Basics

Question 1

View Specific Disk Partition

Answer 1

fdisk -l /dev/sda

Question 2

View all Disk Partitions

Answer 2

fdisk -l

Question 3

Find Out Top File Sizes

Answer 3

find -type f -exec du -Sh {} + | sort -rh | head -n 5

Question 4

Disk space usage: Exclude Certain File System Type

Answer 4

df -x ext3

Question 5

Disk space usage: Display Certain File System Type

Answer 5

df -t xfs

Question 6

Display File System Inodes

Answer 6

df -i

Question 7

File space usage: grand total for each argument

Answer 7

du -ch

Question 8

File space usage: summary of a grand total disk usage size

Answer 8

du -sh

Question 9

File space usage: displays the number of disk blocks

Answer 9

du

Question 10

list running services

Answer 10

systemctl list-units --type=service --state=running

Question 11

rpm package manager
query all packages

Answer 11

rpm -qa

Question 12

kernel parameters

Answer 12

sysctl -a

Question 13

display the largest folders/files including the sub-directories

Answer 13

du -Sh | sort -rh | head -5

Question 14

how to handle this:
> $ sudo echo ‘127.0.0.1 bob’&raquo_space; /etc/hosts
zsh: permission denied: /etc/hosts

Answer 14

> $ echo ‘127.0.0.1 bob’ | sudo tee -a /etc/hosts
[sudo] password for gludwig:
127.0.0.1 bob

Question 15

all Available fdisk Commands

Answer 15

fdisk /dev/sda

Question 16

rsync: Count files recursively through directories

Answer 16

rsync –stats –dry-run -ax /etc /test

rsync –stats –dry-run -ax .

Question 17

all File System Disk Space Usage

Answer 17

df -a

Question 18

compile options

Answer 18

cat /boot/config-$(uname -r)

Question 19

loaded kernel modules

Answer 19

lsmod
is a trivial program which nicely formats the contents of the /proc/modules, showing what kernel modules are currently loaded.

Question 20

generate password having length 64

Answer 20

mkpasswd -l 64

Question 21

Find Top 15 Processes by Memory Usage

Answer 21

top -b -o +%MEM | head -n 22

Question 22

cat | cut

Answer 22

cat report.csv |cut -f 5-11,13- -d’,’ > cleanreport.csv

Question 23

cat | sudo tee

Answer 23

cat

Question 24

> new_file

Answer 24

> new_file
text text
^C

Question 25

Disk space usage: display type

Answer 25

df -Thl

Question 26

contents of an initramfs image

Answer 26

sudo lsinitrd

Question 27

kernel ring messages

Answer 27

dmesg -T

Question 28

which packages provides a tool

Answer 28

dnf whatprovides mkpasswd

Question 29

search largest folder

Answer 29

sudo du -hax --exclude="./usr/lib" / | sort -r -h | head -30 2> /dev/null

Question 30

copy with attributes remaining

Answer 30

cp -a

Question 31

full shell login

Answer 31

su -l

Question 32

count of searched words in files

Answer 32

grep -r SEARCHED_WORD | wc -w

Question 33

list file names in which the searched word is found

Answer 33

grep -l SEARCHED_WORD

Question 34

list active services

Answer 34

systemctl list-units --type=service --state=active

Question 35

list enabled services

Answer 35

systemctl list-unit-files | grep enabled

Question 36

rpm package manager | list all files in a package

Answer 36

rpm -ql package_name

Question 37

rpm package manager | find package which provides a files

Answer 37

rpm -qf $(which kill) similar to: dnf whatprovides kill

Question 38

print a sequence of numbers | with equal width from 0 to 10 step 2

Answer 38

seq -w 0 2 10

Question 39

print a sequence of numbers | comma separated from 1 to 100 step 1

Answer 39

seq -s, 1 1 100

Question 40

write consecutive numbers from 0 to 9 in two columns

Answer 40

seq -w 0 9 | paste - -

Question 41

grep: invert search result

Answer 41

grep -v SEARCH_TERM

Question 42

grep empty lines

Answer 42

grep '^$'

