesystem and make it a
  root access only.
• Run quotacheck to make the database.
• Run quotaon to enabel the quota system.
• Check to see if it's starting up in your init
  script at boot.
• Make a cron job to run quotacheck.

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Use File Permissions to control access to files.

• Three Classes of users
• User The user that owns the file.
• Group The group that owns the file.
• Other All others users on the system.

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File Permissions

• Read , mnemonic r , examine contents of file
  and list directory contents.
• Write , mnemonic w , Write to or change the
  file and create and remove files in the
  directory.
• Execute , mnemonic x , run the file as a
  program also read and write files in a directory.

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File permissions cont.

• From left to right user, group, other
• Mnemonic are used to indicte tru and -
  indicates false.
• Rw-rw-r--
• User has read write permissions ,group has read
  write permissions and others have only read
  permissions.

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SUID , SGID and Sticky

• SUID(Set User ID) is for executable files only ,
  if the SUID bit is set the files owner owns the
  resulting process , no mater who launched the
  program.
• SGID(Set Group ID) works the same for groups as
  SUID does . When set on a directory all files
  created inside that directory belong to the
  group.
• Sticky keeps a program in memory after execution
  . When used in a team inviroment it allows
  groups to create and modify files but only file
  owners can delete or rename them.

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Setting Access Modes

• Umask, used to set initial file modes for a shell
  session.
• Chmod , changes mode of a file
• Chmod options symbolic_mode ... files ,
  example chmod urw,gow aflie
• chmodoptions octal_mode files, example chmod
  666 afile
• Chmod r afile , makes it readable for all
  class of users ...

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Manage file ownership

• Use chown and chgrp
• Chown can be used to change both user and group
  of a file .
• Chown options user-owner files
• Chown options user-owner.group-owner files
• Chown options .group-owner files
• Chown options referencerfile files , uses
  rfile as a template for permissions of files .

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Hard and symbolic links

• A link is pseudofile that creats a shortcut to a
  file.
• Symbolic links are tiny flies that contain a
  pointer to another file.
• Hard links are not realy a link but a copy of
  another directory entry. Two directory entries
  have different names but point to the same inode

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Link commands

• Ln creats a link
• Ln options file link
• To find the file pointed to by the link use the
  ls -l command.

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Finding files and placing them in the proper
location

• Locating files , commands..
• Which , example which tcsh
• Find
• Locate
• Updatedb
• Whatis
• Apropos