Linux Command Line Commands

Front 1

WHAT IS THE COMMAND LINE INTERFACE CALLED?

Back 1

THE SHELL

Front 2

What is the proper syntax for a Linux command?

Back 2

{ProgramName} {'-'Option} {Argument}

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cd

Back 3

CHANGE DIRECTORY

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cd ~

Back 4

CHANGE DIRECTORY BACK TO HOME DIRECTORY

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cd -

Back 5

CHANGES DIRECTORY TO THE PREVIOUS DIRECTORY

Front 6

cd ..

Back 6

GO UP 1 DIRECTORY LEVEL

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ls

Back 7

List the contents of a directory

Front 8

mkdir

Back 8

MAKE DIRECTORY

Front 9

pwd

Back 9

PRINT

WORKING

DIRECTORY

Displays current working directory

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ls

Back 10

LIST CONTENTS OF DIRECTORY

Front 11

rm -rf {DIRECTORY}

Back 11

REMOVES THE DIRECTORY AND ALL FILES AND DIRECTORIES WITHIN (USE WITH CAUTION!)

-r = recursively

-f = force eg. never prompt & ignore any non-existent files & arguments

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commonly used ls options

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-a : List all files, incl. hidden ones

-color : List files with colorized output

-d : List directory names and not their contents

-l : Long format

-r : List in reverse order

-R : List files recursively

-t : sort by time, most recently modified first

-S : list files by size

-s : list files and show sizes

-n : shows file contents with line numbers

head -n(# of lines) : shows a specific # of lines

Front 13

mkdir

Back 13

MAKE DIRECTORY

mkdir -p = make directory with full path, which means create the directory and any sub-directories listed

Front 14

Command-line is more efficient than GUI. Why?

Back 14

FASTEST, MOST FLEXIBLE AND SOMETIMES THE ONLY WAY TO ACHIEVE A DESIRED OUTCOME

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cp

Back 15

COPY FILE

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cd

Back 16

CHANGE DIRECTORY

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rmdir

Back 17

REMOVE DIRECTORY

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rm

Back 18

REMOVE

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".."

Back 19

THE ".." CHARACTERS REFER TO THE PARENT OF THE CURRENT WORKING DIRECTORY

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tail

Back 20

SHOWS LAST TEN LINES (OR HOWEVER MANY LINES SPECIFIED IN SYNTAX)

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mv

Back 21

MOVE FILE (OR DIRECTORY?)

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head

Back 22

SHOWS FIRST TEN LINES (OR HOWEVER MANY LINES SPECIFIED IN SYNTAX)

Front 23

What are the benefits of using a virtual machine?

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1) EASY AND INEXPENSIVE OR

ICAL MACHINE

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>

Back 24

REDIRECTS AND OVERWRITES THE OUTPUT (FROM A COMMAND SUCH AS LS, CAT, CP OR MV)

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touch

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CREATE A NEW & EMPTY FILE

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Control + d

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EXIT ENTERING TEXT LINES IN A FILE

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What is "cat" short for?

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CONCATENATE meaning "to link together"

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>>

Back 28

REDIRECTS THE OUTPUT AND APPENDS THE FILE

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"."

Back 29

"." REFERS TO THE CURRENT WORKING DIRECTORY

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cat (to display the contents of a file)

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To display MyShoppingList.txt in the directory home/joe to the terminal window screen

$ cat MyShoppingList.txt

(Press "q" to quit)

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cat (to write text to a file)

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WRITE/SHOW CONTENTS OF A FILE. WITH ARGUMENTS CAN COMBINE FILE DATA

i.e.

$ touch MyShoppingList.txt

$ cat > MyShoppingList.txt

My List:

Cheese

Bread

Milk

ctrl + d to end entering text

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tee

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Allows for redirecting stdin to stdout i.e. ls | tee parts.txt will show the results of ls on the std output AND in parts.txt.

Use -a option to append to the file output instead of overwriting or creating a new file.

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cd /

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CHANGE DIRECTORY TO ROOT DIRECTORY

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"~"

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"~" REFERS TO THE USER'S HOME DIRECTORY

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man -k {KEYWORD}

Back 35

SEARCH POSSIBLE COMMANDS THAT RELATE TO THAT KEYWORD

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Using "cat" with the more command

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Display the contents of a large file one screen at a time i.e.users/sysadmin: $ MyShoppinglist.txt |less

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clear

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CLEARS THE SCREEN

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man {COMMAND}

Back 38

SHOWS THE MANUAL FOR A GIVEN COMMAND

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which {command}

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TO FIND OUT EXACTLY WHERE A COMMAND IS LOCATED

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$PATH

Back 40

DETERMINES THE VALUE OF PATH (ie. WHAT DIRECTORIES CONTAIN EXECUTABLE COMMANDS AND IN WHAT ORDER THEY ARE SEARCHED)

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Using "cat" with the less command

