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Linux Interview Questions

Are Linux commands case sensitive (easy red flag question)?

Yes

Location of system logs

/var/log/messages

Command to view boot logs?

dmesg

Can you legally edit the Linux kernel code?

It is open source software under GPL2. Anyone can edit and make changes.

Where is swap space located and what is it used for?

It is located in a dedicated swap partition. It is used to extend the available memory to start new processes, by storing infrequently used pages there.

What is the difference between memory buffers and cache?

Buffers remember what's in directories, what file permissions are, and keep track of what memory is being written from or read to for a particular block device. The cache only contains the contents of the files themselves.

Hard Links * Points to another file's inode directly (the physical location) * Acts like an additional name to the same file * Cannot be used across file systems.

Soft Links - Points to another filename - if original filename is deleted, softlink becomes broken - Can be used across file names

You see the load average of a system and the numbers are 0.5 1 2. What does this mean?

For the past minute, 0.5 processes were waiting for the cpu. In the past minutes, an average of one process was waiting. For the past 15, an average of 2 processes were waiting.

What is the first process that is started by the kernel in Linux and what is its process id?

The first process started by the kernel in Linux is “init” and its process id is 1.

A large file is taking up all the space on a partition. You delete it, yet the partition is still full. Why?

There is a process holding the file handle open. It needs to be stopped before the space can be freed.

What command can you use to show which process is holding the file open?

lsof

What types of files/directories start with '.'?

Hidden

What is the pwd command?

Shows current path

What are the three permissions under Linux?

Read, Write, Execute

How are the three permissions applied on the system?

User, Group, Everyone/Other/All

What command is used to set permissions?

chmod

What is the purpose of a sticky bit?

Prevents anyone who is not the owner, owning group or root from removing or renaming a file

What command do you use to change file/directory ownership?

chown

Should you use telnet to administrate a Linux server? No, it is not encrypted.

Differences between Cron and Anacron?

  • A Cron job can be scheduled by any normal user, while Anacron can be scheduled only by a superuser
  • Cron expects the system to be up and running, while Anacron doesn’t expect this all the time. In the case of Anacron, if a job is scheduled and the system is down at this time, it will execute the job as soon as the system is up and running.
  • Cron is ideal for servers, Anacron is ideal for both desktops and laptops.
  • Cron should be used when we want a job to be executed at a particular hour and minute, while Anacron should be used when the job can be executed at any time.

What is a Zombie process?

It's a dead or finished process that still has an entry in the process table. It's parent hasn't read the exit status.

What commands do you run to kill a process?

ps and kill. Maybe some sudo if you don't have the rights.

Tell me about the /proc file system

The /proc file system is a RAM based file system which maintains information about the current state of the running kernel including details on CPU, memory, partitioning, interrupts, I/O addresses, DMA channels, and running processes. This file system is represented by various files which do not actually store the information, they point to the information in the memory. The /proc file system is maintained automatically by the system

Explain key based authentication (more details the better) - The generation of private/public air ssh-keygen - Which key is transferred to the remote host (public) via ssh-copy-id (or manually) - The file where public keys are stored authorized_keys - Proper permissions for authorized_keys chmod 600 ~/.ssh/authorized_keys

What does lspci do?

The lspci command displays information about PCI buses and the devices attached to your system

What are the different types of modes in VI editor?

  • Command Mode - from Escape
  • Insert/Edit Mode - from 'i'
  • Execution/Replacement - from ':'

Name the four Configuration Management Tools used in UNIX-like operating systems.

  • Ansible
  • Chef
  • Puppet
  • CFEngine