Linux administrator questions

Question

linux

I was asked to interview for the position of a linux administrator in a WEB company.
So I'm wondering what to ask?
Does anyone have any ideas on the topic? Please advise.
Thanks in advance!

Answer 1

There was a vacancy in the hosting company NetAngels. The list was as follows:
NetAngels is looking for a qualified technical person for the position of Senior System Administrator in the NOC department. In our work, we use Debian GNU/Linux, so we will be especially glad to specialists who have experience working with this particular distribution.
Tasks that you have to solve:
— support of the existing infrastructure of our hosting platform;
— research and implementation of new technical solutions;
— solving complex problems and issues that are beyond the competence of the technical support service.
Qualities that will be useful when working in our company:
- understanding of the functioning of linux-systems, experience in their administration;
— understanding of the principles of Internet functioning, familiarity with dns, http, ftp, smtp, pop3, imap protocols;
- some ideas about the C language (the need to look into the code of a program in the absence of intelligible documentation should not become an impossible task for you);
— experience in writing scripts in sh, mastery of sed and awk;
— technical English at the level of fluent reading of documentation (without constant looking into the dictionary);
- Responsibility and willingness to quickly make decisions on emerging problems;
- independence: research of opportunities for the implementation of technical innovations, the ability to choose the appropriate tool for solving a problem.
- understanding the linux network stack device and the netfilter kernel subsystem;
— experience with non-trivial iptables, iproute2 configurations;
- Familiarity with dynamic routing protocols;
- skills in working with Debian / Ubuntu distributions (package manager, experience in building packages);
- Experience with virtualization systems;
— skills in diagnosing and solving non-trivial problems in the field of network settings or the operation of services running on the linux platform;
— experience with high-load services operating 24/7/365;
- familiarity with Apache or nginx web servers;
- experience in setting up a mail system on the linux platform;
- familiarity with version control systems (preferably git);
- ideas about what a sql query plan is, the skills of optimizing any DBMS for a specific task;
- Python programming skills;
Well, the questions themselves:
1. How to find out which of the clients consumes more resident memory at the moment by their processes (build a top by consumption). The output of ps (not complete) looks like this. There are several hundreds of processes in ps:
Source:
ps axu
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
u5867 32518 0.0 0.0 214036 12764? S 21:34 0:00 /usr/bin/php-cgi5.2
u425 32532 1.1 0.0 139736 24556? S 21:34 0:01 /usr/bin/php-cgi5.3
u6363 32535 ​​1.1 0.0 183444 20240? S 21:34 0:01 /usr/bin/php-cgi5.2
u12124 32548 0.2 0.0 174432 28360? S 21:34 0:00 /usr/bin/php-cgi5.2
2. How does the traceroute program work?
3. You needed to allocate a subnet of 30 ip addresses. Can you mentally calculate what the mask of the resulting network should be?
4. Tell us what Path MTU is.
5. Explain what a TCP Window is.
6. What type of DNS record will we use when specifying which server is responsible for receiving mail from a particular domain?
7. What does an HTTP request look like to check the correct operation of the web server settings for serving compressed content when it is supported by the client (for example, /index.html)?
8. Tell us what are the differences between a symlink and a hardlink.
9. How can sh/bash handle any signal? For example, at the end of the script, it is necessary to delete temporary files created during the work, and this must be done even if the script execution was interrupted from the outside. What signals can we not process?
10. You need to ensure the maximum availability of one service (program). Tell us how you can ensure the automatic start / restart of the service in case of its out-of-band completion.
11. For the new server that will run the databases, you need to prepare the disk system. Please tell us how you will be guided when setting up disks, what raid settings will you use, what io scheduler?
12. How to see what parameters the linux kernel is running with?
13. Have you ever dealt with tun/tap devices? What is their difference?
14. Is it possible to completely disable swap on the server? Why?
15. How can I view disk I/O usage?
16. Two interfaces are configured on the server: eth0 and eth1. The default gateway is accessible via eth0. Requests arrive at the server through both interfaces. How can I configure the use of another gateway to send responses to requests that come through eth1? It is assumed that the request can come from an arbitrary ip-address.
17. How will you back up a 10 GB MySQL database using InnoDB storage? And if the storage is MyISAM?
18. What difficulties/problems have you encountered with MySQL replication support, if any? How did you fix the broken replication?
19. Suppose you have some kind of website running under LAMP. An http-flood attack has begun on this site. What actions would you take to deal with this attack on your own?
20. There is a certain large (several dozen) number of identical systems configured for one task (hosting). How will you work on installing new software, updating; monitor the relevance and uniformity of configuration files?
21. When is it advisable to use Jumbo Frames?
22. If you were given the task of building a failover cluster to run a website on LAMP, what technologies did you use to do this and why?
23. It is necessary to deny access to the sites hosted on the server to all clients with User-Agent: MegaXakep. How would you do it?
24. What is the difference between KVM, XEN and OpenVZ. What are the advantages and disadvantages of each of these technologies?
25. It is necessary to limit the processes of the user uXXXX so that they consume no more than 512 MB of memory in total. How can I do that?
26. What database change replication modes are supported by MySQL?
27. In what cases may it be necessary to keep binlog on slaves?
Taken here www.e1.ru/talk/forum/go_to_message.php?f=125&t=33520&i=33603

