This is my notes about Linux

Linux

Podman is a daemonless, open source, Linux native tool designed to make it easy to find, run, build, share and deploy applications using Open Containers Initiative (OCI) Containers and Container Images.

Questions?
- What is demonless and what difference does it make? - Learn OCI standards?

Podman relies on an OCI compliant Container Runtime (runc, crun, runv, etc) to interface with the operating system and create the running containers.
Podman Network Podman Docs

There is a List of TUI tools - list - aWlist - bigAWlist_ - List of Terminal Tools - x-cmd very interesting - unix-modern command line tool - Coding Interview University - Awesome Shell - DevOps-exe - test-your-sysadmin-skills - DevOps-Guide - devops-resources - awesome-scalability - Cloud-DevOps-Learning-Resources - 100-GO
-The GNU Coreutils Package -Enterprise Integration Patterns

-https://the-algorithms.com/language/go

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Project :

Interview Questions

Answer Theses Questions Daily with Writing down Answers :

1.What function does DNS play on a network?

this is the why ~~strike~~

sadia

ParadeDB is a modern Elasticsearch alternative built on Postgres.

HTTP/1.0 From Scratch

locate -- updatedb commnad find fzf batcat is bat in debian based systems

cntrl + D stopp the current standard input cntrl + C terminate

GDK_BACKEND=x11 surf https://example.com

use surf browser

There is a software eng roadmap on youtube bytecode

Our recommended materials to crack your next tech interview.

Coding - Leetcode - Cracking the coding interview book - Neetcode

System Design Interview - System Design Interview book 1, 2 by Alex Xu - Grokking the system design by Design Guru - Design Data-intensive Application book

Behavioral interview - Tech Interview Handbook (Github repo) - A Life Engineered (YT) - STAR method (general method)

OOD Interview - Interviewready - OOD by educative - Head First Design Patterns Book

Mock interviews - Interviewingio - Pramp - Meetapro

Apply for Jobs - Linkedin - Monster - Indeed

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Tmux collaboration This is serverless website

Next we might want to see how the system booted and what kernel parameters were passed when the system was started.

cat /proc/cmdline

vmstat 1 5 mpstat 2 5 ps -ef | awk '{print $1}' | sort | uniq -c pidstat 1 5 iostat -xz 1 5 Solution Solution Let's look at the network usage and load of the system.

sar -n DEV 1 5

What are you seeing here? What devices are showing up? Do any devices seem to be under high load? Which one has the most traffic?

Next we check tcp packets and errors.

sar -n TCP,ETCP 1 5

Do we appear to be seeing any large numbers of errors? Why might retransmits be a big problem?

Next we will check how many packages are on the system.

dpkg -l | wc -l

Solution Check disk information and count partitions

fdisk -l | grep -i vd

Why did we use VD?

Let's use another command to see that information another way.

lsblk

and

blkid

mount | grep vda

for type in $(ls /dev/disk); do echo "type is $type"; ls -l /dev/disk/$ type; done

Let's make a giant file filled with 0's and then check available space.

dd if=/dev/zero of=/root/bigfile bs=1024k count=3000

ip addr | grep enp | grep mtu | awk '{print $2}' | sed 's/://' > /root/interface write an ansible playbook to gather information What is the ip of your interface?

ip addr | grep enp | grep inet | awk '{print $2}' ip route | grep -i default | awk '{print $3}'

Check network throughput to your system for 20 seconds

ifstat 2 10

Solution Solution

Check network throughput to your system for 20 seconds

ifstat 2 10

Note: There is very little traffic (in size) into or out of your system.

Do a tcpdump to inspect the actual traffic into your system. Capture 1000 packets against your enp1s0 interface.

tcpdump -ni enp1s0 -s0 -c 1000

Let's generate a .pcap file that can be used by wireshark to inspect traffic. (We don't have wireshark on this system)

for i in $(seq 1 5); do ping -c 10 www.google.com & done; tcpdump -ni enp1s0 -s0 -c 200 -w $(hostname).pcap

Verify the size and creation of the file.

ls -lh /root/ubuntu.pcap

Check your connection to node01.

ssh node01

Type in exit to return to the original system

exit

Check system uptime and one layer of debug1.

ssh -v node01 'uptime'

What additional information was shown with the -v option? (debug1)

ssh -vv node01 'uptime'

What additional information was shown with the -vv option? (debug2)

ssh -vvv node01 'uptime'

What additional information was shown with the -vvv option (debug3)

So we looked at a ssh connection over to node01. You should note that the keys are being used and that is why no password was asked to connect. We'll explore that more shortly.

What are the difference between printenv env declare -p set

tell the difference?

Can you capture whether or not processes are running? Test for httpd and sshd.

ps -ef | grep -i [h]ttpd httpdCheck=$(echo $?)

ps -ef | grep -i [s]shd sshdCheck=$(echo $?)

time apt upgrade -y

The chroot lab of Scott was good it was a way How to cerate JumpSever virt-what

dmidecode | grep -iE "virt|prod" systemd-analyze time systemd-analyze blame systemd-analyze critical-chain ssh.service

IT-gruundshutz BSI: IT-Grundschutz

BSI

calmAV anti virus

Grafana Installation Guide: Refer to the Grafana Docs for latest installation instructions.

Install the required packages and Grafana GPG key.

apt install -y apt-transport-https

apt install -y software-properties-common wget

sudo wget -q -O /usr/share/keyrings/grafana.key https://apt.grafana.com/gpg.key

Add the Grafana repository.

echo "deb [signed-by=/usr/share/keyrings/grafana.key] https://apt.grafana.com stable main" | sudo tee -a /etc/apt/sources.list.d/grafana.list

Finally, we're ready to install Grafana:

apt update

Install the latest Enterprise release:

apt install -y grafana-enterprise

Now that you've installed Grafana, let's make sure it's started.

sudo systemctl daemon-reload sudo systemctl start grafana-server sudo systemctl status grafana-server --no-pager

Verify that the server is serving on port 3000 (the default port)

systemctl status grafana-server --no-pager ss -ntulp | grep grafana ss -ntulp | grep 3000

We can also check that the external Web UI is available and change the default password.

https://5cc6e7db-6fd0-4330-8a9b-a690d3ead415-10-244-6-90-3000.spch.r.killercoda.com

Change the password. Default User: admin and Password: admin

Feel free to look around in the Web UI and then continue on to the next part of the lab.

Hashicorp certc

We look at important Vim settings if you like to work with YAML during the K8s exams. Settings

First create or open (if already exists) file .vimrc :

vim ~/.vimrc

Now enter (in insert-mode activated with i) the following lines:

set expandtab set tabstop=2 set shiftwidth=2

Save and close the file by pressing Esc followed by :x and Enter. Explanation

Whenever you open Vim now as the current user, these settings will be used.

If you ssh onto a different server, these settings will not be transferred.

Settings explained:

expandtab: use spaces for tab tabstop: amount of spaces used for tab shiftwidth: amount of spaces used during indentation good site which has DevOps exe: Exp builder

IaC Learn kuber

What are the main pilars of incident response: -Detection -Escalation -Communication -Diagnosis -Repair also there is somrhing like incident retro: -analysis -remidiation -prevention

The standard regaarding these things are incident command system national inident management system

Common terminology Accountability unity of command explicit tranfer of responsibility

Incident Command for IT—What We've Learned from the Fire Department

create severity matrix and the resource allocated to it So the detection starts with monitoring also the scalation should be communicated through means of Jira ...

Set specefic metrics to communicate Observe --> Orient --> decide --> act

QEMU

What Every Programmer Should Know About Memory

A terminal for the modern age█

The difference between apt and apt-get apt

How to concatenate and Join Pdf by pdftk

pdftk 1.pdf 2.pd cat output 12.pdf

What does apt-change log does? can you install different pkg manager on one distro?

The apt change log is a tool used in Debian-based Linux distributions (like Ubuntu) to view the changelog for software packages managed by the Advanced Package Tool (APT). A changelog is a detailed log or record of all notable changes made to a software package. These changes can include bug fixes, new features, security updates, or other modifications.

Check how to figure things out smoothly with tmux and automated script and the role of chils process and these sort of things, the problems occurs when working with tmux and different session.

Some Debian Hardening Material

Official Docs

Before you install any operating system on your computer, set up a BIOS password. After installation (once you have enabled bootup from the hard disk) you should go back to the BIOS and change the boot sequence to disable booting from floppy, CD-ROM and other devices that shouldn't boot. Otherwise a cracker only needs physical access and a boot disk to access your entire system.

This is related to the recovery of root password, in this case how we can Install a new OS or boot

An intelligent partition scheme depends on how the machine is used. A good rule of thumb is to be fairly liberal with your partitions and to pay attention to the following factors: • Any directory tree which a user has write permissions to, such as e.g. /home, /tmp and /var/tmp/, should be on a separate partition. This reduces the risk of a user DoS by filling up your "/" mount point and rendering the system unusable (Note: this is not strictly true, since there is always some space reserved for root which a normal user cannot fill), and it also prevents hardlink attacks. 1 • Any partition which can fluctuate, e.g. /var (especially /var/log) should also be on a separate partition. On a Debian system, you should create /var a little bit bigger than on other systems, because downloaded packages (the apt cache) are stored in /var/cache/apt/archives. • Any partition where you want to install non-distribution software should be on a separate partition. According to the File Hierarchy Standard, this is /opt or /usr/local. If these are separate partitions, they will not be erased if you (have to) reinstall Debian itself. • From a security point of view, it makes sense to try to move static data to its own partition, and then mount that partition read-only. Better yet, put the data on read-only media. See below for more details.

he apt cache) are stored in /var/cache/apt/archives.

The concept of journaling file system

Make a list of services currently running on your system. Try: $ ps aux $ netstat -pn -l -A inet $ /usr/sbin/lsof -i | grep LISTEN Some other tools that can be used for forensic analysis provided in the Debian distribution are: strace and ltrace strace and ltrace how they work and what they do to the system. Some other common tools include ldd (in libc6), strings and objdump (both in binutils)

There is an ebpf tool in windows Windows ebpf RHCA

Set user with exp data sudo usermod -e 2030-03-01 jane Set system account sudo usermod -e "" jane

sudo chage --lastday 0 jane Mark the password for jane as expired to force her to immediately change it the next time she logs in. sudo usermod -a -G developers jane password warning sudo chage -W 2 jane man limits.conf

sudo useradd --system apachedev

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ssh tunnel

ssh -L -R : p ... :p

ssh -D local port destenation host and the set the proxy to the local host on that port ssh tunneling is a good things to learn

cat /etc/services

Read more about ssh tunneling, Read more about TLS, SSL

wq

how to see the details of package with apt ?

apt show command
apt search --names-only search_term
dpkg -s package-name
apt-cache stats
apt show -a

OpenPBS :OpenPBS software optimizes job scheduling and workload management in high-performance computing (HPC) environments – clusters, clouds, and supercomputers – improving system efficiency and people’s productivity. Built by HPC people for HPC people, OpenPBS is fast, scalable, secure, and resilient, and supports all modern infrastructure, middleware, and applications.

watch tower, is to update docker container Macro text editoer

easya ls alternatice

dis systems reading list

some time check openvmm

git work flow: The basic workflow is always the same when I’m working with others: open a branch off of the main branch, start working, commit early & often, push early & often, open a pull request as a draft as soon as possible, finish work, make sure the commits in the branch somewhat make sense, ask for a review, merge.

When I’m working alone, I commit on the main branch 99% of the time and push after each commit.

Sometimes, when working on a branch, I notice that I need to make a new commit in a separate branch so that I can turn it into a separate pull request. There are multiple different strategies that I use here. also i found this article useful: Git stategies

Website of John Ousterhout The courses of operating systems and philosopy of system design also the author of the this

Learn about the backup strategy like incremental backup and ... also look at different file systems and ZFS featurtes ...

How to create 1000 file with size of 5MB

This is my notes about Linux

containerda

Podman is a daemonless, open source, Linux native tool designed to make it easy to find, run, build, share and deploy applications using Open Containers Initiative (OCI) Containers and Container Images.