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Display the contents of a large file all at once so you can scroll up and down a file

i.e.users/sysadmin: $ MyShoppinglist.txt |more

(Press "q" to quit)

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echo

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DISPLAYS A VALUE ON YOUR OUTPUT (SUCH AS YOUR SCREEN OR A DOCUMENT)

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tree -c

Back 43

colorize the output

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wc

Back 44

WORD COUNT

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tree

Back 45

LIST THE CONTENTS OF A DIRECTORY IN TREE FORMAT

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wc -l {filename}

Back 46

Counts the lines of code in a file

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tree -d

Back 47

list directories only

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sudo

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RUN AS SUPERUSER/ADMINISTRATOR/ROOT

Stands for 'super user do'

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eog {filename}

Back 49

Eye

Of

Gnome

VIEW IMAGE FILE FROM WITHIN TERMINAL

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grep

Back 50

SEARCH FOR DATA WITHIN GIVEN FILES

Syntax: grep -i or -il (search term) (file name or *)

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grep -i

Back 51

SEARCH FILES WITHOUT CASE SENSITIVITY

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grep -il

Back 52

SEARCH FILES WITHOUT CASE SENSITIVITY AND SHOW ONLY FILE NAMES

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grep -ri

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SEARCH FILES RECURSIVELY (THROUGH SUBDIRECTORIES)

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find

Back 54

FIND FILES AND DIRECTORIES, DEPENDING ON WHAT PARAMETER YOU PLACE NEXT TO THE FIND COMMAND

ie find -f : finds files

find -d : finds directories

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Linux file system structure

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/ = root

/home = home dir contains user private files

/etc = config files

/bin, /sbin = binaries; contains applications

/ var = contains files that change over time

/tmp = contains temp files

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ll

Back 56

= ls -l : shows the permissions of a given file or folder

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ls -l (file/folder)

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Shows permissions of a given file or folder

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ps aux

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Shows a snapshot of all commands running at time of snapshot

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PS aux | grep -I "(process)"

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Snapshot of all processes grep'd into a search of specific process

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top u + username you wish to check

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Shows processes running under that username

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kill

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Used to kill processes

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kill -9 (process #)

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Kill a process

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sudo killall (app/process ie. Firefox)

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Kill all processes associated with a specific application

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tar

Back 64

STANDS FOR "TAPE ARCHIVE"

The way to create backups or archives of specific files or folders.

Syntax example:

sudo tar cvvWf 20200829_backup.tar

/var/log

Will create a full backup of the /var/log directory.

sudo tar cvvWf 20200829_backup.tar /var/log [> or >>] /var/log/backups_log_file.txt

Will create a full backup of the /var/log directory and redirect the output to a log file called backups_log_file.txt

Syntax breakdown:

sudo tar cvvWf [archive_name] [objects_to_archive

sudo ]

sudo = because /var/log contains system files therefore u need 'root' privileges to access them.

tar = the command

cvvWf = short form options:

c = create

vv = very verbose. It will display

the file name & path & the

permissions, owner, group,

size, creation date, and time

of each file as it is added to

the archive

W = verify

f = use this archive file, followed

by the name of the archive

20200829_backup.tar is the archive name.

/var/log = the objects (files or directories) to archive

Front 65

Using tar to create incremental backups

Back 65

Syntax: sudo tar cvvWf (archive_name).tar --listed-incremental=(snapshot_name).snar --level=0 /var/log

will create a full backup of the /var/log folder

and

sudo tar cvvWf (archive:_name).tar --listed-incremental=(snapshot_name).snar /var/log

will create an incremental backup of the /var/log directory

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Creating full backups using tar command

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Syntax: tar cvvWf (archive name).tar (directory_name)

ie. tar cvvWf tape_backup_20200827.tar ~/Documents/Downloads/

will create a full backup of the ~/Documents/Downloads directory.

Front 67

Checking the contents of a tar file (same goes for compressed files)

Back 67

SYNTAX: tar tvvf (tar_file).tar | less

Syntax breakdown:

tar = the command

tvvf = options

t = list the contents of an archive

vv = very verbose. Lists all relevant file information

f = stands for this file

[tar_file.tar] = archive name

| less = pipes the output to less so that we can scroll thru the data

Front 68

tar best practices

Back 68

•Make sure that archives are not writable by an untrusted user

• Sanitize data, such as passwords, before writing to an archive

• Monitor all backups, as tar is vulnerable to DoS attacks

• Pay attention to the diagnostic and exit status of tar

Front 69

Extracting block of data from an archived file using tar command into a specified directory

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1st step : mkdir restored_emails

Syntax :

tar xvvf 20190510_backup.tar -R -C restored_emails --wildcards "*.csv"

Syntax breakdown:

tar = command

xvvf = options

x = extract data

vv = very verbose

f = this archive file

20190510_backup.tar = the archive file

-R = print error msgs for any error with the block number in the archive file when extracting files

-C = what directory you want to save the untarred files

restored_emails = the directory where you want to save the extracted/untarred files

