Joe Chung
Monmouth U. Homepage

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====== The Kernel, Tuning, Printing ======

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===== The Kernel and Kernel Configuration =====

  * The OS kernel provides interfaces to the following
    * Processes (time-sharing, protected address space)
    * Signals (to/from processes)
    * Interprocess communication (pipes and network connections) 
    * Virtual memory (swapping, paging, mapping)
    * Filesystems

  * The kernel contains device drivers and the rest is mainly device independent
    * Some kernels, such as proprietary UNIX kernels (Solaris, HP-UX, AIX, Mac OS X, etc.) usually run on hardware that is taylored to the OS, e.g. Solaris on Sun workstations/servers, Mac OS X on Macs.
       * Less portability but greater stability can be expected as a result.
    * Other kernels (Linux kernel, *BSD kernels, Windows) must deal with a wide variety of hardware, especially on Intel-compatible x86 platforms.
       * Greater portability but slighly less stability can be expected as a result.

===== When To Configure (Customize) a Kernel =====

  * Most systems come with generic kernel and kernel configurations that allows an OS to run on most supported hardware.
  * What to remove unneeded features and device support
    * not needed with modular kernels (such as that which accompany most Linux distributions)
  * Want to reconfigure to make kernel memory footprint smaller
    * Again, modular kernels make this unnecessary
  * Want to add third party or experimental device drivers
  * Want to add certain features
    * some intrusion detection and resistance systems
    * clustering
    * experimental file systems

==== Kernel Locations ====

    * Solaris - /kernel/unix
    * HP-UX - /stand/vmunix
    * Linux - /boot/vmlinuz-*
    * FreeBSD - /kernel 
    * Windows - ntoskrnl.exe

==== Kernel Configuration ====

    * Most operating systems provide some way to alter some behaviors of the currently running kernel.

    * Example: On linux, kernel behavior can be affected through the /proc file system if the kernel supports it.
          * The files in /proc aren't really files but "backdoors" into the kernel
          * One way to change the maximum number of open files a process can have on Linux:

                  # echo 179894 >> /proc/sys/fs/file-max

    * Example: On linux, the //sysctl// utility can be used to configure a running kernel's parameters.
      * Run //# sysctl -a// to see the kernel parameters that can be altered.
      * Also see /etc/sysctl.conf

==== Loadable kernel modules ====

    * Link to [[http://en.wikipedia.org/wiki/Loadable_kernel_module|article]]
    * Allows for adding & removing features or device support to a kernel core on an as-needed basis 
    * Finding currently installed kernel modules 
       * Solaris - modinfo
       * Linux - /sbin/lsmod 
         * Try //'lsmod | grep fs'// on your nfs servers.

==== Inserting and removing kernel modules ====

    * Solaris - add_drv/rem_drv, modload/modunload
    * Linux - insmod/rmmod, modprobe (like insmod but also handles module dependencies) 

==== Kernel Logging ====

    * Kernels usually log messages to the system log
    * Example: Linux //klogd// (Kernel Log Daemon) logs to /var/log/syslog
       * Also, the //dmesg// command gets info from "kernel ring buffer"
         * Can be useful to run //dmesg// to verify kernel module loading & unloading

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===== Performance Tuning and Benchmarking =====

    * Usually only concerned about performance tuning if the system or systems seem unusually slow or on really busy web sites whose web servers must handle many web transactions. 

    * The hardware may be too slow, antiquated.
          * You may have insufficient RAM to support a large number of simultaneous users.
          * You may have an insufficient number of CPUs to support a large number of simultaneous users.
          * You may have slow, highly fragmented or failing hard drives. 

    * A user or users may be running a very resource-intensive program that puts a large load on the system.
          * May need to set ulimits (//man ulimits// and /etc/security/limits.conf).
          * Or write //cron// jobs to find resource hogs and //renice// them down. 

    * A file system may be slow.
          * May need to tune FS configuration
                * Most file systems allow turning off access time stamp (atime) updates which can speed up file & directory access.
          * May need to choose a different FS.
                * Some file systems are better suited to accessing very large files, others are better suited to accessing many small files.

    * A networked file system (NFS, Samba or other) may seem unusually slow.
          * If NFS or Samba are much slower than ftp, may need to tune configuration.
                * Samba config example: enable "opportunistic locking," disable "strict locking"

    * A network or network applications are slow.
          * Prime suspect: DNS (domain name system)
                * A network name server may have died.
                     * rockhopper:/etc/resolv.conf

    * Some performance tips for UNIX / Linux that I have seen:
          * Try to put the swap partition as close to the start of the disk as possible (lower cylinder and sector numbers).
          * Try to make sure that the swap partition disk is on a different disk controller than the data disk.
                * or stripe swap across multiple disks for better write performance.
          * Compile the kernel, services and programs with optimizations that take advantage of > i386 CPUs and their specialized instruction sets, e.g. Pentium*, Athlon*.

