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Unix Administration 4


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  • 1. ITI-481: Unix Administration Rutgers University Center for Applied Computer Technologies Christopher Uriarte, Instructor Meeting 4
  • 2. Today’s Agenda
    • Disk Partitioning
    • Directories and File Systems
    • Mounting Local File systems
  • 3. Disk Partitions.
    • A typical UNIX installation will divide one or more hard drives into multiple partitions.
    • In Linux, each disk is given its own device name: /dev/hdX (X can range from a-z) – IDE disks /dev/sdX (X can range from a-z) – SCSI disks
    • A partition number is added to the device name: /dev/hdXY (Y is the partition number) – IDE disks /dev/sdXY (Y is the partition number) – SCSI disks For example, the first partition on the first IDE drive on a system would be /dev/hda1 .
    • Disk partition information can be viewed using the ‘df’ command.
  • 4. Understanding File System Types
    • Different operating systems use different file systems.
    • A file system type is essentially the “specification” for how blocks of data are organized on disks.
    • Some file systems have features that other file systems may not have, such as the ability to more easily handle corrupted data or system crashes.
  • 5. Some Common File System Types:
    • FAT – used with DOS, Windows 3.1, Windows95, Windows98
    • FAT32 – used with Windows98/SE, WindowsME an some Windows95 distributions. Can also be used on Windows NT,2000 and XP.
    • NTFS – used on Windows NT, 2000 and XP
    • UFS (Unix File System) – a generic UNIX file system used on many UNIX flavors.
    • EXT2 – a Linux-specific file system used in most Linux distributions
    • JFS, ReiserFS, EXT3 – next-generation advance file systems available as an option on some UNIX systems today. (actually, all are available for Linux)
  • 6. Selecting a File System Type
    • Linux is unusual, as it allows you to choose the file system type of a partition during setup.
    • Most UNIX’s use their default file system type during install (usually UFS).
    • Linux, however, has the flexibility to create and mount many different file system types, although we generally use EXT2, as it’s the most Linux-compatible. (remember, EXT2 is the Linux default)
  • 7. Partitions and File Systems: A Recap
    • (From Class 1) Disk Partitioning is the concept of dividing your hard disk into logical partitions, making one hard drive appear as if it’s actually multiple drives.
    • There’s several reasons why we partition disks:
      • Performance
      • Ease of storage management
      • Security
  • 8. Disk Partitioning in UNIX
    • In UNIX, a physical disk partition is associated with a directory path, sometimes referred to as a mount point .
    • All files that are in directories associated with a mount point are stored on the mount point’s physical partition.
    • If a directory path is not explicitly associated with a physical disk partition, its files are stored under the root ( “/” ) partition.
  • 9. UNIX Partition Example /usr 2GB / (root) 1.5GB /home 4GB swap Example Partitioning Scheme: Total Hard Drive Space: 8GB Contains all files under the /usr directory (I.e. /usr/local/bin/pico, /usr/bin/vi, etc.) Contains all files under the /home directors (I.e. /home/chrisjur, /home/iti1234) Contains all other files and directors, such as /var, /opt, /sbin, etc. [HARD DRIVE]
  • 10. Disk Partitioning: Rules to Live By
    • Making disk partitions is easy; Changing them can be hard.
    • It’s not often easy to expand or shrink disk partitions (in fact, it’s impossible to do on many operating systems), so make sure you have adequate space for your data storage.
    • You can always create partitions from new hard drive.
    • You can always create partitions from un-partitioned space on existing, in-use hard drives.
  • 11. Example: Adding a Partition Using Un-partitioned Space /dev/hda1 Mounted on /home (Unused) /dev/hda1 Mounted on /home /dev/hda2 Mounted on /home2 You can easily take unused hard disk space, format it, partition it and mount is as a new file system.
  • 12. Steps Required Make a New Partition
    • Partition empty space on the hard drive
    • Format the newly created partition
    • Create a mount point for the partition
    • Mount the partition
  • 13. Partitioning Empty Hard Drive Space
    • Empty hard drive space can be partitioned using a utility called fdisk.
      • Fdisk allows you to create, delete and modify partitions, as well as to set their partition types.
      • Allows you to print the partition table for a particular hard drive.