Question 43

grep file content without empty lines

Answer 43

cat sample.txt | grep -v '^$'

Question 44

find all files recursively in the current directory where the file's name start with "foo"

Answer 44

find . -name "foo*"

Question 45

jq: return all of the elements of an array

Answer 45

cat example.json | jq '.[]'

Question 46

jq: return the first element of an array

Answer 46

cat example.json | jq '.[0]'

Question 47

jq: get multiple fields from the second element

Answer 47

cat example.json | jq '.[1] | {name: .company.name, lat: .address.geo.lat}'

Question 48

calculate 5! on bash

Answer 48

echo {1..5} | tr ' ' '*' | bc

Question 49

Find Which Process Accessing a Directory

Answer 49

fuser -v .

Question 50

Find Which Process Accessing .bashrc

Answer 50

fuser -v -m .bashrc

Question 51

kill a processes accessing a directory interactively

Answer 51

sudo fuser -ki .

Question 52

rename .txt into .txt_log | .txt to .txt_log for all *.txt

Answer 52

rename .txt .txt_log *.txt

Question 53

report a snapshot of the current processes | UNIX style, all processes, long format, full-format listing

Answer 53

ps -elf

Question 54

report a snapshot of the current processes | BSD style, all processes with a terminal (tty), all processes owned by you

Answer 54

ps ax

Question 55

report a snapshot of the current processes | BSD style, all processes with a terminal (tty), all processes owned by you, user-oriented format

Answer 55

ps aux

Question 56

report a snapshot of the current processes | BSD style, all processes with a terminal (tty), all processes owned by you, only running processes

Answer 56

ps axr

Question 57

report a snapshot of the current processes | GNU style, all processes, as tree

Answer 57

ps -e --forest

Question 58

report a snapshot of the current processes | UNIX style, extra full format

Answer 58

``` ps -F # RSS: resident set size == used RAM ```

Question 59

report a snapshot of the current processes | UNIX style, all processes, long format, don't show flags, show rss

Answer 59

``` ps -ely # RSS: resident set size == used RAM ```

Question 60

print a process tree | UNIX style

Answer 60

ps -ejH

Question 61

print a process tree | BSD style

Answer 61

ps axjf

Question 62

report a snapshot of the current processes | UNIX style, info about threads

Answer 62

ps -eLf

Question 63

report a snapshot of the current processes | BSD style, info about threads

Answer 63

ps axms

Question 64

report a snapshot of the current processes | UNIX style, add security data

Answer 64

ps -eM

Question 65

report a snapshot of the current processes | BSD style, add security data

Answer 65

ps axZ

Question 66

report a snapshot of the current processes | get every process running as root (real & effective ID)

Answer 66

ps -U root -u root u

Question 67

report a snapshot of the current processes | only the process IDs of syslogd

Answer 67

ps -C syslogd -o pid=

Question 68

get the process IDs of sshd

Answer 68

pgrep sshd

Question 69

report a snapshot of the current processes | Print only the name of PID 42

Answer 69

ps -q 42 -o comm=

Question 70

display a tree of processes | show command line parameters

Answer 70

pstree -a

Question 71

ping a range of ip addresses in one go

Answer 71

for ((i=1;i<10;i++)); do ping -c 1 -w 1 8.$i.8.8 &> /dev/null && echo 8.$i.8.8 is alive; done

Question 72

Edit Command Line in Your Editor

Answer 72

CTRL+X CTRL+E

Question 73

remove duplicate lines

Answer 73

awk '!seen[$0]++' file

Question 74

print output in columns

Answer 74

mount | column -t

Question 75

print output in columns, use ":" as separator

Answer 75

cat /etc/passwd | column -t -s :

Question 76

rewrite mv /tmp/working-dir/readme.md /tmp/working-dir/readme.md.backup using brace ticks