--wildcards "*.csv"= extract a group of files whose pattern begins with .csv

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Extracting files into current directory using tar

Back 70

Syntax:

tar xvvf -R file_backup.tar

Syntax breakdown :

tar = the command

xvvf = options

x = extract

vv = very verbose

f = this archive file

file_backup.tar = the archive file

Front 71

Create a tar archive with compression using gzip and bz2

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Syntax 1:

tar cvvzf 20200829_backup.tgz /home/Images

Syntax breakdown :

tar = the command

cvvzWf = options

c = create

vv = very verbose

z = compress archive using gzip

f = this archive file

20200829_backup.tgz = the archive file

/home/Images = the directory to be archived

Syntax 2:

tar cvvjf 20200829_backup.bz2 (or .tbz or .tb2) /home/Images

Syntax breakdown :

tar = the command

cvvjf = options

c = create

vv = very verbose

j = compress archive using bz2 (higher compression but slower compression rate)

f = this archive file20200829_backup.bz2 = the archive file

/home/Images = the directory to be archived

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Untar /unzip compressed archive file

Back 72

Syntax 1:

tar -xvvf 20200829_backup.tgz Syntax breakdown :

tar = the command

cvvzf = options x = extract vv = very verbose z = compress using gzip f = this archive file20200829_backup.tgz = the archive file

Syntax 2:tar -xvvf 20200829_backup.bz2

Syntax breakdown :tar = the commandcvvzWf = options x = extract vv = very verbose f = this archive file20200829_backup.bz2 = the archive

Front 73

Untar a single file from a tar archive

Back 73

Syntax:

tar -xvvf 20200829_backup.tar image_1.jpg

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Untar multiple files, sequential, from a tar archive (same goes for compressed tar archives)

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Syntax:

tar -xvvf 20200829_backup.tar "image_{1-25}.jpg

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Untar multiple files, non-sequential, from a tar archive (same goes for compressed tar archives)

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Syntax:tar -xvvf 20200829_backup.tar "image_1.jpg" "image_24.jpg"

tar -zxvvf 20200829_backup.tgz "image_1.jpg" "image_24.jpg"

tar -jxvvf 20200829_backup.bz2 "image_1.jpg" "image_24.jpg"

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Add files or directories to a tar archive file (cannot do this with compressed archives)

Back 76

Syntax:

For a file:

tar -rvvf 20200829_backup.tar image_1.jpg

For a directory:

tar -rvvf 20200829_backup.tar php

Front 77

From where did cron get its name?

Back 77

Kronos, Greek God of Time

Front 78

cron tasks are scheduled in....

Back 78

A file called crontab (short for CRON TABle)

Front 79

What is the command to create or edit a cron file?

Back 79

crontab -e

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How can you tell if a service is running?

Back 80

systemctl status [service_name]

Front 81

How to tell if the cron service is up and running?

Back 81

systemctl status cron

Front 82

Command to list the contents of a crontab?

Back 82

crontab -l

Front 83

What is the basic syntax for a command within a crontab?

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min hr date month weekday command

min = 0-59

hr = 0-23

date = 1-31

month = 1-12

weekday = 0-7 (0 & 7 = Sunday)

* = every ie. * in any value means every one of that value

Example:

If you want to delete everything in your Downloads folder every Saturday at 11 pm:

0 23 * * 6 rm ~/Downloads/*

Front 84

how to use conditional statements in awk

Back 84

awk '{if ($# >= 1000) print $0}'

Front 85

What does < echo $? > do?

Back 85

It is a special variable that will display the exit status of the previous command. An exit code of 0 indicates that the previous command ran successfully. Anything greater indicates an error.

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What does 2>&1 mean vs 2>/dev/null?

Back 86

2 = stderr

1 = stdout

/dev/null = a UNIX device file that discards all data written to it and yeilds no output

>& = redirect file descriptor

Therefore 2>&1 means if an error occurs, redirect the stderr to the stdout. 2>/dev/null means if an error occurs, redirect the stderr to /dev/null which will write the error and show no output. (You can echo $? to see if an error occurred)

Front 87

Logrotate: What is the command syntax tk restart logrotate using the new/edited config file?

Back 87

sudo logrotate -vf /etc/logrotate.conf

Front 88

What does TTP stand for?

Back 88

Tactics

Techniques

&

Procedures

Front 89

For Loop

Back 89

Syntax:

Numerical looping -

for ((i=0; i < 1000; i++))

do

echo $i

done

Iterating over a list -

for VAL in 20 3 dog 7

do

echo $VAL

done

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If statements, command conditional

Back 90

if cmd

then

some cmds

else

other cmds

fi

Front 91

If statements, file & numerical conditionals

Back 91

if [[ -e $FILENAME ]]

then

echo $FILENAME exists

fi

File Test =

-d = directory exists

-e = file exists

-r = file is readable

-w = file is writable

-x = file is executable