Linux

Question 1

Check memory usage

Answer 1

free -h shows all free memory

du -h -d 1 (disk usage, human, depth =1) meaning the depth of folders it will look.

df -h shows how much memory each directory is consuming in human readable form

Du -a -h -d 1 shows you all the files, hidden files, and directories disk usage

Question 2

Find text in a directory

Answer 2

grep /path/to/file -e text-to-search

grep /path/to/dir -e text-to-search

grep -rnw /path/to/dir -e text-to-search

• r or -R is recursive,
• n is line number, and
• w stands for match the whole word.
• l (lower-case L) can be added to just give the file name of matching files.
• e is the pattern used during the search

Question 3

Read file to console

Answer 3

cat

Question 4

Open file to edit

Answer 4

vim

Question 5

In vim

quit file, save quit, edit file, how to stop editing

Answer 5

:q!, :q, :wq, [i] for insert, escape to stop editing

Question 6

print files in dir

Answer 6

ls, ls -al shows all hidden files with permissions

Question 7

move file, make directory, remove directory, make file

Answer 7

mv file1 file2
mkdir dirName
rmdir dirName
touch file

Question 8

find a file

Answer 8

find /dir/ -name file.txt

searches for the file in the dir and sub dirs

Question 9

read beginning or end of files

Answer 9

head -n file.txt

tail -n file.txt

Question 10

See differences between 2 files

Answer 10

diff file1 file2

Question 11

remove file, remove directory, remove directory and all sub files/dirs

Answer 11

rm file, rmdir dirname, rm -rf dirname

Question 12

create a tar file, unzip a tar file

Answer 12

tar -cvf name.tar dirname/or/filename

• c create tar
• v verbose
• f specify file name

tar -xzf tar.gz

• x extract
• z gzip, gunzip, ungzip,
• f file

Question 13

change read-write permissions, change owner

Answer 13

chmod filename

chown newowner:newgroup filename

Question 14

show all jobs running and their statuses. Jobs are started by the shell

Answer 14

jobs

Question 15

stop a process

Answer 15

kill -9/-15 PID

Question 16

download a file given a link

Answer 16

wget download-link

Question 17

check linux system information such as machine name, operatin system, kernel

Answer 17

uname

cat /proc/cpuinfo

Question 18

task manager but for linux

Answer 18

top

Question 19

see a list of previous commands run

Answer 19

history

Question 20

get a list/help with linux commands

Answer 20

man

Question 21

check ip address

Answer 21

ip addr

hostname -i

Question 22

how to copy a file, directories, while preserving file state?

Answer 22

cp file1 file2 – copies file1 to file2

cp file1 file2 new – copies file1/file2 into new dir

cp -R dir1 dir2 – copies all files from dir1 into dir2. If dir2 exists it will make a subdir of dir1 in dir2, if it does not exist it will create dir2

-p option preserves all information about the file, time of last edit, permissions, ect

Question 23

monitor a process on the system

Answer 23

ps aux | grep

Question 24

do 2 tasks at once in a single line

Answer 24

use &&

cd /home && ls - al
cd’s to home and executes ls -al

Question 25

how to use scp on, copy a file from a remote location or copy to a remote location

Answer 25

Linux file -> windows
Scp user@domain:
Windows -> linux
Scp user@domain:

**to go from linux to windows, you need to set up an scp server on windows. This is not default

Question 26

check network traffic

Answer 26

tcpdump

tcpdump -i any
or

there are many ways to use this command

Question 27

list of linux file permissions you can set
example:
chmod filename

Answer 27

400: Gives the user read permission, and removes all other permission. These permissions are specified in octal, the first char is for the user, second for the group and the third is for other
755: means read and execute access for everyone and also write access for the owner of the file. … So, there should be no permission to everyone else other than the owner to write to the file, 755 permission is required.

Question 28

sed, stream editor command

Answer 28

https://www.geeksforgeeks.org/sed-command-in-linux-unix-with-examples/

$cat > geekfile.txt
unix is great os. unix is opensource. unix is free os.
learn operating system.
unix linux which one you choose.
unix is easy to learn.unix is a multiuser os.Learn unix .unix is a powerful.
Sample Commands

Replacing or substituting string : Sed command is mostly used to replace the text in a file. The below simple sed command replaces the word “unix” with “linux” in the file.

$sed ‘s/unix/linux/’ geekfile.txt

this replaces the first ‘unix’ per line with ‘linux

$sed ‘s/unix/linux/g’ geekfile.txt
makes replacements for all found characters

$sed ‘s/unix/linux/3g’ geekfile.txt
replaces the 3rd