Differences

This shows you the differences between two versions of the page.

--- notes:lpic-1_notes [2014/02/09 22:24]
smthng
+++ notes:lpic-1_notes [2014/03/02 22:01]
smthng [102 Installation and Package Management 18%]
@@ Line 16: / Line 16: @@
   * Conceptual understanding of sysfs, udev, hald, dbus
   * Terms: /sys, /proc, /dev, modprobe, lsmod, lspci, lsusb
+== Notes ==
+  * BIOS - Basic I/O System - systim init, memory testing, low-level system-config, OS boot order (CD, floppy, HD, PXE), internal HW clock
+  * /proc fs is kernel's status repository: interrupts, dma, ioports
+  * Universal Serial Bus (USB)
+    * //lsusb [-t] [-vv] // - t-tree view, vv-very verbose
+    * Open Host Controller Interface (OHCI) - USB 1.1
+    * Universal Host Controller Interface (UHCI) - USB 1.1 - 12 MBps - low+full speed
+    * Enhanced Host Controller Interface (EHCI) - USB 2.0 - 480 MBps - high speed
+    * Extensible Host Controller Interface (XHCI) - USB 3.0 - 4 GBps - super speed
+    * Wireless Host Controller Interface (WHCI) - Wireless USB 1.0 - 480 MBps
+    * Effective speed is lowest speed of device, cable and hub
+    * Classes of USB devices :
+      * Human Interface Device (HID) - Input devices: mice, keyboards, etc.)
+      * Communications device - Modems
+      * Mass storage device - Disk devices, flash readers, etc.
+      * Audio - Sound devices
+      * IrDA - Infrared devices
+      * Printer - Printers and USB-to-parallel cables
+    * Linux kernel supported USB in v2.3.x, backported to 2.2.18
+    * Linux drivers may be host controller drivers (e.g. usb-ohci.o), class drivers (e.g. hid.o, usb-storage.o, printer.o, audio.o) or device-specific drivers
+    * usbcore.o -> host controller driver -> class/device driver
+    * Modularized USB drivers are loaded by the generic /sbin/hotplug kernel support
+  * //lsdev// - shows hardware including IRQ info, I/O ports and DMA channels
+  *  //lspci [-t] [-vv]// - info about system’s PCI buses and installed PCI devices
+  * A module is dynamically linked into the running kernel when it is loaded
+    * //insmod/rmmod// - insert/remove mocule, no dependency checking
+    * //modprobe [-r] [-a] [-t type]// - list, insert or remove modules. Does dependency checking.
+    * //lsmod// - list modules //modinfo module-object-file.o// - info about a module file
+  * sysfs is a RAM-based filesystem derived from ramfs. It provides a means to export kernel data structures to  user space. // mount -t sysfs sysfs /sys//
+  * The udev process uses sysfs info to create dynamic device files as kernel modules are loaded. /etc/udev.d holds rules to be applied when adding or removing a device.
+  * D-Bus is an IPC system that uses sysfs to implement a message bus daemon used for broadcasting system events e.g.“new device added” or “printer queue changed”.
+  * hal was a hw abstraction layer (hw access API) on top of udev using D-Bus. It has been deprecated and rolled into udev and the kernel.
 ===  101.2 Boot the System (LCN-4 CTL-5) ===
@@ Line 22: / Line 56: @@
   * Check boot events in the log file
   * Terms: /var/log/messages, dmesg, BIOS, bootloader, kernel, init
+== Notes ==
+  * Boot Loader (LILO or GRUB) launches the linux kernel, passing kernel parameters if needed (/etc/lilo.conf | /boot/grub/menu.lst | /boot/grub/grub.conf)
+  * Module options (as well as aliases and post-install and pre-remove actions) are stored in /etc/modules.conf .
+  * //dmesg// displays kernel messages logged at last system boot.
+  * // /var/log/messages // contains all syslog messages.
 === 101.3 Change runlevels and shutdown or reboot system (LCN-4 CTL-5) ===
@@ Line 31: / Line 71: @@
   * Knowledge of basic features of systemd and Upstart
   * Terms: /etc/inittab, shutdown, init, /etc/init.d, telinit
-<pagebreak>
+== Notes ==
+  * When linux boots, first process is the //init// process which selects and switches to default runlevel.
+  * Runlevels - 0=shutdown, 1/s/S=single-user_maintenance, 2=multi-user, 3=multi-user_no-X, 5=multi-user_with-X 6=reboot
+  * On Debian, 2 is default and 3,5 are not used. On Redhat, 3 is the default.