Answer 76

``` mv /tmp/working-dir/readme.md{,.backup} # everything in the brace gets replaced and the prefix is put in front ```

Question 77

print the command to copy a1.txt - a9.txt to backup

Answer 77

echo cp a{1..9}.txt backup-dir

Question 78

add Google public IPv4 DNS server

Answer 78

vi /etc/resolv.conf | nameserver 8.8.8.8

Question 79

create a file with a random part

Answer 79

mktemp file_name.XXXX

Question 80

create a directory with a random part

Answer 80

mktemp -p dir_name.XXXX

Question 81

find port numbers

Answer 81

cat /etc/services

Question 82

scp is replaced with rsync: | copy file 'foo.txt' to 'me@server:/home/me/'

Answer 82

rsync foo.txt me@server:/home/me/

Question 83

scp is replaced with rsync: | copy folder 'bar' to 'me@server:/home/me/'

Answer 83

rsync -r bar/ me@server:/home/me/

Question 84

rsync: symbolic links skipped by default | copy folder'bar' to 'me@server:/home/me/' with symlinks

Answer 84

rsync -r --links bar/ me@server:/home/me/ or rsync -a bar/ me@server:/home/me/

Question 85

rsync: | copy file 'foo.txt' to 'me@server:/home/me/' and specify a non-ssh port (8022)

Answer 85

``` rsync -e 'ssh -p 8022' foo.txt me@server:/home/me/ or update the ~/.ssh/config file: Host server Port 8022 ```

Question 86

journalctl: | Jump to the end of the journal (-e), and enable follow mode (-f)

Answer 86

journalctl -ef

Question 87

journalctl: | filter for a unit

Answer 87

journalctl _SYSTEMD_UNIT=sshd.service

Question 88

journalctl: | display all messages generated by, and about, the sshd.service systemd unit

Answer 88

journalctl -u sshd.service

Question 89

journalctl: | all messages in the journal with a priority in the range emerg up to and including err

Answer 89

journalctl -p emerg..err

Question 90

journalctl: | all messages up to and including that level are displayed

Answer 90

journalctl -p err

Question 91

journalctl: Only show messages from the last system boot. This is useful for searching for information about a system crash. This requires a persistent journal to be configured.

Answer 91

on Centos journalctl -b -1 #on Debian journalctl -b

Question 92

journalctl: | with start and end date

Answer 92

journalctl --since "2015-02-02 20:30:00" --until "2015-03-31 12:00:00"

Question 93

journalctl: | verbose

Answer 93

journalctl -o verbose

Question 94

journalctl: | check

Answer 94

journalctl --verify

Question 95

journalctl: | enable user to read log entries

Answer 95

sudo usermod -aG systemd-journal BENUTZERNAME

Question 96

journalctl: | in UTC

Answer 96

journalctl --utc

Question 97

journalctl: | list boots

Answer 97

journalctl --list-boots

Question 98

journalctl: | by PID

Answer 98

journalctl _PID=8088

Question 99

journalctl: | kernel messages

Answer 99

journalctl -k

Question 100

journalctl: | by priority

Answer 100

``` journalctl -p err # 0: emerg # 1: alert # 2: crit # 3: err # 4: warning # 5: notice # 6: info # 7: debug ```

Question 101

journalctl: | print all to stdout

Answer 101

journalctl --no-pager

Question 102

journalctl: | as json

Answer 102

journalctl -o json | journalctl -o json-pretty

Question 103

journalctl: | only 20 log entries

Answer 103

journalctl -n 20

Question 104

journalctl: | disk usage

Answer 104

journalctl --disk-usage

Question 105

journalctl: | shrink by size

Answer 105

journalctl --vacuum-size=1G

Question 106

journalctl: | shrink since

Answer 106

journalctl --vacuum-time=1years

Question 107

linux namespace types

Answer 107

``` UTS: Hostname and NIS domain name Cgroup: Controls the system resources (like CPU, Memory…) the process can use. IPC: POSIX message queues Network: Network devices, stacks, ports, etc. Mount: Mount points PID: Process IDs Time: Boot and monotonic clocks User: User and group IDs ```

Question 108

how to get the return code of a program ran in the shell?

Answer 108

echo $?