/linux-interview

Interview questions

Linux Administration interview questions

Simple Linux Questions:

  • What is the name and the UID of the administrator user?
  • How to list all files, including hidden one, in a directory?
  • What is the Unix/Linux command to remove a directory and its contents?
  • Which command will show you free/used memory? Does free memory exist on Linux?
  • How to connect to a remote server or what is SSH?
  • I get "command not found" for ifconfig -a. What can be wrong?
  • What command will show the available disk space on the Unix/Linux system?
  • What Unix/Linux commands will alter a files ownership, files permissions?
  • What does chmod +x FILENAMEdo?
  • What does the permission 0750 on a file mean?
  • What does the permission 0750 on a directory mean?
  • How to redirect STDOUT and STDERR in bash? (> /dev/null 2>&1)
  • What is the difference between UNIX and Linux
  • What is the difference between Telnet and SSH?
  • Explain the three load averages and what do they indicate

Medium Linux Questions:

  • What is a packet filter and how does it work?
  • What is swap and what is it used for?
  • What is an A record, an NS record, a PTR record, a CNAME record, an MX record?
  • Are there any other RRs and what are they used for?
  • What is the sticky bit?
  • What is an inode and what fields are stored in an inode?
  • What is a runlevel and how to get the current runlevel?
  • What is SSH port forwarding?
  • Describe a scenario when you get a "filesystem is full" error, but 'df' shows there is free space.
  • Describe a scenario when deleting a file, but 'df' not showing the space being freed.
  • What happens to a child process that dies and has no parent process to wait for it and what’s bad about this?
  • How to know which process listens on a specific port?
  • What is Iptables?
  • Which privilege is required to operate iptables?
  • How can you find all the regular files in a directory?
  • What is LVM?
  • Which command is used to extend a logical volume?
  • Tell me the steps to remove the swap file?
  • What is the role of /etc/resolv.conf file?
  • What daemon is responsible for tracking events on your system?

Hard Linux Questions:

  • What shortcuts do you use on a regular basis?
  • What kind of keys are in ~/.ssh/authorized_keys and what it is this file used for?
  • I've added my public ssh key into authorized_keys but I'm still getting a password prompt, what can be wrong?
  • Did you ever create RPM's, DEB's or solaris pkg's?
  • Describe the linux boot process with as much detail as possible, starting from when the system is powered on and ending when you get a prompt.
  • When trying to umount a directory it says it's busy, how to find out which PID holds the directory?
  • How do you debug a running process or a library that is being called? A: strace -p PID
  • What are the steps to create LVM logical volume?

Java Administration

  • What is the JVM?
  • Describe garbage collection.
  • What are the types of garbage collectors?
  • Walk me through a garbage collection, what happens?
  • What are the heap generations?
  • Describe the young heap spaces.
  • What is stored in the To space of a young generation
  • How do you set the heap size?

Apache

  • What is the basic directory structure?
  • What files are contained in /etc/httpd/conf.d?
  • What is virtual hosting?
  • What are the types of virtual hosts?
  • What is meaning of "Listen" in httpd.conf file?
  • What is DocumentRoot?
  • Can I serve content out of a directory other than the DocumentRoot directory?
  • Which tool you have used for Apache benchmarking?
  • You are getting following codes (2xx, 3xx, 4xx, 5xx) in Apache, at some point of time. What does this means?
  • Can we have two Apache Web servers on a single machine?
  • Which of the following best explains why Apache Web servers are able to handles multiple requests? A. Apache is able to spawn child processes that handle requests before they die.
  • What does DSO stands for?

Redhat

  • What is RPM?
  • What is YUM?
  • Explain the differences.
  • What does /boot directory contains?
  • What does /dev directory contain?
  • If you are getting error "package is already installed" but you have to install package any how. what option you will use?
  • How to install Linux software’s by RPM?
  • How Many Run Levels present in Linux?
    • 0: Halt the system
    • 1: Single-user mode
    • 2: Not used
    • 3: Multi-user mode with text login
    • 4: Not used
    • 5: Multi-user mode with graphical login
    • 6: Reboot
  • What is the default runlevel for a server?
  • Explain /proc filesystem?

Puppet

  • What is Puppet?
  • What is Manifests?
  • What is Module and How it is different from Manifest?
  • What is Facter?

Shell

  • What does . mean in regular expressions?
  • What is difference between ” and ‘?
  • What does $? give you?
  • You might have heard about inodes. can you describe inode briefly?
    • A ‘inode’ is a ‘data-structure’, which is used for file identification on Linux. Each file on an Unix System has a separate ‘inode’ and an ‘Unique’ inode Number.
  • What is the difference between $$ and $!?

DNS

  • which are the important configuration files for DNS server ?
  • On which port DNS server works ?

Other Great References:

Some questions are 'borrowed' from other great references like: