Linux Questions | PrepOps.Dev

Linux 101 17 questions

#1
What is Linux?
#2
Explain what each of the following commands does and give an example on how to use it:
- touch
  - ls
  - rm
  - cat
  - cp
  - mkdir
  - pwd
  - cd
#3
What each of the following commands does?
- cd /
  - cd ~
  - cd
  - cd ..
  - cd .
  - cd -
#4
Some of the commands in the previous question can be run with the -r/-R flag. What does it do? Give an example to when you would use it
#5
Explain each field in the output of ls -l command
#6
What are hidden files/directories? How to list them?
#7
What do > and < do in terms of input and output for programs?
#8
Explain what each of the following commands does and give an example on how to use it:
- sed
  - grep
  - cut
  - awk
#9
How to rename the name of a file or a directory?
#10
Specify which command would you use (and how) for each of the following scenarios
- Remove a directory with files
  - Display the content of a file
  - Provides access to the file /tmp/x for everyone
  - Change working directory to user home directory
  - Replace every occurrence of the word "good" with "great" in the file /tmp/y
#11
How can you check what is the path of a certain command?
#12
What is the difference between these two commands? Will it result in the same output?
```
echo hello world
echo "hello world"
```
#13
Explain piping. How do you perform piping?
#14
Fix the following commands:
- sed "s/1/2/g' /tmp/myFile
  - find . -iname *.yaml -exec sed -i "s/1/2/g" {} ;
#15
How to check which commands you executed in the past?
#16
Running the command df you get "command not found". What could be wrong and how to fix it?
#17
How do you schedule tasks periodically?

I/O Redirection 5 questions

#18
Explain Linux I/O redirection
#19
Demonstrate Linux output redirection
#20
Demonstrate Linux stderr output redirection
#21
Demonstrate Linux stderr to stdout redirection
#22
What is the result of running the following command? yippiekaiyay 1>&2 die_hard

Filesystem Hierarchy Standard 8 questions

#23
In Linux FHS (Filesystem Hierarchy Standard) what is the /?
#24
What is stored in each of the following paths?
- /bin, /sbin, /usr/bin and /usr/sbin
  - /etc
  - /home
  - /var
  - /tmp
#25
What is special about the /tmp directory when compared to other directories?
#26
What kind of information one can find in /proc?
#27
What makes /proc different from other filesystems?
#28
True or False? only root can create files in /proc
#29
What can be found in /proc/cmdline?
#30
In which path can you find the system devices (e.g. block storage)?

Permissions 11 questions

#31
How to change the permissions of a file?
#32
What does the following permissions mean?:
- 777
  - 644
  - 750
#33
What this command does? chmod +x some_file
#34
Explain what is setgid and setuid
#35
What is the purpose of sticky bit?
#36
What the following commands do?
- chmod
  - chown
  - chgrp
#37
What is sudo? How do you set it up?
#38
True or False? In order to install packages on the system one must be the root user or use the sudo command
#39
Explain what are ACLs. For what use cases would you recommend to use them?
#40
You try to create a file but it fails. Name at least three different reason as to why it could happen
#41
A user accidentally executed the following chmod -x $(which chmod). How to fix it?

Scenarios 3 questions

#42
You would like to copy a file to a remote Linux host. How would you do?
#43
How to generate a random string?
#44
How to generate a random string of 7 characters?

Systemd 5 questions

#45
What is systemd?
#46
How to start or stop a service?
#47
How to check the status of a service?
#48
On a system which uses systemd, how would you display the logs?
#49
Describe how to make a certain process/app a service

Troubleshooting and Debugging 12 questions

#50
Where system logs are located?
#51
How to follow file's content as it being appended without opening the file every time?
#52
What are you using for troubleshooting and debugging network issues?
#53
What are you using for troubleshooting and debugging disk & file system issues?
#54
What are you using for troubleshooting and debugging process issues?
#55
What are you using for debugging CPU related issues?
#56
You get a call from someone claiming "my system is SLOW". What do you do?
#57
Explain iostat output
#58
How to debug binaries?
#59
What is the difference between CPU load and utilization?
#60
How you measure time execution of a program?
#61
You have a process writing to a file. You don't know which process exactly, you just know the path of the file. You would like to kill the process as it's no longer needed. How would you achieve it?

