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Linux Commands 2

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How to check Memory stats and CPU stats as a Linux admin?

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How to reduce or shrink the size of LVM partition?

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How can you enhance the security of password file?

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What is the difference between Cron and Anacron?

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What command is used to check the number of files, disk space and each user’s defined quota?

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How can you manage memory in linux machines?

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What is the name and path of the main system log?

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How to manage logical volumes?

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Explain /proc filesystem?

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What are the fields in the/etc/passwd file?

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How do you terminate an ongoing process?

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How can you know the execution time of a command?

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How can you append one file to another in Linux?

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How you can run a Linux program in the background simultaneously when you start your Linux Server?

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Difference in soft link and hard link?

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How to find a particular word from a file?

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What is stop command?

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How to stop particular process using Linux command?

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Can we delete content in a file by using SED command? How to do?

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How to rename the name of a file or a directory?

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Using mv command

What is stored in each of the following paths?

/bin, /sbin, /usr/bin and /usr/sbin

/etc

/home

/var

/tmp

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What is special about /tmp directory when compared to other directories?

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Explain each field in the output of `ls -l` command

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It shows a detailed list of files in a long format. From the left:

file permissions, number of links, owner name, owner group, file size, timestamp of last modification and directory/file name

What are hidden files/directories? How to list them?

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Explain piping. How do you perform piping?

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Running the command df you get "command not found". What could be wrong and how to fix it?

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How do you schedule tasks periodically?

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How to check which commands you executed in the past?

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How to change the permissions of a file?

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What does the following permissions mean?:

777

644

750

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What this command does? chmod +x Bhaskar.txt

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Explain what is setgid and setuid?

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What is the purpose of sticky bit?

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What the following commands do?

chmod

chown

chgrp

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You try to delete a file but it fails. Name at least three different reason as to why it could happen

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What is systemd?

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On a system which uses systemd, how would you display the logs?

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Describe how to make a certain process/app a service

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Where system logs are located?

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How to follow file's content as it being appended without opening the file every time?

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What are you using for troubleshooting and debugging network issues?

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What are you using for troubleshooting and debugging disk & file system issues?

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What are you using for troubleshooting and debugging process issues?

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What are you using for debugging CPU related issues?

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Explain iostat output

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How to debug binaries?

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What kind of information one can find in /proc?

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Can you create files in /proc?

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What is the difference between CPU load and utilization?

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How you measure time execution of a program?

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What is a kernel, and what does it do?

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How do you find out which Kernel version your system is using?

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What is a Linux kernel module and how do you load a new module?

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Explain user space vs. kernel space

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What are system calls? What system calls are you familiar with?

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What virtualization solutions are available for Linux?

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What is KVM?

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What is SSH? How to check if a Linux server is running SSH?

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Why SSH is considered better than telnet?

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What is stored in ~/.ssh/known_hosts?

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You try to ssh to a server and you get "Host key verification failed". What does it mean?

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What is the difference between SSH and SSL?

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What ssh-keygen is used for?

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What is SSH port forwarding?

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What is Globbing?

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What are wildcards? Can you give an example of how to use them?

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Explain what will ls [XYZ] match

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Explain what will ls [^XYZ] match

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Explain what will ls [0-5] match

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What each of the following matches

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What do we grep for in each of the following commands?:

grep '[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}' some_file

grep -E "error|failure" some_file

grep '[0-9]$' some_file

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Which line numbers will be printed when running `grep '\baaa\b'` on the following content:

aaa bbb ccc.aaa aaaaaa

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What is the difference single and double quotes?

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What is escaping? What escape character is used for escaping?

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What is an exit code? What exit codes are you familiar with?

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Tell me everything you know about the Linux boot process

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What is GRUB2?

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What is Secure Boot?

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What can you find in /boot?

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How to check which disks are currently mounted?

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You run mount command but you get no output. How would you check what mounts you have on your system?

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What is the difference between a soft link and hard link?

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True or False? You can create an hard link for a directory

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True or False? You can create a soft link between different filesystems

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What happens when you delete the original file in case of soft link and hard link?