+  * /etc/rc script to change runlevels on redhat (also init/telinit script)
+  * /etc/rc.sysinit (Redhat) or /etc/init.d/rcS (Debian) - system init script launched by init before system daemons
+  * /etc/rc.local- local startup actions called at end of startup
+  * /etc/init.d contains startup/shutdown scripts for all system services
+  * /etc/rc0.d - /etc/rc6.d contain softlinks KNNservice or SNNservice specifying whether to start or stop services and in what order for that runlevel (done by init process). Kills done before starts.
+  * /etc/inittab contains "id:N:initdefault:" for default runlevel N
+  * //runlevel// shows current and previous runlevel
+  * //shutdown [options] time [warning message]//  - -f=fastboot -h=halt -r=reboot -F=force-startup-checks -k=just-send-warning . Time is "now" or "+N" in N minutes or absolute time e.g. 23:58.
 ==== 102 Installation and Package Management 18% ====
@@ Line 40: / Line 92: @@
   * Knowledge of basic features of LVM
   * Terms: / (root) filesystem, /var filesystem, /home filesystem, swap space, mount points, partitions
+==Notes==
+  * choosing a disk layout for linux depends on amount of disk space, purpose of the system, size of the system and backup strategy. Some general guidelines are
+    * If diskspace is limited, just /boot, / and /swap
+    * /boot is a separate 50MB partition because older kernels/BIOS require kernels under a 1024 cylinder limit.
+    * For larger systems keep / smaller/simpler to reduce risk of corruption.
+    * Can use separate partitions for /var (to isolate system logs), /tmp (to isolate tempfiles), /home (for backup and RAIDing of user's data)
+    * Using a separate partition for /usr allows it to be shared via read-only NFS which allows for saving space and easier maintenance of apps/updates.
+  * Superblock on filesystem contains critical metadata so multiple redundant copies are kept.
+  * Filesystems must be mounted (listed in filesystem table) before being accessible. /etc/fstab is a list of filesystems to mount on boot up.
+  * Master Boot Record on first 512 bytes of first sector of disk contains info on partitions and bootup. Can be backed up and restored with <code>
+dd if=/dev/hda of=~/mbr.txt count=1 bs=512
+dd if=~/mbr.txt of=/dev/hda count=1 bs=512
+</code>
+  * To backup/restore just the partition layout, use sfdisk <code>
+sfdisk -d /dev/hda > partition_backup.txt
+sfdisk /dev/hda < partition_backup.txt
+</code>
+  * Linux may also be booted from Live USB which allows for persistent modifications. If the BIOS does nto support this, a bootable CD can be used first.
+  * Swap space allows main memory to be temporarily copied to disk. As a starting point set swap to twice the memory size (at least the same size).
 === 102.2 Install a boot manager (LCN-5 CTL-5) ===
@@ Line 47: / Line 120: @@
   * Interact with the boot loader
   * Terms: /boot/grub/menu.lst, grub.cfg and other variations, grub-install, MBR, superblock
+==Notes==
+  * BIOS looks for and runs boot loader from first specified boot device.
+  * Boot loader find and loads specified kernel (with specified kernel options) which loads required modules and starts system processes.
+  * LILO is a 2-stage program
+    * First stage is in 512-byte MBR or in the boot sector of a partition (if it is a secondary boot loader).
+    * Second stage is in /boot/boot.b .
+    * Map file locating kernel is in /boot/map
+    * //lilo// command reads /etc/lilo.conf which contains kernel image locations, kernel options, the default boot disk etc. It encodes this information along with physical disk information and writes it into the boot files (MBR/boot-sector, boot.b and map).
+  * GRUB is a multi-stage boot loader, more flexible than LILO.
+    * Changes take effect immediately.
+    * (hd0,1) -> 2nd partition on the 1st hard disk. Refers only to the order of the disks as seen by the BIOS so order may change if BIOS boot order is changed.
+    * //grub-install// writes to MBR/boot sector. Uses/boot/grub/device.map to map BIOS drives to Linux devices e.g. "(hd0)   /dev/sda".
+    * Grub command-line expects a specific order of commands to boot kernel <code>grub> root (hd0,0)
+grub> kernel /vmlinuz-2.4.18-14 ro root=/dev/hda2
+grub> initrd /initrd-2.4.18-14.img  [optional]
+grub> boot</code>
 === 102.3 Manage shared libraries (LCN-5 CTL-2) ===
@@ Line 65: / Line 156: @@
   * Determine what files a package provides, as well as find which package a specific file comes from
   * Terms: rpm, rpm2cpio, /etc/yum.conf, /etc/yum.repos.d/, yum, yumdownloader
 ==== 103 GNU / Unix Commands 43%   ====