1. Name a service that you should disable (which acts both as Web and FTP Server) on a Linux Server.
The finger service should be disabled because a remote user can get important information about the system by using that command.

2. How shadow passwords are given by in Linux?
pwconv command is used for giving shadow passwords. Shadow passwords are given for better system security. The pwconv command creates the file /etc/shadow and changes all passwords to ‘x’ in the /etc/passwd file.

First, entries in the shadowed file which don’t exist in the main file are removed. Then, shadowed entries which don’t have `x’ as the password in the main file are updated. Any missing shadowed entries are added. Finally, passwords in the main file are replaced with `x’. These programs can be used for initial conversion as well to update the shadowed file if the main file is edited by hand.

3. What shell does a Linux Administrator assign to a POP3 mail-only account?
POP3 mail only account is assigned to the /bin/false shell. However, assigning bash shell to a POP3 mail only gives user login access, which is avoided. /bin/nologin can also be used. This shell is provided to the user when we don’t want to give shell access to the user. The user cannot access the shell and it rejects shell login on the server as in Telnet. It is mainly for the security of the shells.
POP3 is basically used for downloading mail to mail program. So for illegal downloading of emails on the shell, this account is assigned to the /bin/false shell or /bin/nologin. These both shells are same as they both do the same work of rejecting the user login to the shell.
The main difference between these two shells is that false shell shows the incorrect code and any unusual coding when user login to it. But the nologin shell simply tells that no such account is available. So nologin shell is used often in Linux.

4. What is YUM?
YUM stands for Yellow dog Updater, Modified because it is based on YUP, the Yellow dog Updater. Where does the name Yellow dog come from? Yellow Dog is a version of Linux for the Power Architecture hardware and is RPM-based, just like Red Hat Enterprise Linux and Fedora. YUP, and later YUM, were written by the Linux community as a way to maintain an RPM-based system

5. What is the role of Kudzu?
Kudzu is used to detect new Hardware. RedHat Linux runs a hardware discoverer, named kudzu. When attempting to identify a serial port Kudzu resets the serial port. This stops the serial console. Kudzu is configured from the file/etc/sysconfig/kudzu.
Kudzu can be prevented from resetting hardware, by setting the configuration parameter SAFE to yes.

6. Explain /proc filesystem?
/proc is a virtual file system that provides detailed information about Linux kernel, hardware and running processes. Files under /proc directory named as Virtual files.
Since /proc contains virtual files, it is called virtual file system. These virtual files have unique qualities. Most of them are listed as zero bytes in size.
Virtual files such as /proc/interrupts, /proc/meminfo, /proc/mounts, and /proc/partitions provide an up-to-the-moment glimpse of the system’s hardware. Others: /proc/filesystems file and the /proc/sys/ directory provide system configuration information and interfaces.

Also Read:- Top 10 Linux Interview Questions and Answers

7. How do you create ext4 file system?
# mke2fs -t ext4 /dev/DEV

8. How to Enable ACLs for /home partition?
Add following entry in /etc/fstab
LABEL=/home /home ext3 acl 1 2
Now remount /home partition with acl option.
mount -t ext3 -o acl /dev/sda3 /home

9. What is LILO?
LILO is Linux Loader is a boot loader for Linux. It is used to load Linux into the memory and start the Operating system. LILO can be configured to boot other operating systems as well. LILO is customizable, which means that if the default configuration is not correct, it can be changed. Config file for LILO is lilo.conf.
LILO is also a code snippet which loads PC BIOS into the main memory at the time of starting the computer system. It handles the following tasks :
1. Locating Linux kernel.
2. Identifying other supporting programs and loading them in the memory.
3. Starting Kernel.
The selection of various kernel images and boot routines is supported by LILO. For this reason, it is known as boot manager.

10. How to check Memory stats and CPU stats as a Linux admin?
Using ‘free’ & ‘vmstat’ command, we can display the physical and virtual memory statistics, respectively. With the help of ‘sar’ command, we can see the CPU utilization & other stats.

11. How to check and verify the status of the bond interface?
Using the command ‘cat /proc/net/bonding/bond0,’ we can check what mode is enabled and what LAN cards are used in this bond. In this example, we have one one bond interface. However, we can have multiple bond interfaces like bond1, bond2 and so on.

12. How can you enhance the security of password file?
Linux keep user account information in a text file called /etc/passwd. This file also stores one way encrypted password. It is accessed by several tools to get user information, which is a security risk, so file need to ‘Word Readable.’ To minimize the security risk, you can use shadow password format. This method saves account information in regular file /etc/passwd.

However, the password is stored as a single “x” character (not actually stored in this file). A second file, called “/etc/shadow” contains encrypted password as well as other information such as account or password expiration values, etc. The /etc/shadow file is readable only by the root account and is therefore less of a security risk.

13. What command can you use to make a tape archive file of a /home directory and send it to the /dev/tape device?
The correct command is tar -cvf /dev/tape /home.
The -xvf option is used to extract files from an archive.Expert Linux Professionals are in much demand.

14. Suppose your FTP Server is hacked and the entire server needs to be restored. How should you restore the original kernel system files?
You cannot restore the entire operating system from tape backup device. So you should reinstall the core operating system, and then restore system configuration files and user data from tape backup device.

15. Why should you avoid Telnet to administer a Linux system remotely?
Telnet uses most insecure method for communication. It sends data across the network in plain text format and anybody can easily find out the password using the network tool. In the case of Telnet, these include the passing of login credentials in plain text, which means anyone running a sniffer on your network can find the information he needs to take control of a device in a few seconds by eavesdropping on a Telnet login session.

16. What is Puppet Server?
Puppet is an open-source & enterprise software for configuration management toll in UNIX like operating system. Puppet is an IT automation software that is used to push configuration to its clients (puppet agents) using code. Puppet code can do multiple tasks from installing new software to checking file permissions to updating user accounts.

17. What command is used to check the number of files, disk space and each user’s defined quota?
repquota command is used to check the status of the user’s quota along with the disk space and number of files used.
This command gives a summary of the user’s quota that how much space and files are left for the user. Each user has a defined quota in Linux. This is done mainly for the security as some users have only limited access to files. This provides a security to the files from unwanted access. The quota can be given to a single user or to a group of users.

18. What is the name and path of the main system log?
By default, the main system log is ‘/var/log/messages’. This file contains all the messages and the script written by the user. By default, all scripts are saved in this file. This is the standard system log file, which contains messages from all system software, non-kernel boot issues, and messages that go to ‘dmesg’. dmesg is a system file that is written upon system boot.

19. You have lots of running jobs, how would you remove all the running processes, without restarting the machine?
The Linux command ‘disown -r’ will remove all the running Processes.

20. Who own the data dictionary?
The user ‘SYS’ owns the data dictionary. Users ‘SYS’ and ‘SYSEM are created by default, automatically.

Also Read:- Top 30 Linux Interview Questions and Answers

 


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