Questions?
- What is demonless and what difference does it make? - Learn OCI standards?

Podman relies on an OCI compliant Container Runtime (runc, crun, runv, etc) to interface with the operating system and create the running containers.
Podman Network Podman Docs

There is a List of TUI tools - list - aWlist - bigAWlist_ - List of Terminal Tools - x-cmd very interesting - unix-modern command line tool - Coding Interview University - Awesome Shell - DevOps-exe - test-your-sysadmin-skills - DevOps-Guide - devops-resources - awesome-scalability - Cloud-DevOps-Learning-Resources - 100-GO

---

Project :

Interview Questions

Answer Theses Questions Daily with Writing down Answers :

1.What function does DNS play on a network?

this is the why ~~strike~~

backup strategy

The simple method has two backup levels: full and incremental backups. This can be generalized to any number of levels. A full backup would be level 0, and the different levels of incremental backups levels 1, 2, 3, etc. At each incremental backup level you back up everything that has changed since the previous backup at the same or a previous level.

The purpose for doing this is that it allows a longer backup history cheaply. In the example in the previous section, the backup history went back to the previous full backup. This could be extended by having more tapes, but only a week per new tape, which might be too expensive. A longer backup history is useful, since deleted or corrupted files are often not noticed for a long time. Even a version of a file that is not very up to date is better than no file at all.

With multiple levels the backup history can be extended more cheaply. For example, if we buy ten tapes, we could use tapes 1 and 2 for monthly backups (first Friday each month), tapes 3 to 6 for weekly backups (other Fridays; note that there can be five Fridays in one month, so we need four more tapes), and tapes 7 to 10 for daily backups (Monday to Thursday). With only four more tapes, we've been able to extend the backup history from two weeks (after all daily tapes have been used) to two months. It is true that we can't restore every version of each file during those two months, but what we can restore is often good enough.

Learn what is the systemcalls ? The services provided by the kernel to application programs, and the way in which they are invoked

Question: What is Journaling in FS? The services provided by the kernel to application programs, and the way in which they are invokeThe Linux kernel consists of several important parts: process management, memory management, hardware device drivers, filesystem drivers, network management, and various other bits and pieces.
Know that some commands are not executables, but Bash builtins, and that you can get help on them with help and help -d. You can find out whether a command is an executable, shell builtin or an alias by using type command.

- pgrep
- pkill
- pstree -p

good resource to check about shell: good bash guide

which command whatis command whereis command

Make your bash scripts more robust by reliably performing cleanup.

function finish { # your cleanup here. e.g. kill any forked processes jobs -p | xargs kill } trap finish EXIT

Useful git commands:

Git Commands 51. git init – Initialize a git repository 52. git clone repo_url – Clone a repository 53. git status – Show changes 54. git add . – Stage all changes 55. git commit -m "msg" – Commit changes 56. git push origin branch – Push changes 57. git pull origin branch – Pull latest changes 58. git checkout branch – Switch branch 59. git branch -a – List all branches 60. git merge branch – Merge branch into current branch 61. git log --oneline – Show commit history 62. git diff – Show changes 63. git stash – Stash changes 64. git stash pop – Apply stashed changes 65. git reset --hard HEAD~1 – Reset last commit 66. git revert commit_id – Revert commit 67. git tag -a v1.0 -m "Version 1.0" – Create tag 68. git push --tags – Push tags 69. git rm file – Remove a file from git 70. git clean -fd – Remove untracked files 71. git config --global user.name "Your Name" – Set global username 72. git config --global user.email "[email protected]" – Set global email 73. git show commit_id – Show commit details 74. git blame file.txt – Show changes by line 75. git remote -v – Show remote repositories 76. git remote add origin URL – Add remote repo 77. git rebase branch – Rebase branch 78. git cherry-pick commit_id – Pick specific commit 79. git fetch – Fetch remote changes 80. git log --graph – Show graphical commit log 81. git branch -d branch_name – Delete branch 82. git pull --rebase – Rebase while pulling 83. git push --force – Force push changes 84. git reflog – Show reflog 85. git diff HEAD~1 – Show last commit changes 86. git apply patch.diff – Apply patch 87. git reset --soft HEAD~1 – Soft reset 88. git archive --format=tar.gz HEAD > archive.tar.gz – Archive repo 89. git grep "search_term" – Search for text 90. git bisect start – Start binary search 91. git ls-files – List tracked files 92. git update-index --assume-unchanged file – Ignore file temporarily 93. git push origin --delete branch_name – Delete remote branch 94. git pull --all – Fetch all branches 95. git submodule add URL path – Add a submodule 96. git submodule update --init --recursive – Update submodules 97. git commit --amend -m "Updated commit message" – Amend commit 98. git fetch --prune – Remove deleted remote branches 99. git push --mirror destination_url – Mirror repository 100.git worktree add ../branch_name branch_name – Work with multiple branches