Kernel 13 questions

#62
What is a kernel, and what does it do?
#63
How do you find out which Kernel version your system is using?
#64
What is a Linux kernel module and how do you load a new module?
#65
Explain user space vs. kernel space
#66
In what phases of kernel lifecycle, can you change its configuration?
#67
Where can you find kernel's configuration?
#68
Where can you find the file that contains the command passed to the boot loader to run the kernel?
#69
How to list kernel's runtime parameters?
#70
Will running sysctl -a as a regular user vs. root, produce different result?
#71
You would like to enable IPv4 forwarding in the kernel, how would you do it?
#72
How sysctl applies the changes to kernel's runtime parameters the moment you run sysctl command?
#73
How changes to kernel runtime parameters persist? (applied even after reboot to the system for example)
#74
Are the changes you make to kernel parameters in a container, affects also the kernel parameters of the host on which the container runs?

SSH 7 questions

#75
What is SSH? How to check if a Linux server is running SSH?
#76
Why SSH is considered better than telnet?
#77
What is stored in ~/.ssh/known_hosts?
#78
You try to ssh to a server and you get "Host key verification failed". What does it mean?
#79
What is the difference between SSH and SSL?
#80
What ssh-keygen is used for?
#81
What is SSH port forwarding?

Globbing & Wildcards 11 questions

#82
What is Globbing?
#83
What are wildcards? Can you give an example of how to use them?
#84
Explain what will ls [XYZ] match
#85
Explain what will ls [^XYZ] match
#86
Explain what will ls [0-5] match
#87
What each of the following matches
- ?
#88
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
#89
Which line numbers will be printed when running grep '\baaa\b' on the following content:
aaa bbb ccc.aaa aaaaaa
#90
What is the difference single and double quotes?
#91
What is escaping? What escape character is used for escaping?
#92
What is an exit code? What exit codes are you familiar with?

Boot Process 4 questions

#93
Tell me everything you know about the Linux boot process
#94
What is GRUB2?
#95
What is Secure Boot?
#96
What can you find in /boot?

Disk and Filesystem 23 questions

#97
What's an inode?
#98
Which of the following is not included in inode:
- Link count
  - File size
  - File name
  - File timestamp
#99
How to check which disks are currently mounted?
#100
You run the mount command but you get no output. How would you check what mounts you have on your system?
#101
What is the difference between a soft link and hard link?
#102
True or False? You can create an hard link for a directory
#103
True or False? You can create a soft link between different filesystems
#104
True or False? Directories always have by minimum 2 links
#105
What happens when you delete the original file in case of soft link and hard link?
#106
Can you check what type of filesystem is used in /home?
#107
What is a swap partition? What is it used for?
#108
How to create a
- new empty file
  - a file with text (without using text editor)
  - a file with given size
#109
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?
#110
How would you check what is the size of a certain directory?
#111
What is LVM?
#112
Explain the following in regards to LVM:
- PV
  - VG
  - LV
#113
What is NFS? What is it used for?
#114
What RAID is used for? Can you explain the differences between RAID 0, 1, 5 and 10?
#115
Describe the process of extending a filesystem disk space
#116
What is lazy umount?
#117
What is tmpfs?
#118
What is stored in each of the following logs?
- /var/log/messages
  - /var/log/boot.log
#119
True or False? both /tmp and /var/tmp cleared upon system boot

Performance Analysis 6 questions

#120
How to check what is the current load average?
#121
You know how to see the load average, great. but what each part of it means? for example 1.43, 2.34, 2.78
#122
How to check process usage?
#123
How to check disk I/O?
#124
How to check how much free memory a system has? How to check memory consumption by each process?
#125
How to check TCP stats?

Processes 27 questions

#126
how to list all the processes running in your system?
#127
How to run a process in the background and why to do that in the first place?
#128
How can you find how much memory a specific process consumes?
#129
What signal is used by default when you run 'kill process id'?
#130
What signals are you familiar with?
#131
What kill 0 does?
#132
What kill -0 does?
#133
What is a trap?
#134
Every couple of days, a certain process stops running. How can you look into why it's happening?
#135
What happens when you press ctrl + c?
#136
What is a Daemon in Linux?
#137
What are the possible states of a process in Linux?
#138
How do you kill a process in D state?
#139
What is a zombie process?
#140
How to get rid of zombie processes?
#141
How to find all the
- Processes executed/owned by a certain user
  - Process which are Java processes
  - Zombie Processes
#142
What is the init process?
#143
Can you describe how processes are being created?
#144
How to change the priority of a process? Why would you want to do that?
#145
Can you explain how network process/connection is established and how it's terminated?>
#146
What strace does? What about ltrace?
#147
Find all the files which end with '.yml' and replace the number 1 in 2 in each file
#148
You run ls and you get "/lib/ld-linux-armhf.so.3 no such file or directory". What is the problem?
#149
How would you split a 50 lines file into 2 files of 25 lines each?
#150
What is a file descriptor? What file descriptors are you familiar with?
#151
What is NTP? What is it used for?
#152
Explain Kernel OOM

