WLSS

Question 1

Debian Network Settings (persistent and non-persistent)

Answer 1

Via ip commands

• ip link
• ip addr
• ip route
  Persistent via

1. ifupdown
   
   1. /etc/network/interfaces
2. systemd-networkd
3. NetworkManager (GUI)

Question 2

RHEL Network Settings (persistent and non-persistent)

Answer 2

Via ip commands

• ip link
• ip addr
• ip route

Persistent via

• nmtui
• nmcli
• /etc/sysconfig/network-scripts/ifcfg-<device></device>

Question 3

Applying the network config changes on Debian and RHEL

Answer 3

Debian:

• /etc/network/interfaces: ifdown <device> and ifup <device>
• systemd-networkd: networkctl reload

RHEL:

• nmcli connection up <device>

Question 4

what will this do?
> find . -name h*

Answer 4

find files and directories starting with letter h starting from current working directory

Question 5

What is *,?,[abcd],[a-d],[^ab] or [!ab]

Answer 5

Filename Expansion:
* = 0 (inclusive!!) or more characters
? = exactly 1 character
[abcd] = exact 1 character, but only those that are listed
[a-d] = exact 1 character, but only those within the given range (here: a until d)
[^ab] = exact 1 character, EXCEPT these letters

Question 6

What is {a,b,c},{0..6} and {0..6..2}

Answer 6

Brace expansion:
{a,b,c} : Generate each of the listed characters (here: a, b, c)
{0..6} : Generate each of the characters with the given range (here: 0,1,2,3,4,5,6)
{0..6..2}: Generate each of the characters with the given range, with an increment (here: 0,2,4,6)

⇒ No need to match existing filenames.

Question 7

what is $()

Answer 7

notation of command substitution
~$ du /etc > log-$(date +%Y-%m-%d)
~$ ls
log-2017-09-29

Question 8

what is the notation of command substitution and what is the use

Answer 8

$( ) => Use output of commands

Question 9

What is $(( ))

Answer 9

Arithmetic expansion:
~$ a=5
~$ b=4
~$ echo De som is $((a+b))
De som is 9

Question 10

What is arithmetic expansion notation and what does it do?

Answer 10

$(( )) => does calculations

Question 11

What do these do?
command 2>&1 >/dev/null

Answer 11

command 2>&1 >/dev/null:
Redirect output to trash and write errors to standard output
Thus: only keep the errors and be able to do something with it via e.g. pipes

Question 12

What are the different shells?

Answer 12

• **bash****
  
  • Based on original Bourne shell, sh and implements useful features from ksh and csh
• **tcsh****
  
  • Syntax resembles more C language, derivative of original csh (Berkely Unix C Shell)
• **dash:** Debian Almquist shell
  
  • Aims to be as small as possible, default non-interactive shell in Ubuntu/Debian
• **zsh:** Z shell
  
  • Extended Bourne shell, Default shell in macOS Catalina and Kali 2020.4
• Others:
  
  • **ksh:**** Korn shell
  • **fish:** friendly interactive shell

Question 13

where are all shells listed?

Answer 13

/etc/shells

Question 14

how to change user login shell?

Answer 14

chsh or usermod --shell <shell> <user>

Question 15

where is login shell for each user stored?

Answer 15

/etc/passwd

Question 16

What shell am I currently running? (command)

Answer 16

ps -p \$\$ or $0

Question 17

what is $SHELL

Answer 17

Default shell, NOT the one running

Question 18

what is the restricted shell?

Answer 18

rbash or bash -r (easy to bypass)

Question 19

/usr/sbin/nologin

Answer 19

Not listed in /etc/shells

⇒ When assigned as default shell, user cannot use interactive shell

<aside>
💡 it makes sense to use nologin when u want to make user that can use e.g. ftp or sftp (so it has valid, unlocked password), but not log in to the machine to do work on it.

</aside>

Question 20

/etc/nologin

Answer 20

if exists and readable, login will allow access only to root.
=> Temporarily disabling all unprivileged logins