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RHCSA Commands > Processes > Flashcards

Processes Flashcards

1
Q

What are the different process states?

A

R: running
Z: Zombie (including Z, X)
T: Stopped
S: Sleeping (including S, D, K, I)

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2
Q

ps aux

A

displays all processes including processes without a controlling terminal

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3
Q

ps lax

A

long listing (lax options) provides more detail, and gives faster results by avoiding username lookup

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4
Q

display the processes in a tree format

A

ps –forest

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5
Q

display the list of jobs for the shell’s session

A

jobs

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6
Q

bring a background job to the foreground

A

fg %1

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7
Q

displays information about jobs.

A

ps j

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8
Q

when running the “ps j” command, one job has the + sign. explain

A

sign indicates that this job is the current default

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9
Q

when running the “ps j” command, one job has the - sign. explain

A

The - sign indicates the previous job that will become the default job when the current default job finishes.

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10
Q

List the signals available

A

kill -l

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11
Q

Common signals

A

1: HUP
3: QUIT
9: KILL
15: TERM (default)
18: CONT
19: STOP

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12
Q

List all processes related to user bob

A

pgrep -l -u bob

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13
Q

Kill all processes related to user bob

A

pkill -SIGKILL -u bob

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14
Q

Find all terminals that bob is logged in from

A

w -u

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15
Q

Kill all processes related to a given terminal

A

pkill -SIGKILL -t tty2

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16
Q

Which signals are recommended and in which order?

A

SIGTERM
SIGINT
SIGKILL

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17
Q

kill multiple processes, based on their command name

A

killall

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18
Q

To terminate background job

A

kill -SIGTERM %1

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19
Q

What is pts/1

A

1) pseudo-terminals
2) emulated terminals: xterm, Gnome, SSH etc.

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20
Q

What is tty/2

A

1) TTY: direct interfaces with the kernel.
2) Traditionally physical terminals,
3) Originally teletypewriters, connected directly to the system.
4) Nowadays, virtual consoles accessed typically through key combinations like Ctrl+Alt+F1 to F6.
5) multi-user.target, rescue.target, emergency.target

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21
Q

display the current load average

A

uptime, top

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22
Q

Show cpus

A

lscpu

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23
Q

lists active currently loaded service units

A

systemctl list-units --type=service

24
Q

lists all currently loaded service units

A 
systemctl list-units --type=service --all
25
Q

lists units that are both loaded and active

A

systemctl

26
Q

View a unit’s status with the systemctl

A 
systemctl status sshd.service
27
Q

verify whether a service unit is active

A

systemctl is-active sshd.service

28
Q

verify whether a service unit is enabled to start automatically during system boot

A

systemctl is-enabled sshd.service

29
Q

verify whether the unit failed during startup,

A

systemctl is-failed sshd.service

30
Q

list all failed services

A

systemctl --failed --type=service

31
Q

List all socket units, active and inactive

A 
systemctl list-units --type=socket --all
32
Q

Start service

A

systemctl start sshd

33
Q

Stop service

A

systemctl stop sshd

34
Q

Restart service

A

systemctl restart sshd

34
Q

Reload service

A

systemctl reload sshd

35
Q

Start or reload service

A

systemctl restart-or-reload service

36
Q

displays the hierarchy of dependencies to start a service unit

A

systemctl list-dependencies sshd.service

37
Q

Mask sendmail service

A

systemctl mask sendmail.service

38
Q

Unmask a service

A

systemctl unmask sendmail

39
Q

Configure a service to start at boot

A

systemctl enable sshd

40
Q

Configure a service to start now and at boot

A

systemctl enable –now sshd

41
Q

display a list of users that are currently logged in to the system

A

w

42
Q

Where do you set StrictHostKeyChecking

A

in ~./ssh/config. or /etc/ssh/ssh_config

43
Q

display a list of users that are currently logged in to the system while showing where user is logged in from

A

w –from

44
Q

configure your account for passwordless access

A 
ssh-copy-id -i .ssh/key-with-pass.pub user@remotehost
45
Q

start ssh-agent

A

eval $(ssh-agent)

46
Q

What is the use of ssh-agent

A

cache ssh keys passwords

47
Q

How do you add keys to ssh-agent?

A

ssh-add

48
Q

Trubleshoot ssh

A

ssh -v -i key user@remoteserver

49
Q

risks of allowing direct login as the root user

A

1) root user exists on every Linux system, so attacker needs only to guess the password

2) root user has unrestricted privileges, so its compromise can lead to maximum damage

3) From an auditing perspective, it is hard to track which authorized user logged in as the root user

50
Q

prohibit root user to ssh in

A

echo 'PermitRootLogin no' >> /etc/ssh/sshd_config

51
Q

prevent password-based authentication but to allow private key-based authentication for root

A

echo 'PermitRootLogin without-password' >> /etc/ssh/sshd_config

52
Q

Advantages of disabling password authentication

A

1) Prevent password-guessing attacks

2) Attacker needs both the passphrase and a c private key.

53
Q

Disable password bassed login

A

echo 'PasswordAuthentication no' > /etc/ssh/sshd_config

54
Q

Enable ssh authentication for user

A

ensure that the user’s ssh key is in ~/.ssh/authorized_keys

RHCSA Commands (23 decks)

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