    * Benchmarking
          * Can be ad hoc such as applying the //time// command to a long process, such as a kernel compile
          * Various benchmarking programs exist
             * Some we can try in lab:
                   * Disk I/O - iozone (http://www.iozone.org), iostat
                         * Can be used to benchmark local disk or NFS server performance 
                   * Network - NetPIPE (http://www.scl.ameslab.gov/netpipe), tbench
                   * System - nbench (http://www.tux.org/~mayer/linux/bmark.html ), geekbench (http://www.primatelabs.ca/geekbench)


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===== Printing =====

  * Steps to set up a local printer on a UNIX system
    * Physically connect the printer to the computer (usually through the parallel port or USB)
    * Configure the proper files on the system to communicate correctly with the proper port
          * kernel needs support for parallel port
    * Create a spooling directory and accounting files for this print queue
    * Set up proper filter programs (if necessary)
    * Configure the printer system to allow printing to your new device
    * Enable printing on the new device
    * Send a print job to test the printer
    * Most of the above steps might be automated using print config utilities
          * printconf on RedHat and derivatives
          * admintool and others on Solaris 

  * BSD printing
    * The lpr system uses a single printer capabilities file to control printing
          * Which device, what filter to use, baud rates, form feeds, remote host and remote device name, etc
          * The lpr system can work over a network 
    * lpr - queues print jobs
    * lprm - removes print jobs form queue
    * lpq - shows jobs in print queue
    * lpc - printer control program
    * lpd - printer daemon
    * /etc/printcap - printer configuration file describing all printers on this host (and possibly other remote hosts) 
    * BSD printcap file
          * See /etc/printcap on rockhopper

  * System V printing
    * The lp system uses scripts that control the printer devices. (System V.4 adds remote printing and Postscript capabilities)
       * lp - initiates print requests
       * cancel - cancels pending print requests
       * lpstat - to list queue contents and show status
       * accept - allows lp to accept requests
       * reject - prevents lp from accepting requests
       * enable - activates named printer
       * disable - disables named printer
       * lpadmin - configures lp spooling system
       * lpsched - line printer scheduling daemon
       * /usr/spool/lp/model - directory where model files are kept 

  * Postscript in UNIX printing
    * Most UNIX utilities and applications that deal with output to a printer will output Postscript.
    * See some sample Postscript output with //gv or ghostview//

  * CUPS (Common UNIX Printing System)
    * Dominant printing system on Linux now
    * Also used in Mac OS X
      * CUPS is developed and owned by Apple.

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===== Lab Activity =====

==== Compile, install and run a new Linux kernel ====

  * Download, configure, compile custom Linux kernel in the "Debian" way on your Linux VM.
    * Do this on only one of your VMs.
    * Requires the //build-essential//, //kernel-package// and //libncurses5-dev// packages.
    * Download a kernel-source archive from the instructor-supplied URL.
    * Extract kernel source from the tar.bz2 archive in /usr/src:

         # tar xjf linux-source*.tar.bz2

    * Apply existing kernel configuration from /boot:

         # cd /usr/src/linux-source*
         # cp /boot/config-3.2.something* .
         # cp config-3.2.something* .config

    * Do minimal configuration of kernel using //make menuconfig// in the kernel source directory:
      * Change processor (CPU) type
      * Make sure there is kernel support for the following:
        * file system support for: ext2, ext3
        * device driver support for:
           * All related to SATA disk drives
              * See output of //lspci -v//
      * Save new kernel config as //vanilla471//
        
    * Compile kernel using //make-kpkg//:

         # nohup make-kpkg --revision=vanilla471 --initrd kernel_image &

    * Install new kernel linux-image kernel package found in /usr/src:

         # dpkg -i /usr/src/linux-image*.deb

    * Check GRUB boot loader config (/boot/grub/grub.cfg) to ensure that the new kernel will be booted by default.

    * Reboot the VM.

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==== Set up CUPS printing ====

  * Set up remote printing to hh310
    * We will set up networking printing to the HP Laserjet 4200 in HH 310 using CUPS, the Common UNIX Printing System, which is now a de facto standard for Linux printing.
    * Ssh to your VM as root using ssh -X (X11 forwarding).
    * Install //iceweasel// (Debian equivalent of firefox) and //hpijs-ppds// packages
    * Run iceweasel remotely on your VM.
    * In iceweasel, visit the CUPS administration web interface at the following URL and add a printer with queue name "hh310":

            http://localhost:631
      
    * The CUPS printer URL for the printer in HH 310 is

            socket://10.8.0.119:9100
  
             where :9100 is the HP Jetdirect service port for the
             Jetdirect network card in the printer.

    * Choose the correct printer model (or as close as possible), and choose the Postscript driver for it.
    * Make "hh310" the default printer.
    * Send a test page to the printer.
    * Try printing something with //lpr// and a HERE document.

             # lpr << END
             This is a test from root@carson.cs.monmouth.edu.
             END

    * Try printing something with //enscript// (may need to install enscript first) and a HERE document.

             # enscript << END
             This is a test from root@carson.cs.monmouth.edu.
             END

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===== Leftover Lab Activities =====

  * These are NOT [[cs_471_tasks|mandatory]].

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==== One-to-many copying of large files using bittorrent ====

  * Start by installing either the //bittorrent or bittornado// package.
  * Try to write a script called //btcp// that automates the process of:
    * setting up a bittorrent tracker on the source machine
    * creating and uploading a torrent file from the source machine to the target machines
    * seeding the torrent on the source machine
    * downloading the torrent on the target machines

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==== The Spamassassin Mail Filter ====

  * Install, configure and test spamassassin.
    * Start by looking at /etc/default/spamassassin.

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==== Firewalls with iptables ====

  * Try blocking and unblocking outgoing port 80 (www) from your VM.
  * Try blocking and unblocking incoming ssh connections from a specific IP address.

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