Security 9 questions

#153
What is chroot? In what scenarios would you consider using it?
#154
What is SELiunx?
#155
What is Kerberos?
#156
What is nftables?
#157
What firewalld daemon is responsible for?
#158
Do you have experience with hardening servers? Can you describe the process?
#159
How do you create a private key for a CA (certificate authority)?
#160
How do you create a public key for a CA (certificate authority)?
#161
Demonstrate one way to encode and decode data in Linux

Networking 18 questions

#162
How to list all the interfaces?
#163
What is the loopback (lo) interface?
#164
What the following commands are used for?
- ip addr
  - ip route
  - ip link
  - ping
  - netstat
  - traceroute
#165
What is a network namespace? What is it used for?
#166
How to check if a certain port is being used?
#167
How can you turn your Linux server into a router?
#168
What is a virtual IP? In what situation would you use it?
#169
True or False? The MAC address of an interface is assigned/set by the OS
#170
Can you have more than one default gateway in a given system?
#171
What is telnet and why is it a bad idea to use it in production? (or at all)
#172
What is the routing table? How do you view it?
#173
How can you send an HTTP request from your shell?
#174
What are packet sniffers? Have you used one in the past? If yes, which packet sniffers have you used and for what purpose?
#175
How to list active connections?
#176
How to trigger neighbor discovery in IPv6?
#177
What is network interface bonding and do you know how it's performed in Linux?
#178
What network bonding modes are there?
#179
What is a bridge? How it's added in Linux OS?

DNS 5 questions

#180
How to check what is the hostname of the system?
#181
What the file /etc/resolv.conf is used for? What does it include?
#182
What commands are you using for performing DNS queries (or troubleshoot DNS related issues)?
#183
You run dig codingshell.com and get the following result:
```
ANSWER SECTION:
codingshell.com.	3515	IN	A	185.199.109.153
```
What is the meaning of the number 3515?
#184
How can we modify the network connection via nmcli command, to use 8.8.8.8 as a DNS server?

Packaging 9 questions

#185
Do you have experience with packaging? (as in building packages) Can you explain how does it works?
#186
How packages installation/removal is performed on the distribution you are using?
#187
RPM: explain the spec format (what it should and can include)
#188
How do you list the content of a package without actually installing it?
#189
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?
#190
Where repositories are stored? (based on the distribution you are using)
#191
What is an archive? How do you create one in Linux?
#192
How to extract the content of an archive?
#193
Why do we need package managers? Why not simply creating archives and publish them?

DNF 2 questions

#194
What is DNF?
#195
How to look for a package that provides the command /usr/bin/git? (the package isn't necessarily installed)

Applications and Services 6 questions

#196
What can you find in /etc/services?
#197
How to make sure a Service starts automatically after a reboot or crash?
#198
You run ssh 127.0.0.1 but it fails with "connection refused". What could be the problem?
#199
How to print the shared libraries required by a certain program? What is it useful for?
#200
What is CUPS?
#201
What types of web servers are you familiar with?

Users and Groups 15 questions

#202
What is a "superuser" (or root user)? How is it different from regular users?
#203
How do you create users? Where user information is stored?
#204
Which file stores information about groups?
#205
How do you change/set the password of a user?
#206
Which file stores users passwords? Is it visible for everyone?
#207
Do you know how to create a new user without using adduser/useradd command?
#208
What information is stored in /etc/passwd? explain each field
#209
How to add a new user to the system without providing him the ability to log-in into the system?
#210
How to switch to another user? How to switch to the root user?
#211
What is the UID the root user? What about a regular user?
#212
What can you do if you lost/forogt the root password?
#213
What is /etc/skel?
#214
How to see a list of who logged-in to the system?
#215
Explain what each of the following commands does:
- useradd
  - usermod
  - whoami
  - id
#216
You run grep $(whoami) /etc/passwd but the output is empty. What might be a possible reason for that?

