Linux and Parallel computing

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Linux and Parallel computing

• Stefano Leonardi

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Why linux

• General purpose operating system
• Focused on the latest open source technology
  (zero license cost)
• Rapid 4 to 6 months release cycle
• Available for free download (www.linuxiso.org)
• Limited support, but a lot a FAQ forums
• Advantages more stable than windows, sources
  available, closer to the computer language (than
  faster). MULTITASKING.
• Disadvantages less user friendly, less
  applications, difficult to install mp3 players or
  chat.

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Commercial version?

• Red Hat Enterprise Linux focused on mature Open
  Source Technology Scalability, stability,
  performance, availability.
• 24x7 coverage plans available

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Installation

• You can install in your laptop both LINUX and
  WINDOWS
• Installation procedure is becoming user friendly.
  Auto probe does all the job.
• You have to partition your DISK! IMPORTANT IF YOU
  MAKE A MISTAKE YOU CAN LOOSE YOUR DATA.

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DISK PARTITIONING

• Disk structure
• Master boot record
• Standard partition table
• Primary partition (4)
• Extended and logical partition
• Disk Druid at install, fdisk post install

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/dev/hda Eide disks /dev/sda Scsi disks

• A partition is a device. /home is a mount point,
  just a label. If /dev/hda2 is mounted as /home,
  if I reboot and mount /dev/hda2 as /home2 Ill
  have the content before in /home now in /home2.
• Is not like windows, every time you boot you have
  to associate a partition /dev/hdaX to a mount
  point (there is a file you can edit /etc/fstab)

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Why separate file systems?

• Flexibility, containment, quotas, recovery
• / is the root filesystem. Used as the base
  directory
• /boot partition to avoid conflict with 1024
  cylinder limit.

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Boot Sequence

• BIOS INITIALIZATION (common to all OS)
• Peripherals detected
• Boot device selected
• First Sector of boot device read and executed
• Boot loader (LILO or GRUB) loads the operative
  system (divided into 2 stages, one small which
  has the task to locate and start the second stage
  boot loader which really loads the OS). The first
  stage is usually in the MBR and it is about
  500K.You can choose different OS to start.
• Kernel initialization (kernel contains the
  drivers to initialize and use the devices (such
  as a disk) messages are in /var/log/dmesg modules
  can be included in initrd image.
• Init reads its config (/etc/inittab) and loads
  first processes

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File systems

• To create a filesystem first change the partition
  table with fdisk (es. Fdisk /dev/had)
• Then create a filesystem with mkfs.ext2-mkfs.ext3
• Several filesystem type in linux (difference with
  windows) ext2-ext3-vfat-swap are the most common
• Mount point

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RAID

• Redundant Array of Inexpensive Disks
• RAID0 (no redundancy)
• RAID1 (mirror)
• RAID5 (use 5 disks, one is for parity)
• With fdisk creates partitions linux raid type
• Then, create a file where you specify the RAID
  type and the partitions you want to use
• Then, mkraid /dev/md0
• Activate raid on each partition (raidstart
  /dev/md0)
• Create a filesystem mke2fs j /dev/md0
• Mount it

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Recovery

• Recovery from a broken disk.
• Replace the fallen hard drive
• Reconstruct partitions on the replacement drive
  raidhotadd /dev/md0 /dev/sda1

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Users

• Linux is multi-users
• Command w and last
• Useradd username
• Passwd username
• Then you can create groups (groupadd) and gives
  privileges to groups (i.e. write or read on
  particular disks)

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Users environment

• /etc/skel
• /etc/profile (first one to be executed)
• /etc/profile.d (contains script)
• /etc/bashrc (blobal aliasis system settings)

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Quota system

• Start or stop quotas quotaon, quotaoff
• Edit quotas edquota username

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Network

• /ets/sysconfig/network
• Gateway
• DNS
• IPADDRESS
• DHCP

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Network File System

• A disk can be on a remote machine and be used.
  The system where the Hard Disk is located needs
  to give privileges to export the filesystem.
  This is in the file /etc/exports. For example,
  usually in a cluster, you want to have the same
  home on all the nodes, this is done with the
  export command.

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TCP/IP WRAPPER

• You can allow access to some machines and deny
  access or services to others

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SAMBA

• It is a server to share resources with Windows
  (i.e. printers). If you have a printer installed
  in linux, you can allow a windows user to use it
  (you have to create the user and passwd).

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Secure connections

• When Argentina was still good in football (ages
  ago) we used telnet and ftp.
• With this servers the passwords travel encrypted
  so easily to be sniffed by hackers.
• We use now ssh and scp.
• There are free ssh and scp servers for windows
  that allow you to communicate with linux machines
  (putty).