INFX 450 Exam 2

vi

default editor in all linux systems

ps (process status)

displays a snapshot of processes currently running. non-interactive

Jobs command

displays active jobs and identifies if foreground, background, or stopped. allows the user to directly interact with processes in the current shell.

ps -e

displays every active process( all users logged in)

summary of disk usage

du -s

top

dynamically displays running processes; interactive display process statistics continuously until stopped.

\

escape sequence that tells the interpreter not to interpret the following character, but rather use it as a literal. Ex. if you want to search for a "." use "\." so egrep \. filename

list of empty files

find ~ -empty

SIGHUP (kill signal 1)

hang-up; terminates communication if a signal is lost; restarts the process with the exact same PID

if then else statement

if something is true -> do it, or if the next something is true -> do it, ... if now of the above are true, do else

if then statement

if something is true do it, otherwise execute the then portion

{}

indicates number of times to match the preceding character

ppid

parent process ID

foreground process

A process for which the BASH shell that executed it must wait for its termination.

background process

A process that runs "behind the scenes" with a low priority, does not require input, and rarely creates output. (11)

Child Process

A process that was started by another process (parent process).

Fork() system call

Creates a new process

VariableName=Value

Creating and assigning a value to a variable

slide 12 Ch. 7 Part 2

Different echo options for input and output

-20

Highest priority level

& <- added to the end of the command

How to launch a background process?

nice -n 12 my-job

Launch my-job setting the nice value to 12

-20 to +19

Niceness value is an integer that ranges from

niceness value high nice value = lower priority

Priority is established by setting the

foreground or background

Process can run in either?

date

Shows the date in bash

Systemd

The first process that spawns at the system boot; is the parent of all processes. First to start and runs until system shuts.

Parent Process

The original process that initiates and controls execution of a child process.

fg job_ID, fg is for stopped jobs

To move a background process to the foreground.

bg

To move a foreground process to the background

bg #

To resume the process in the background.

fg #

To resume the process in the foreground.

Ctrl-Z

To suspend a process in the foreground

$! /bin/bash date du -s ~ find ~ -empty

Write a script to run a simple status report: show the date, summary of disk usage, and a list of empty files

Process

a running program; any program that is executing on your system

regular expression (regex)

a special text string for describing a search pattern. used for searching, text processing, and data validation. used to identify and manipulate specific pieces of data.

variable

a symbolic name for a memory location that we can assign values, read the data, and manipulate its contents.

-Power- options can usually be implemented through the GUI, but it takes more resources, time, and operactions -sometimes you dont have access to the GUI, if youre remotely logged in, GUI has failed, have a need for a minimal installation

advantages of using a text line editor:

vi mode (command mode)

all keys pressed by the user are interpreted as commands press ESC to enter command mode

loops

allow you to execute commands repetitively

text editors

allows you to edit text files from GUI text editor or a command line text editor.

interpreter

bash is an

shutdown commands

brings the system down in a secure way. when used all logged in users and processer are notified that the system is going down, and no further logins are allowed.

SIGKILL (kill signal 9)

brute-force kill; if th e process was hung badly, this option will force it to stop; Linus immediately kills with no chance for process to clean up

command

command name

pcpu

cpu utilization

?

preceding character can appear 0 or 1 times exactly

*

preceding character can appear 0 or more times

+

preceding character can appear 1 or more times

pid

process ID

User processes

process created by the user when he/she enters a command at the prompt

stat

process status

if condiftion

returns two values and returns true or false

ps -aux

same as ps -e just displays a different format. a: all processes running u: user oriented format x: list all processes not attached to a terminal

#! /bin/bash echo Hello $USER. Here are the running processes. ps

script that greets the user and shows the running process list

#! /bin/bash ls -l | grep '^d'

script that uses "ls" to display only directories

Finding files and directory's through script

slide 22 Ch. 7 part 2

if statement

something is true then do x

metacharacters (regex)

special characters that are applied to a specific literal character and change the rules for matching that literal character Ex. ". * +"

literal characters (regex)

specific characters that must match precisely, in the order given, and with correct case. Ex. "ca" matches car and can

SIGTERM (kill signal 15)

tells process to terminate immediately; default signal sent by kill; allows process to clean up after itself before exiting.

find ~ -empty >> empty.txt

the empty files are written to the text file empty.txt

vi mode (replace mode)

this mode isfor typing text in an over write mode press "R" to enter this mode

"if" statements

to make a decision in your script us

vi filename

to open a new text file on vi with a specific file name

read

to read input from the keyboard; reads data until you press the enter key Ex. read X Y Z user would input 2 4 6 and these numbers would be assigned

Case statement

used for comparisons similar to multi-level if then else statements matches a variable against several values

[]

used to specify a list of choices; ,atch any one single charcter in the list

user

username

ps -al

view all process with the long format

"$"

when you want to view the contents of a variable

read -p "Enter 5 integer values: " one two three.. let result="($one + $two + $three + $four + $five)/5" echo "the average is $result"

write a script that prompts the user to input 5 values and output the average of the 5 values

#! /bin/bash hostname arch who

write a script that provides some basic system information (hostname, CPU info, Who is logged in)

./SysTest.sh >> output.txt

write the output of the entire script to a text file using redirection

To do math in bash

you must denote the values in variable are to be interpreted as numbers and not strings. to do so precede assignment statement with "let" Ex. let a=n+1

i (insert)

mode to enter text

nice

niceness value

To create a script

1. Create script file in a text editor; First line is #! /bin/bash 2. Change permissions with chmod to make the file executable use "chmod 745" 3. Run script using ./filename

shell script

is a series of commands written in a file. used for repetitive tasks, shortcuts for convoluted commands, easy to use command line interface.

TTY

is the controlling terminal associated with the process, run this to see the terminal name

grep (Global Regular Expression Print)

is used to search text. It searches the given file for lines containing a match to the given strings or words.

kill

kill a process by PID

killall

kill a process by name

egrep

lets you search with the extended metacharacters.

+19

lowest priority level

. (metacharacter)

matches any character (except line breaks) Ex. "b.t" matches bit and but, DOES not match boot or b123t

$

matches end of line

^

matches start of line

vi mode (Input mode)

mode is for inserting new text and editing/replacing existing text press "i" to enter mode