Os Test 1 Material

Front 1

fork

Back 1

A system call th­­at creates a new process by creating a logical copy of the current process. Each copy has a return value the child is 0, the parent is the childs PID.

Front 2

kernel

Back 2

The part of the operating system that runs in supervisor mode on the CPU and has the code that is run for all interrupts. First thing that loads after boot. Determines how everything else runs by allocating memory for each process which is called virtualization.

Front 3

file

Back 3

A stream of bytes associated with a hierarchical name. Stored in kernel, location is stored in inode numbers.

Front 4

system calls

Back 4

The API used by a process to access outside resources (disk/user input/network) that are inside the kernel.

Front 5

shell variables

Back 5

A variable that can only be accessed within the current shell.

Front 6

environment variables

Back 6

Process specific. A variable that can be accessed within the current process and in child processes (unless filtered).

Front 7

zombie process

Back 7

A process that has terminated but its parent has not retrieved its return value.

Front 8

library

Back 8

An indexed collection of object files that may be linked into a program. Contains a bunch of functions that may be needed for reuse. Ex. C std lib

Front 9

execve

Back 9

A system call that loads an executable into the current process and runs it (erasing the process's old code and data).

Front 10

thread

Back 10

A schedulable entity with its own CPU context that can share its memory with other schedulable entities.

Front 11

signals

Back 11

A type of inter-process communication that is also used in UNIX to manage processes. The signal is sent through the kernel to get to the other process. Interrupt signal, kill signal... when the

Front 12

function call

Back 12

Compile time, calling a function. (An invocation of code present inside of a process that was included when the program was compiled.)

Front 13

library call

Back 13

Run time, calling a function that we have to get dynamically from a library by going outside of the program. (An invocation of code present inside of a process that was loaded into the process at runtime. A function used that came from a library.)

Front 14

process

Back 14

a running program that thinks it has its own cpu. It has it's own memory location and it's own register state. (The main abstraction for running programs that gives each program its own memory and virtual CPU.)

Front 15

filesystem

Back 15

A hierarchical collection of key/value pairs, where the values are inodes - that point to the metadata - which helps locate the file - which is a streams of bytes of arbitrary length. The key is the file name.

Front 16

init

Back 16

The booting component that takes parts of the kernel and puts them where they belong its a setup. it runs on a UNIX-like system.

Front 17

wait

Back 17

It is called by a parent when the child has terminated to receive the return value (PID) to free the process resources like memory. ( A system call to get the return value of a process that has terminated.)

Front 18

disk

Back 18

a device for storing data. Example of a block device because it stores data in blocks.

Front 19

device driver

Back 19

The computer that's in the device that provides an API on how to actually use the device. (Code that runs in the kernel and abstracts access to a specific piece of hardware.)

Front 20

kernel module

Back 20

Attachment to the kernel that modifies it - the project we have to do is create one - can be loaded and unloaded, easy to use which is why they've been made. (Code that is loaded into to the kernel at runtime in order to add (or change) kernel functionality)

Front 21

fsck

Back 21

If files may have been corrupted, you can go here to check, and also retrieve other informations - check/repair.

Front 22

root filesystem

Back 22

The home directory of a filesystem that all of the other filesystems spawn from ( A set of files and directories that must exist on every UNIX system. )

Front 23

make

Back 23

A program that directs the compilation of other programs.

Front 24

block device

Back 24

buffered IO device that stores information/data. A UNIX device abstraction that is primarily used for persistent storage devices. Not the hard drive itself but the information the hard drive needs to store in a buffered block.

Front 25

character device

Back 25

Non buffered/stored data. A UNIX device abstraction that allows byte-level access to hardware (input and/or output). It is often used today to represent keyboards, mice, and printers.

Front 26

root user

Back 26

The user account on a UNIX system with the highest level of privileges.

Front 27

superblock

Back 27

The inode of the filesystem. The block that stores metadata about a filesystem needed to properly mount it.