    • Can be started with: /sbin/fdisk <hard drive to edit>
      • e.g. /sbin/fdisk /dev/hda
  • 14. Fdisk: Sample of Help Menu
    • # /sbin/fdisk /dev/hda
    • Command (m for help): m
    • Command action
    • a toggle a bootable flag
    • b edit bsd disklabel
    • c toggle the dos compatibility flag
    • d delete a partition
    • l list known partition types
    • m print this menu
    • n add a new partition
    • o create a new empty DOS partition table
    • p print the partition table
    • q quit without saving changes
    • s create a new empty Sun disklabel
    • t change a partition's system id
    • u change display/entry units
    • v verify the partition table
    • w write table to disk and exit
    • x extra functionality (experts only)
  • 15. Example: Creating a New Partition with Fdisk
    • Launch fdisk – edit hard disk /dev/hda: > /sbin/fdisk /dev/had
    • Type “p” to print the current partition table.
    • You can now create a new partition, specify the size of the partition and then specify its file system type.
    • The “n” option will allow you to add a new partition. You are prompted to specify whether you want to use a primary partitions 1 to 4) or logical partition (partitions 5 and above). You should choose “p” for primary partition.
    • You will be asked to specify a partition number. Refer back to the partition table -You can choose a partition number that is not used from 1-4.
  • 16. Creating Partitions, con’t
    • You will then be asked to specify the starting cylinder – simply choose the default.
    • You will then be asked to specify the size of your new partition. You can specify this size in cylinders, kilobytes or megabytes (e.g. +1500M makes the partition 1500MB).
    • You must now specify the partition’s file system type by using the “t” option. Typing “L” will list the partition type codes. You want to use type 83 – Linux native.
    • Finally, type “w” to write the new partition table and exit – you may have to reboot.
  • 17. Step 2: Formatting the new File System
    • Assuming you just created partition #3 on /dev/hdb, the partition you just created is now called /dev/hdb3. You must now format that partition.
    • Partitions are formatted using the mkfs command. There is a special mkfs, called /sbin/mkfs.ext2 , used to format Linux EXT2 file systems.
      • Usage: /sbin/mkfs.ext2 <partition to format>
      • e.g. /sbin/mkfs.ext2 /dev/hdb3
  • 18. Step 3: Choosing and Creating a Mount Point
    • Now that you have a fresh chunk of useable disk space, you need to decide how you will access it.
    • You must choose a unique and empty directory path to be associated with your partition – this is referred to its mount point.
    • For example, if you’ve created a partition /dev/hdb2, and you want to access its disk space via the path /newdisk, you must first create the path /newdisk (“mkdir /newdisk”) and we must then mount the partition on that path.
  • 19. Step 4: Mounting the New Partition
    • After choosing and creating a mount point, you can mount the partition using the UNIX mount command:
      • mount [options] <partition> <mount point> For example: mount –t ext2 /dev/hdb3 /newdisk
      • ( -t specifies file system type)
    • After mounting the file system, you are now ready to use it!
  • 20. Viewing Mounted File Systems
    • You can view mounted file systems using the “df –k” command:
    • Filesystem 1k-blocks Used Available Use% Mounted on
    • /dev/hda5 3309736 913788 2227820 29% /
    • /dev/hdb1 495204 13 469623 0% /home
  • 21. Unmounting File Systems
    • File systems are unmounted with the umount command:
      • umount <mount point>
      • For example: umount /newdisk
    • File systems should only be unmounted when they are not in use.
  • 22. Typical Directory Structure
    • Note: Not all directory paths have their own partitions – in fact, a system may only have 1 partition!
    • / - begins the file system structure (root)
    • /boot - kernel files
    • /usr – scripts and binary applications
    • /sbin – basic system tools
    • /home – user home directories
    • /var – log files and other time sensitive data
    • /etc – configuration files
    • /dev – device drivers
    • /opt – typical install location for some commercial software
    • /tmp – temporary storage
    • /mnt – mount points for floppy disks and CD-ROMS
    • swap – swap space
  • 23. Sample Directory Tree with Mount Points
  • 24. /etc/fstab
    • Specifies what partitions to mount automatically during boot time.
    • Entry format: < partition> <mount point> <fs type> <parameters*> <fs_freq*> <fs_passno*> Sample entry: /dev/hda3 /newdisk ext2 defaults 1 2
      • *These fields are usually set to defaults, 1 and 2, respectively.
    • For entries in /etc/fstab, you can run mount command with just mount point: > mount /tmp To mount all file systems in /etc/fstab: > mount -a
  • 25. Exercises/Problems
    • How do you rename a the mount point associated with a partition? (I.e. change the mount point for /dev/hdb3 from /newdisk to /home?)
    • What do you do if you’re running out of disk space on a new partition?
    • What do you need to do after you’ve added a new hard drive?
  • 26. Homework
    • As Assigned in class…