Devops/SRE interview preparation questions

https://www.thegeekstuff.com/2011/02/linux-boot-process/

Explanation: https://linux-audit.com/understanding-memory-information-on-linux-systems/

* https://en.wikipedia.org/wiki/Sticky_bit * https://www.geeksforgeeks.org/setuid-setgid-and-sticky-bits-in-linux-file-permissions/

* https://serverfault.com/questions/138427/what-does-virtual-memory-size-in-top-mean * https://elinux.org/images/4/4c/Ott.pdf

Explanation: https://itsfoss.com/create-swap-file-linux/

* https://en.wikipedia.org/wiki/Zombie_process * https://www.geeksforgeeks.org/zombie-processes-prevention/ * https://stackoverflow.com/questions/16944886/how-to-kill-zombie-process

http://man7.org/linux/man-pages/man5/proc.5.html https://docs.kernel.org/filesystems/proc.html

https://www.maketecheasier.com/linux-top-explained/

https://medium.com/@307/hard-links-and-symbolic-links-a-comparison-7f2b56864cdd

* In most cases you will get unbootable system * https://askubuntu.com/questions/962660/what-happens-if-you-delete-the-root-user

https://www.howtogeek.com/441534/how-to-use-the-chroot-command-on-linux/

* https://dev.to/rrampage/surviving-the-linux-oom-killer-2ki9 * https://www.percona.com/blog/2019/08/02/out-of-memory-killer-or-savior/

* https://www.linuxjournal.com/content/oops-debugging-kernel-panics-0 * http://www.linuxandubuntu.com/home/things-to-know-about-linux-kernel-panic

https://www.computerhope.com/unix/unohup.htm

See filesystem /proc and find ID proccess in that directory should be script

https://en.wikipedia.org/wiki/StandardRAIDlevels

The file will be deleted if you delete only the last hardlink to this file.

cp /bin/cp /tmp/chmod   cp /bin/chmod /tmp/chmod   ./tmp/chmod 755 /bin/chmod

perl -e 'chmod(0755, "chmod")</code></pre>

Solution3:   <pre><code class="lang-">/lib/ld-linux.so.2 /bin/chmod 755 /bin/chmod</code></pre>
</b></details>
<details> <summary>What is Load Average?</summary><br><b> Explanation:
http://www.brendangregg.com/blog/2017-08-08/linux-load-averages.html </b></details>
<details> <summary>What are cgroups?</summary><br><b> Explanation:
https://www.linuxjournal.com/content/everything-you-need-know-about-linux-containers-part-i-linux-control-groups-and-process </b></details>
Networking and Security
<details> <summary>What is NAT?</summary><br><b> Explanation:
* https://www.geeksforgeeks.org/network-address-translation-nat/   * https://www.comptia.org/content/guides/what-is-network-address-translation </b></details>
<details> <summary>What is VLAN?</summary><br><b> Explanation:
https://study-ccna.com/what-is-a-vlan/ </b></details>
<details> <summary>What is ARP?</summary><br><b> Explanation:
Address Resolution Protocol.   https://en.wikipedia.org/wiki/AddressResolutionProtocol </b></details>
<details> <summary> How many layers are there under TCP/IP? Compare OSI and TCP/IP</summary><br><b> Explanation:
https://techdifferences.com/difference-between-tcp-ip-and-osi-model.html </b></details>
<details> <summary>Explain TCP 3-way handshake process</summary><br><b> Explanation:
https://www.geeksforgeeks.org/tcp-3-way-handshake-process/ </b></details>
<details> <summary>What is SSH and how does it work?</summary><br><b> Explanation:
https://www.ssh.com/ssh/command </b></details>
<details> <summary>Explain DNS records: SOA, PTR, A, MX, and CNAME</summary><br><b> Explanation:
https://www.presslabs.com/how-to/dns-records/ </b></details>
<details> <summary>How to check route table in Linux?</summary><br><b> Explanation:
netstat -rn

route -n

ip route list </b></details>

<details> <summary>Server1 can't reach to Server2. Describe possible reasons</summary><br><b> Explanation:
* Application layer:     Check if servers are correctly configured and services up and running   * Transport layer:     Check ports, check ping from server to server   * Network layer:     Check firewall and networking setting. Also check routes, dns and ARP tables. </b></details>
<details> <summary>How to check all of open ports on server?</summary><br><b> Explanation:
* nmap - if you need check all ports for remote server   * netstat - for localhost </b></details>

Programming
BASH
<details> <summary>How to check if the last command was run successfully?</summary><br><b> Explanation:
echo $? if returns 0 that last command executed successfully