User space --> system compontny --? C-libarary standards --> kernel Read about linux system cal every day for a year.

BC sysadmin

DNS is fundamentally a distributed database of hostnames to IP addresses, we manage our database so people know how to get to our site/domain, and somewhere else another person is managing their database so others can get to their domain. These domains are then able to talk to each other and build a massive contact list of the Internet.

what is the different between /etc/shadow and /etc/passwd /etc/sudoer

On systems that use systemd, you can boot into rescue mode by appending systemd.unit=rescue.target to the end of the existing Linux kernel line. At the GRUB splash screen, highlight your desired kernel and press the “e” key to edit its boot options. Similarly, for emergency mode, use systemd.unit=emergency.target. Here’s an example of a typical configuration: linux16 /vmlinuz-3.10.0-229.el7.x86_64 root=/dev/mapper/rhel_rhel-root ro crashkernel=auto rd.lvm.lv=rhel_rhel/swap rd.lvm.lv=rhel_rhel/root rhgb quiet LANG=en_US.UTF-8 systemd.unit=rescue.target Type to start the system after you’ve made your changes.

the user in linux is just a Number UID this UID, the system use API to interact and get info about this user, getpid() function system call is for that

wite a backup script to change the name of thing in date.bck

Introduction 00:35 - Why These Sites Matter 01:08 - 1. VulnHub – Virtual machines with vulnerabilities for hands-on practice 01:46 - 2. Hack The Box – Competitive hacking with real-world challenges 02:35 - 3. Packet Storm Security – Security news and exploit database 03:00 - 4. OverTheWire – Gamified cybersecurity learning 05:17 - 5. Malware Traffic Analysis – Hands-on threat intelligence training 05:41 - 6. Exploit Database – Repository of real-world security vulnerabilities 06:10 - 7. SANS Cyber Aces – Beginner-friendly cybersecurity training 06:30 - 8. Hacking Articles – Ethical hacking tutorials & guides 06:57 - 9. SecurityTube – The YouTube of cybersecurity 07:22 - 10. OpenSecurityTraining – Free courses on reverse engineering & malware analysis 07:46 - 11. CTF Time – Track and join Capture The Flag competitions 08:17 - 12. Intigriti – European-focused bug bounty platform 08:44 - 13. Hack The Army – Ethical hacking challenges for U.S. military systems 09:10 - 14. Replit – Collaborative coding for penetration testing & security scripting 09:38 - 15. CyberDefenders – Hands-on SOC and digital forensics training 10:02 - 16. PortSwigger Web Security Academy – Web application security training 10:30 - 17. TryHackMe – Gamified hacking & guided tutorials 11:10 - 18. Red Team Labs – Advanced red teaming techniques 11:36 - 19. Shodan – The search engine for hackers (finding exposed devices) 12:10 - 20. Bugcrowd University – Learn professional bug bounty hunting 12:36 - 21. Hack This Site – Community-driven ethical hacking challenges 12:59 - 22. Root Me – Interactive cybersecurity challenges 13:32 - 23. Exploit.Education – Software exploitation & binary exploitation training 14:07 - 24. Pentest Tools – Online penetration testing suite 14:38 - 25. MITRE ATT&CK Framework – Understanding adversary tactics and techniques 15:06 - Conclusion