Answer 2

When I went to the interview, we talked about anime ... They took it.

Answer 3

Get a Linux machine. Break everything on it that your hands can reach, give it to the applicant for repair. See what and how he will do. Then ask what he did at his previous job and ... that's it. So I see the perfect interview for the position of linux administrator.

Answer 4

A very good option:
hydrobiont.livejournal.com/107182.html#cutid1
There is also this:
Question 1.
Please tell us about the types of packet filters, about the difference between stateful and
stateless behavior,
about Packet filters in various systems.
Question 2.
How to organize packet filter rulesets.
The machine with one external interface is given. Make groups of rules (in any
form, it is possible in free) for the following
conditions: open services: ftp, ssh, smtp, named, http. ftp must work
in both passive and active modes,
outgoing connections are allowed.
Question 3.
a) MySQL replication.
Database replication is configured on two servers. How to make sure that everything is in order with replication
?
What to do if replication "broke"?
b) There is a db base. It has 3 tables staff(id1, name), phone(id2, number),
office(id3, room).
How to make 1 query that outputs employees who are in
room 13
and their phone number starts with 13 in the format "name, phone, room".
Question 4.
Given tcp session. Explain the nature of this session.
What does she mean?
pastebin.com/LawY6C5D
Question 5. On a production server after an abnormal reboot, the
disk check fails and
you see a bad superblock message. Your actions?
Question 6.
Can you provide a small fragment of your Bash code describing how it works?
Question 7
Have you made changes to the existing code of other people's programs? Give,
please, an example (in the form of diff).
Question 8.
What are some ways to improve the performance of web applications?
Can apache serve 1000-2000 concurrent connections?
How can the load on the server be reduced in this case?
Question 9.
Virtualization.
a) What software implementations did you use in your work?
b) What is the fundamental difference between OpenVZ and KVM?
c) What fine adjustments, modifications were made when working with
virtualization systems to distinguish between the use of the disk subsystem?
d) Have you performed memory optimization in the KVM virtualization system? If yes, what technology did you use?
Question 10.
What software version control systems did you use in your work? What tools
for organizing teamwork did you use?

Answer 5

Give the console and ask to create a file if vi writes take.
It's a joke, of course, but there's some truth to it.
I know the case created a similar situation only on windows, the girl was hired because far launched.

Answer 6

Invite a couple of cool penguin admins and ask them to chat.
No other way.

Answer 7

1) Eddy_Em's idea at the very beginning is more than good. And here's what: in reality, it usually happens like this: at first everything was set up, everything works well, then bam, and something broke, and no one knows why. an adequate administrator should be able to solve such problems. and here is an honest emulation.
2) I also really liked the post from ASP, great selection, thanks for it!

Answer 8

Talk to no end. To immediately send stupid applicants - ask about DNS, there is also a good question "what happens from the moment the user clicks on the link in the browser until the moment he sees the page" and a bunch of similar ones.
Whoever likes the answers - read above how to interview further.