Linux Flashcards
What are the characteristics of linux
Flexibility, Multitasking, Multi-user, Portable
USER <-> SHELL <-> kernal <-> Hardware
Functions of a shell
Acts as command interpreter, performs I/O, manages environment.
Functions of a kernal
Manages creation and termination of processes. Manages allocation of memory. manages filesystem. Manages system I/O
BIOS tasks
-performs POST
-hardware setup and config
-boot device is selected and loaded
Grub stage 1 tasks
-Small machine code located in MBR
-Sole purpose is to locate and load second stage of boot loader into memory
GRUB stage 2 tasks
-kernal selection menu is displayed
-Loads initial RAM into memory, known as initrd
-Loads kernal into memory
Linux Kernal
-Initializes and configures memory and hardware
mounts initrd to load drivers.
-Mounts file root system
-Executes /sbin/init
BIOS -> GRUB1 -> GRUB2 -> kernal
What are the 3 kinds of linux drivers
Module, loadable kernal module, Device Drivers
What does the module driver do
A piece of code that can be added to kernal at runtime
what does the Loadable kernal module (LKM) do
Adds and removes functionality to the kernal while system is running
what do device drivers do
Allows system to communicate with the system hardware and peripheral devices
What is virtualization
Process of creating software-based version of something
host OS
OS running virtual environment can run several guest OS
Guest OS
OS inside virtual environment
Hypervisor
Seperates OS from hardware; AKA abstraction layer
Logical resources
Representation of physical resources
Physical resources
actual underlying hardware (RAM, CPU)
What is server virtualization
One physical machine divided into many virtual servers.
Utilizes hypervisor
What is application virtualization
-Java/python VMs
-Streaming applications from a central location
What is network virtualization
Combination of multiple networks (VPNs)
-Logically seperate physcial network with virtual network devices
What is containerization
-Contains everything to run a piece of software
-Shares the kernal with other containers
Advantages of virtualization
-Consolidation of hardware resources
-Multiple instances of OSs can run on one machine
Advanced RISC machine (ARM) processor
-Majority of phones use the arm process
-ARM uses the reduced instruction set computing (RISC)
Three key attributes of ARM processors
Small implementation size, good performance, very low power consumption
ARM Instruction set
set of 32-bit instructions
provides comprehensive data-processing and control functions
THUMB instruction set
-set of 16-bit instructions
-Provides significantly improved code density, at cost of reduction in performance
What are the 5 layers of android
Linux kernal, Libraries, Android runtime, Application framework, Applications
what is Linux kernal (layers of android)
-Lowest level, built on linux kernal
What are libraries (layers of android)
Provides native libraries, low level functionality
What is android runtime (layers of android)
Dalvik VM, core android library
What is application framework (layers of android)
-Java libraries to build applications
What are applications (layers of android)
All the applications on the system
What is the boot process of an android OS
1) Boot ROM 2)Boot loader phase 1 3) Boot loader phase 2 4) kernal phase 5) init 6) zygote 7) system servers 8) system servers 9) Home applications 10) contacts
What does the boot ROM phase do
-Performs check of all chip components
-Detects boot media and locates first stage of boot loader
-loads boot loader first stage into RAM
What does boot loader stage 1 do
Boot loader detects and sets up external RAM
Loads boot loader stage 2 into external RAM
What does boot loader stage 2 do
-Sets up hardware such as networking and additional networking
-Looks for linux kernal and loads it into memory
-Passes control to kernal
What does the kernal stage do
Setup memory protection, caches, and scheduling
starts init process
What does the init stage do
-Starts each system service daemon in separate processes
-Starts zygote process
-Starts runtime process
What does the zygote stage do
Runtime process tells zygote to start system server
Listens for requests to spawn Dalvik VM instances
What does the system server stage do
-Starts native system servers and android managed servers
What does the home application stage do
Idle screen, zygote loads home application in new Dalvik VM
What does the contacts stage do
Zygote loads contacts process in new Dalvik Vm
command = ln
makes links between files. -s is symbolic
command = chmod
Changes permissions on file
command = chown
-Changes ownership [owner][:group]
suid bit
-Allows executable to run with permissions of the file owner
sgid bit
Allows executable to run with permissions of the group
subfolders retain sgid bit
command = whatis
displays one line manual page description
command = which
prints full path of executable.
command = whereis
Locates binary path for a command
command = hostname
shows system hostname
command = uname
-prints certain system info, such as kernal name, release version
shell variables
Variables contained exclusively in shell which were set
packages
A consolidation of files needed to provide a feature to the OS, such as a text editor
Repository
Central location where packages are stored
command = tr
performs substitution or deletion of selected characters
/proc/pid
Files that provide information about the process
systemctl
control systemd system and service manager
NFS
-Internet standard protocol for file sharing between systems
command = ifconfig
used to configure network interface
command = route
manipulates kernal IP routing table
command = ssh
Logging into a remote machine
command = iptables
edit tables to store set of firewall rules
admin table for ipv4 packet filtering and NAT
regular expressions
sequence of characters that define a search pattern for text
/var/log
Holds most system log. only accessible by root
/var/log/secure
contains info related to authentication and authorization priveledges
/var/log/lastlog
contains info on last login. viewed using lastlog
var/log/btmp
contains info on failed logins. viewed by lastb
var/run/utmp
contains info on who is currently logged in. Viewed by who command
/var/log/wtmp
Contains all logins/logouts. viewed by last
auditctl
used to configure options related to auditing