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Can you check what type of filesystem is used in /home?

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What is a swap partition? What is it used for?

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How to create a * new empty file * a file with text (without using text editor) * a file with given size

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You are trying to create a new file but you get "File system is full". You check with df for free space and you see you used only 20% of the space. What could be the problem?

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How would you check what is the size of a certain directory?

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What do you know about LVM?

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Explain the following in regards to LVM:

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What is NFS? What is it used for?

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What RAID is used for? Can you explain the differences between RAID 0, 1, 5 and 10?

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Describe the process of extending a filesystem disk space

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What is lazy umount?

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What is tmpfs?

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Idenfy the wrong in below commands?

sed "s/1/2/g' /tmp/myFile

find . -iname *.yaml -exec sed -i "s/1/2/g" {} ;

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What is stored in each of the following logs?

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True or False? both /tmp and /var/tmp cleared upon system boot

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How to check what is the current load average?

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You know how to see the load average, great. but what each part of it means? for example 1.43, 2.34, 2.78

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How to check process usage?

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How to check disk I/O?

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How to check how much free memory a system has? How to check memory consumption by each process?

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How to check TCP stats?

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How to list all the processes running in your system?

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How to run a process in the background and why to do that in the first place?

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How can you find how much memory a specific process consumes?

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What signal is used by default when you run 'kill *process id*'?

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What signals are you familiar with?

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What kill 0 does?

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What kill -0 does?

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What is a trap?

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Every couple of days, a certain process stops running. How can you look into why it's happening?

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What happens when you press ctrl + c?

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What is a Daemon in Linux?

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What are the possible states of a process in Linux?

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How do you kill a process in D state?

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What is a zombie process?

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How to get rid of zombie processes?

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How to find all the

Processes executed/owned by a certain user

Process which are Java processes

Zombie Processes

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What is the init process?

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How to change the priority of a process? Why would you want to do that?

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Can you explain how network process/connection is established and how it's terminated?

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What strace does? What about ltrace?

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Find all the files which end with '.yml' and replace the number 1 in 2 in each file

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You run ls and you get "/lib/ld-linux-armhf.so.3 no such file or directory". What is the problem?

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How would you split a 50 lines file into 2 files of 25 lines each?

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What is a file descriptor? What file descriptors are you familiar with?

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What is NTP? What is it used for?

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Explain Kernel OOM

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Linux Security

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What is chroot? In what scenarios would you consider using it?

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What is SELiunx?

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What is Kerberos?

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What is nftables?

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What firewalld daemon is responsible for?

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Do you have experience with hardening servers? Can you describe the process?

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Linux Networking

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How to list all the interfaces?

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What is the loopback (lo) interface?

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What the following commands are used for?

ip addr

ip route

ip link

ping

netstat

traceroute

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What is a network namespace? What is it used for?

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How to check if a certain port is being used?

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How can you turn your Linux server into a router?

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What is a virtual IP? In what situation would you use it?

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True or False? The MAC address of an interface is assigned/set by the OS

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Can you have more than one default gateway in a given system?

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Which port is used in each of the following protocols?:

SSH

SMTP

HTTP

DNS

HTTPS

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What is telnet and why is it a bad idea to use it in production? (or at all)

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What is the routing table? How do you view it?

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How can you send an HTTP request from your shell?

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What are packet sniffers? Have you used one in the past? If yes, which packet sniffers have you used and for what purpose?

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How to list active connections?

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How to trigger neighbor discovery in IPv6?

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What is network interface bonding and do you know how it's performed in Linux?

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What network bonding modes are there?

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What is a bridge? How it's added in Linux OS?

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How to check what is the hostname of the system?

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What the file /etc/resolv.conf is used for? What does it include?

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What commands are you using for performing DNS queries (or troubleshoot DNS related issues)?

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Do you have experience with packaging? (as in building packages) Can you explain how does it works?

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How packages installation/removal is performed on the distribution you are using?

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RPM: explain the spec format (what it should and can include)

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How do you list the content of a package without actually installing it?