Hardware 4 questions

#217
Where can you find information on the processor (like number of CPUs)?
#218
How can you print information on the BIOS, motherboard, processor and RAM?
#219
How can you print all the information on connected block devices in your system?
#220
True or False? In user space, applications don't have full access to hardware resources

Namespaces 7 questions

#221
What types of namespaces are there in Linux?
#222
True or False? In every PID (Process ID) namespace the first process assigned with the process id number 1
#223
True or False? In a child PID namespace all processes are aware of parent PID namespace and processes and the parent PID namespace has no visibility of child PID namespace processes
#224
True or False? By default, when creating two separate network namespaces, a ping from one namespace to another will work fine
#225
True or False? With UTS namespaces, processes may appear as if they run on different hosts and domains while running on the same host
#226
True or False? It's not possible to have a root user with ID 0 in child user namespaces
#227
What time namespaces are used for?

Virtualization 3 questions

#228
What virtualization solutions are available for Linux?
#229
What is KVM?
#230
What is Libvirt?

AWK 6 questions

#231
What the awk command does? Have you used it? What for?
#232
How to print the 4th column in a file?
#233
How to print every line that is longer than 79 characters?
#234
What the lsof command does? Have you used it? What for?
#235
What is the difference between find and locate?
#236
How a user process performs a privileged operation, such as reading from the disk?

System Calls 22 questions

#237
What is a system call? What system calls are you familiar with?
#238
How a program executes a system call?
#239
Explain the fork() system call
#240
What is the return value of fork()?
#241
Name one reason for fork() to fail
#242
Why do we need the wait() system call?
#243
How the kernel notifies the parent process about child process termination?
#244
How the waitpid() is different from wait()?
#245
True or False? The wait() system call won't return until the child process has run and exited
#246
Explain the exec() system call
#247
True or False? A successful call to exec() never returns
#248
What system call is used for listing files?
#249
What system calls are used for creating a new process?
#250
What execve() does?
#251
What is the return value of malloc?
#252
Explain the pipe() system call. What does it used for?
#253
What happens when you execute ls -l?
#254
What happens when you execute ls -l *.log?
#255
What readdir() system call does?
#256
What exactly the command alias x=y does?
#257
Why running a new program is done using the fork() and exec() system calls? why a different API wasn't developed where there is one call to run a new program?
#258
Describe shortly what happens when you execute a command in the shell

Filesystem & Files 6 questions

#259
How to create a file of a certain size?
#260
What does the following block do?:
```
open("/my/file") = 5
read(5, "file content")
```
#261
Describe three different ways to remove a file (or its content)
#262
What is the difference between a process and a thread?
#263
What is context switch?
#264
You found there is a server with high CPU load but you didn't find a process with high CPU. How is that possible?

Advanced Networking 10 questions

#265
When you run ip a you see there is a device called 'lo'. What is it and why do we need it?
#266
What the traceroute command does? How does it works?
#267
What is network bonding? What types are you familiar with?
#268
How to link two separate network namespaces so you can ping an interface on one namespace from the second one?
#269
What are cgroups?
#270
Explain Process Descriptor and Task Structure
#271
What are the differences between threads and processes?
#272
Explain Kernel Threads
#273
What happens when socket system call is used?
#274
You executed a script and while still running, it got accidentally removed. Is it possible to restore the script while it's still running?

Memory 3 questions

#275
What is the difference between MemFree and MemAvailable in /proc/meminfo?
#276
What is the difference between paging and swapping?
#277
Explain what is OOM killer

Distributions 3 questions

#278
What is a Linux distribution?
#279
What Linux distributions are you familiar with?
#280
What are the components of a Linux distribution?

Sed 1 question

#281
Using sed, extract the date from the following line: 201.7.19.90 - - [05/Jun/1985:13:42:99 +0000] "GET /site HTTP/1.1" 200 32421

Misc 17 questions

#282
What is a Linux distribution?
#283
Name 5 commands which are two letters long
#284
What ways are there for creating a new empty file?
#285
How cd - works? How does it knows the previous location?
#286
List three ways to print all the files in the current directory
#287
How to count the number of lines in a file? What about words?
#288
You define x=2 in /etc/bashrc and x=6 ~/.bashrc you then login to the system. What would be the value of x?
#289
What is the difference between man and info?
#290
Explain "environment variables". How do you list all environment variables?
#291
What is a TTY device?
#292
How to create your own environment variables?
#293
What a double dash (--) mean?
#294
Wildcards are implemented on user or kernel space?
#295
If I plug a new device into a Linux machine, where on the system, a new device entry/file will be created?
#296
Why there are different sections in man? What is the difference between the sections?
#297
What is User-mode Linux?
#298
Under which license Linux is distributed?