Front 28

inode

Back 28

Metadata about a file. Contains location in memory(to allow access), size etc. Defines the structure of the file where as the data defines what is put into the structure. (An on-disk data structure that stores file metadata including length, modification times, and ownership information.)

Front 29

extents

Back 29

Sequential ranges of blocks used to store file data.

Front 30

logical size of a file

Back 30

The size of a file as seen by a program accessing that file. Actual file size in bytes. (Note: Physical size is the size of the total number of blocks needed to store it. )

Front 31

kernel oops

Back 31

Null exception error in the kernel space. Happens when the kernel detects an internal error, such as access to an illegal memory location, that can generally be recovered from. It produces a certain error log.

Front 32

pseudo tty

Back 32

Teletype interface, way of communicating with the terminal like a virtual keyboard. Like a terminal, means to send input to the computer (A UNIX device that virtualizes keyboard input and text output.)

Front 33

/proc

Back 33

A virtual filesystem (into ram instead of in persistent storage) that allows access to kernel state in mostly human-readable formats.

Front 34

/sys

Back 34

A virtual filesystem that allows access to kernel state where every file stores exactly one value.

Front 35

mount

Back 35

Command to make thecontents of a filesystem accessible.

Front 36

rmmod

Back 36

Command that unloads a module from the currently running kernel.

Front 37

ls -lt | head

Back 37

a command that lists the recently modified files in a directory.

Front 38

lsmod

Back 38

a command for listing the modules loaded into the kernel

Front 39

/dev

Back 39

The part of the filesystem normally used to give names to connected hardware. Provides interfaces that are the names so you can access them, the device drivers might live in here.

Front 40

what can the kernel do that regular processes cant?

Back 40

Make syscalls, access kernel space, use reserved hardware resources, schedule the CPU.

Front 41

why wouldn't you want to do things inside the kernel

Back 41

Because it can get complicated and risky. A bunk program can peace out but a bunk kernel module could mess it up.

Front 42

device files

Back 42

dd is used to make this interface for device drivers. Only used for peripherals. Block and character devices are examples.

Front 43

how does mounting change the filesystem hierarchy?

Back 43

when you mount a filesystem you're expanding the root filesystem.

Front 44

where are permissions stored?

Back 44

the inode because it has all of the metadata.

Front 45

why cant you make a system call using a function call mechanism

Back 45

someone email anil about this or post on the forum lol.

Front 46

how do you create and destroy a process?

Back 46

create: run a program - fork, execve
destroy: kill -9

Front 47

how to create and destroy processes

Back 47

The Process API – what must be included in any interface of an operating system:Create: method to create new processes, when you type a cmd into the shell or click on an icon, the os is invoked to creake a new process to run the program you have indicated.Destroy: systems provide an interface to destroy processes forcefully. Many processes will run and exit when complete;but when they don’t the user can kill them; making a interface to halt a process useful.Wait: sometimes useful towait for a process to stop running.Miscellaneous Control: anything other than basics. Ex: most operating systems provide some method to suspend a process then resume it.Status: interface to get some status information about a process. Ex: runtime, state.

Front 48

Process States: at a given time a process can be in one of the following three states

Back 48

Running: a process is running on a processor and executing instructions.Ready: a process is ready to run but the OS has not chosen to run it yet at the moment.Blocked: a process has performed some operation that makes it not ready to run until another event takes place like maybe an I/O request on a disk blocks the process so another process uses the processor.

Front 49

strace

Back 49

system call tracer

Front 50

ltrace

Back 50

library call tracer

Front 51

how do you load program binaries?

Back 51

compile it first.

Front 52

how are libraries incorporated into programs?

Back 52

statically linked or dynamically linked.

Front 53

Statically Linked

Back 53

at compile time. Statically compiled programs are much larger in size.

Front 54

Dynamically linked

Back 54

at runtime.

Front 55

how are processes controlled using signals, command line variables, and environment variables?

Back 55

Signals can tell the process what to do. Cmd line variables
Environment variables