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How to know to which package a file on the system belongs to? Is it a problem if it doesn't belongs to any package?

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Where repositories are stored? (based on the distribution you are using)

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What is an archive? How do you create one in Linux?

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How to extract the content of an archive?

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Why do we need package managers? Why not simply creating archives and publish them?

How to look for a package that provides the command /usr/bin/git? (the package isn't necessarily installed)

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Linux Applications and Services

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What can you find in /etc/services?

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How to make sure a Service starts automatically after a reboot or crash?

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You run ssh 127.0.0.1 but it fails with "connection refused". What could be the problem?

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How to print the shared libraries required by a certain program? What is it useful for?

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What is CUPS?

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What types of web servers are you familiar with?

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What is a "superuser" (or root user)? How is it different from regular users?

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How do you create users? Where user information is stored?

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Which file stores information about groups?

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How do you change/set the password of a user?

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Which file stores users passwords? Is it visible for everyone?

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Do you know how to create a new user without using adduser/useradd command?

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What information is stored in /etc/passwd? explain each field

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How to add a new user to the system without providing him the ability to log-in into the system?

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How to switch to another user? How to switch to the root user?

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What is the UID the root user? What about a regular user?

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What can you do if you lost/forogt the root password?

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What is sudo? How do you set it up?

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What is /etc/skel?

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How to see a list of who logged-in to the system?

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Explain what each of the following commands does:

useradd

usermod

whoami

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Where can you find information on the processor?

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How can you print information on the BIOS, motherboard, processor and RAM?

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How can you print all the information on connected block devices in your system?

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Give 5 commands which are two letters long

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What ways are there for creating a new empty file?

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How `cd -` works? How does it knows the previous location?

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List three ways to print all the files in the current directory

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How to count the number of lines in a file? What about words?

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You define x=2 in /etc/bashrc and x=6 ~/.bashrc you then login to the system. What would be the value of x?

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What is the difference between man and info?

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Explain "environment variables". How do you list all environment variables?

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How to create your own environment variables?

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What a double dash (--) mean?

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What the awk command does? Have you used it? What for?

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How to print the 4th column in a file?

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How to print every line that is longer than 79 characters?

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What the lsof command does? Have you used it? What for?

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What commands you can use for searching files and/or directories?

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How can you check what is the path of a certain command?

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Explain the fork() system call

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Explain the exec() system call

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What system call is used for listing files?

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What system call is used for creating a new process?

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What are the differences between exec() and fork()?

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Why do we need the wait system call?

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What execve() does?

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What is the return value of malloc?

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Explain the pipe() system call. What does it used for?

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What happens when you execute ls -l?

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What happens when you execute ls -l *.log?

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What readdir() system call does?

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What exactly the command alias x=y does?

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Linux Filesystem & Files

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How to create a file of a certain size?

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Can you describe how processes are being created?

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What does the following block do?:

open("/my/file") = 5

read(5, "file content")

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Describe three different ways to remove a file (or its content)

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What is the difference between a process and a thread?

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What is context switch?

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You found there is a server with high CPU load but you didn't find a process with high CPU. Ans)

How is that possible?

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When you run ip a you see there is a device called 'lo'. What is it and why do we need it?

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What the traceroute command does? How does it works?

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What is network bonding? What types are you familiar with?

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How to link two separate network namespaces so you can ping an interface on one namespace from the second one?

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What are cgroups?

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Explain Process Descriptor and Task Structure

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What are the differences between threads and processes?

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Explain Kernel Threads

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What happens when socket system call is used?

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You executed a script and while still running, it got accidentally removed. Is it possible to restore the script while it's still running?

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What is the difference between MemFree and MemAvailable in /proc/meminfo?

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What is virtual memory?

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What is the difference between paging and swapping?

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Explain what is OOM killer

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What is a Linux distribution?

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What Linux distributions are you familiar with?

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What are the components of a Linux distribution?

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Wildcards are implemented on user or kernel space?

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If I plug a new device into a Linux machine, where on the system, a new device entry/file will be created?

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Why there are different sections in man? What is the difference between the sections?

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