Linux essentials

Question 1

tar -tvf

Answer 1

t = list v = verbose, f=filename

Question 2

tar -z

Answer 2

compressed file with gzip

Question 3

tar -c

Answer 3

create a tar file

Question 4

ls -l

Answer 4

list files long (extra info

Question 5

ls -h

Answer 5

list files, human readable

Question 6

tar -xvf

Answer 6

extract files, verbose, file name

Question 7

tar -r

Answer 7

add to existing archive

Question 8

cp

Answer 8

copy

Question 9

gzip

Answer 9

zips file, replaces old one

Question 10

gzip -r

Answer 10

-r is recursive (subdirectories)

Question 11

tar -j

Answer 11

compresses with bzip2

Question 12

tar -t

Answer 12

list contents of the archive

Question 13

tar -z

Answer 13

compresses with zip

Question 14

stderr

Answer 14

Standard error (stderr) occurs when an error appears during the execution of a command; it has a file descriptor of 2. Error messages are also sent to the terminal window by default.

Question 15

stdin

Answer 15

Standard input, stdin, usually is provided by you to a command by typing on the keyboard; it has a file descriptor of 0. However, by redirecting standard input, files can also be used as stdin.

Question 16

stdout

Answer 16

stdout. The file descriptor number for this channel is 1.

Question 17

tr

Answer 17

the tr command translates characters, but it only accepts data from stdin, never from a file name given as an argument. This is great when you want to do something like capitalize data that is inputted from the keyboard

Question 18

more

Answer 18

pipeable/redirect command to do more of a long command

Question 19

cut

Answer 19

The cut command is useful for extracting fields from files that are either delimited by a character, like the colon : in /etc/passwd, or that have a fixed width

Question 20

head

Answer 20

top 10 lines of a file/dir

Question 21

tail

Answer 21

last 10 lines of a file/dir

Question 22

head -2

Answer 22

first two lines of that dir

Question 23

head -n -#

Answer 23

head command is to use the option -n -#, where # is the number of lines counted from the bottom of the output to exclude. Notice the minus symbol - in front of the #

Question 24

grep -e

Answer 24

The -E option to the grep command can be used to perform searches with extended regular expressions, essentially more powerful regular expressions. Another way to use extended regular expressions is to use the egrep command.

Question 25

fgrep

Answer 25

The fgrep command is used to match literal characters, ignoring the special meaning of regular expression characters.

Question 26

grep '^###'

Answer 26

Only files with beginning in ### will show

Question 27

grep '###'

Answer 27

Searches for ### anywhere in a line

Question 28

grep ###

Answer 28

Greedy, matches with anything with ### in it

Question 29

grep '###$'

Answer 29

searches for ### at the end of a line

Question 30

grep '.y'

Answer 30

Use the period character . to match any single character. For example, execute the following command to match any character followed by a 'y'

Question 31

egrep ###|###

Answer 31

the | in egrep acts as an "or" statement | in egrep is used as an "or"

Question 32

egrep 'no(b|n)'

Answer 32

() acts as a scope for |, searching for nob or non

Question 33

grep [#-#]

Answer 33

The [ ] characters can also be used to match a single character. However, unlike the period character . the [ ] characters are used to specify exactly what character you want to match. For example, if you want to match a numeric character, you can specify [0-9]

Question 34

grep [#-#]{#}

Answer 34

You can use { } characters with a number to express that you want to repeat a pattern a specific number of times; for example: {3}.

Question 35

wc -l -w

Answer 35

word count, # of lines, # of words

Question 36

vi :q!

Answer 36

quit without save changes in vi

Question 37

vi :wq

Answer 37

save changes and quit

Question 38

command that displays basic computer hardware

Answer 38

lscpu

Question 39

command for how much ram/swap space

Answer 39

free -g / -m (gb mb respectively)

Question 40

command for pci slot info

Answer 40

lspci

Question 41

lspci -k

Answer 41

-k shows kernal driver info

Question 41

find all usb connected devices

Answer 41

lsusb

Question 42

show kernal drivers used to run linux

Answer 42

lsmod

Question 43

fdisk

Answer 43

find disks

Question 44

fdisk -l

Answer 44

When the -l option is used with fdisk, then the command will non-interactively list block devices, which includes disks (hard drives) and logical volumes.

Question 45

Which commands will check hard disk MBR partitions?

Answer 45

fdisk sfdisk cfdisk

Question 45

Which commands will check hard disk GPT partitions?