</b></details>
<details> <summary>What is function? How to write a function?</summary><br><b> Explanation:
https://linuxize.com/post/bash-functions/ </b></details>
<details> <summary>Loops in BASH</summary><br><b> Explanation:
https://www.tldp.org/HOWTO/Bash-Prog-Intro-HOWTO-7.html </b></details>
<details> <summary> How would you compare two strings in a bash script?</summary><br><b> Explanation:   Case1:
<pre><code class="lang-">#!/bin/bash
VAR1=&quot;string1&quot; VAR2=&quot;string333&quot;
if [ &quot;$VAR1&quot; = &quot;$VAR2&quot; ]; then     echo &quot;Strings are equal.&quot; else     echo &quot;Strings are not equal.&quot; fi</code></pre>   Case2:
<pre><code class="lang-">[[ &quot;string1&quot; == &quot;string2&quot; ]] &amp;&amp; echo &quot;Equal&quot; || echo &quot;Not equal&quot;</code></pre>
</b></details>
<details> <summary> How to print all array elements and their indexes?</summary><br><b> Explanation:
<pre><code class="lang-">#!/bin/bash   array=(&quot;A&quot; &quot;B&quot; &quot;C&quot; &quot;X&quot; )   echo ${array[0]}</code></pre>
</b></details>
<details> <summary>Print number from 1 to 10 using for loop</summary><br><b> Explanation:
<pre><code class="lang-">#!/bin/bash   for i in {1..10}; do       echo $i   done</code></pre>
</b></details>
<details> <summary>How to debug a shell script ?</summary><br><b> Explanation:
Option -x   or -nv </b></details>

Python
<details>
<summary>Python for sysadmins</summary><br><b>
Explanation:
* https://realpython.com/   * https://python-for-system-administrators.readthedocs.io/en/latest/ </b></details>
<details> <summary>How to compile python application?</summary><br><b> Explanation:
There are two ways could go about to solve that problem:
Use a static builder, like freeze, or pyinstaller, or py2exe
Compile using cython
</b></details>
<details> <summary>What is PEP 8 and why is it important?</summary><br><b> Explanation:
* https://realpython.com/python-pep8/
</b></details>
Databases
<details> <summary>What is SQL?</summary><br><b> Explanation:   * http://www.sqlcourse.com/intro.html </b></details>
<details> <summary>SQL vs NoSQL. Explain benefits of both</summary><br><b> Explanation:
* https://www.youtube.com/watch?v=ZS_kXvOeQ5Y   * https://www.geeksforgeeks.org/difference-between-sql-and-nosql/ </b></details>
<details> <summary>What are tables and field?</summary><br><b> Explanation:
* https://intellipaat.com/blog/tutorial/sql-tutorial/tables-in-sql/ </b></details>
<details> <summary>What is an index?</summary><br><b> Explanation:   * https://www.tutorialspoint.com/sql/sql-indexes.htm </b></details>
<details> <summary>What is primary key?</summary><br><b> Explanation:   * https://www.w3schools.com/sql/sql_primarykey.ASP </b></details>
<details> <summary>What is database replication?</summary><br><b> Explanation:
* https://www.geeksforgeeks.org/data-replication-in-dbms/ </b></details>
<details> <summary>What is DynamoDB?</summary><br><b> Explanation:
* https://www.dynamodbguide.com/what-is-dynamo-db/ </b></details>
Version Control System (GIT)
<details> <summary>What is GIT?</summary><br><b> Explanation:
* https://git-scm.com/book/en/v2/Getting-Started-What-is-Git
</b></details>
<details> <summary> What are the benefits of using GIT?</summary><br><b> Explanation:
* Documentation   * Markdown   * Fully Distributed   * Simplicity   * Branching model   * open source
</b></details>
<details> <summary>What is the difference between git pull and git fetch ?</summary><br><b> Explanation:

* https://guide.freecodecamp.org/miscellaneous/git-pull-vs-git-fetch/
</b></details>
<details> <summary>What is the difference between git reset and git revert ?</summary><br><b> Explanation:

* https://stackoverflow.com/questions/8358035/whats-the-difference-between-git-revert-checkout-and-reset
</b></details>
<details> <summary>What is git rebase ?</summary><br><b> Explanation:

* https://www.atlassian.com/git/tutorials/rewriting-history/git-rebase
</b></details>
<details> <summary>How to reset last commit?</summary><br><b> Explanation:
* git reset --hard HEAD~1 - not a true way cuz you will lost all changes  * git revert ` - good way
for more https://stackoverflow.com/questions/927358/how-do-i-undo-the-most-recent-local-commits-in-git