Answer 45

gdisk cgdisk sgdisk

Question 46

ps

Answer 46

shows some running processes

Question 47

pkill

Answer 47

kills by process

Question 48

ps -e

Answer 48

shows all processes

Question 49

ps -o

Answer 49

specify which columns to output

Question 50

free

Answer 50

, the free command will show overall system memory usage:

Question 51

ps aux

Answer 51

shows everything running in system

Question 52

ps -f

Answer 52

shows extra info about things running in system

Question 53

syslogd

Answer 53

The logging daemon on recent Linux distributions based on systemd

Question 54

sbin

Answer 54

system binaries, under root, /

Question 55

ping -c

Answer 55

-c is the number of times per ping, e.g. -c4 for 4 pings

Question 56

dig

Answer 56

domain name finder

Question 57

dig -x

Answer 57

use an IP address to look up a fqdn

Question 58

netstat

Answer 58

network statistics, Displays active network connections: Shows which services are listening on which ports, and the status of open connections (e.g., LISTEN, ESTABLISHED). Shows routing tables: Provides the routing table used by the system to determine how to route packets to different network destinations. Displays interface statistics: Shows information about the network interfaces, including the number of packets sent and received.

Question 59

netstat -t

Answer 59

tcp sockets for netstat

Question 60

netstat -l

Answer 60

listening for sockets on netstat

Question 61

netstat -n

Answer 61

the numbers or ip address numbers are listed

Question 62

ss

Answer 62

ss command to view which connections are currently established between the local machine and remote machines, statistics about those connections, etc.

Question 63

id

Answer 63

shows user id, gid

Question 64

getent

Answer 64

The getent command has the advantage over the grep command as it is also able to access user accounts that are not defined locally. (servers)

Question 65

output of /etc/passwd

Answer 65

name:password:UID:GID:Comment:directory:shell

Question 66

who

Answer 66

Use the who command to get the current list of users on the system:

Question 67

w

Answer 67

Use the w command to get a more detailed view of the users who are currently on your system:

Question 68

id -g

Answer 68

show current users group

Question 69

groupadd -r

Answer 69

-r is the reserved range, 1-999

Question 70

groupmod -n

Answer 70

change name of a group

Question 71

groupmod -g

Answer 71

change group GID

Question 72

useradd -D

Answer 72

The -D option to the useradd command will allow you to view or change some of the default values used by the useradd command.

Question 73

useradd -m

Answer 73

Make sure that their home directory will be created by specifying the -m option.

Question 74

usermod -L

Answer 74

usermod -L student command could be used to "lock" the account.

Question 75

usermod -U

Answer 75

The account could be unlocked with the usermod -U student command.

Question 76

usermod -g / -G

Answer 76

option for the usermod command can be used to specify a user's group ID (either primary or secondary)?

Question 77

UID 1-499

Answer 77

System users

Question 78

ls -a

Answer 78

list hidden files

Question 79

The setuid permission...

Answer 79

...allows a command to be run as the file owner.

Question 80

The setgid permission...

Answer 80

...allows a command to be run as the group owner of the file. ...allows files created in a directory to be owned by the group that owns the directory.

Question 81

useradd -d

Answer 81

specifies the home directory of the user

Question 82

/tmp

Answer 82

temporary usage filesystem that is refreshed each reboot

Question 83

man -k

Answer 83

keyword option for man pages

Question 84

hide a file in linux

Answer 84

To hide a file in the Linux filesystem, simply rename it with a prefixed dot (.) to its filename. Therefore, mv password.txt .password.txt will cause the file password.txt to be renamed as a "dot" file and become hidden from the ls command.

Question 85

tail -c

Answer 85

The -c option is used with tail to print only the last X bytes of data to the screen.

Question 86

what does /sys do

Answer 86

The /sys virtual filesystem is used to interact with the kernel and system as a whole. It did not provide any method to interact with individual processes and was created to move some of the original functions from /proc to /sys to clean up the /proc structure.

Question 87

isofs

Answer 87

The ISO File System (isofs) is a file system for optical disc media. Being published by the International Organization for Standardization (ISO), the file system is considered an international technical standard. Since the specification is available for anybody to purchase, implementations have been written for many operating systems, including Linux.

Question 88

free

Answer 88

free storage left

Question 89

Which GID is usually used to represent the root group on a Linux system?

Answer 89

0

Question 90

umask

Answer 90

The umask command is used to change the default permission for files and directories at the time of the file's creation.

Question 91

useradd -M

Answer 91

The -M option creates a user without a home directory using useradd. When the -m option is used, the user's home directory will be created using the system's default setup and template.