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Monday, April 18, 2011

Linux Admin Q&A

Interview Questions And Answers

Q: - How are devices represented in UNIX?

All devices are represented by files called special files that are located in /dev directory.

Q: - What is 'inode'?

All UNIX files have its description stored in a structure called 'inode'. The inode contains info about the file-size, its location, time of last access, time of last modification, permission and so on. Directories are also represented as files and have an associated inode.

Q: - What are the process states in Unix?

As a process executes it changes state according to its circumstances. Unix processes have the following states:

Running : The process is either running or it is ready to run .
Waiting : The process is waiting for an event or for a resource.
Stopped : The process has been stopped, usually by receiving a signal.
Zombie : The process is dead but have not been removed from the process table.

Q: - What command should you use to check the number of files and disk space used and each user's defined quotas?

repquota

Q: - What command is used to remove the password assigned to a group?

gpasswd -r

Q: - What can you type at a command line to determine which shell you are using?

echo $SHELL

Q: - Write a command to find all of the files which have been accessed within the last 30 days.

find / -type f -atime -30 > filename.txt

Q: - What is a zombie?

Zombie is a process state when the child dies before the parent process. In this case the structural information of the process is still in the process table.

Q: - What daemon is responsible for tracking events on your system?

syslogd

Q: - What do you mean a File System?

File System is a method to store and organize files and directories on disk. A file system can have different formats called file system types. These formats determine how the information is stored as files and directories.

Q: - Tell me the name of directory structure hierarchy for Linux

/root
/boot
/bin
/sbin
/proc
/mnt
/usr
/var
/lib
/etc
/dev
/opt
/srv
/tmp
/media  

Q: - What does /boot directory contains?

The /boot/ directory contains static files required to boot the system, such as the Linux kernel, boot loader configuration files. These files are essential for the system to boot properly.

Q: - If some one deletes /boot directory from your server, than what will happen?

In that case your server will be in unbootable state. Your Server can’t boot without /boot directory because this directory contains all bootable files

Q: - What does /dev directory contain?

The /dev directory contains all device files that are attached to system or virtual device files that are provided by the kernel.

Q: - What is the role of udev daemon?

The udev demon used to create and remove all these device nodes or files in /dev/ directory.

Q: - What kind of files or nodes /dev/ directory contains and how do I access or see device files?

Block Device Files:-

Block device files talks to devices block by block [1 block at a time (1 block = 512 bytes to 32KB)].
Examples: - USB disk, CDROM, Hard Disk

# ls /dev/sd*brw-rw----         1 root          root            8,      0 Mar 15  2009 sda
brw-rw----      1 root          root            8,      1 Mar 15  2009 sda1
brw-rw----      1 root          root            8,      2 Mar 15  2009 sda2
brw-rw----      1 root          root            8,      3 Mar 15  2009 sda3
brw-rw----      1 root          root            8,      4 Mar 15  2009 sda4
brw-rw----      1 root          root            8,      16 Mar 15  2009 sdb

Character Device Files:-

Character device files talk to devices character by character.
Examples: - Virtual terminals, terminals, serial modems, random numbers

#ls /dev/tty*crw-rw----         1 root          root            4,      64 Mar 15  2009 ttyS0
crw-rw----      1 root          root            4,      65 Mar 15  2009 ttyS1
crw-rw----      1 root          root            4,      66 Mar 15  2009 ttyS2
crw-rw----      1 root          root            4,      67 Mar 15  2009 ttyS3

Q: - Tell me the name of device file for PS/2 mouse connection.

/dev/psaux

Q: - Tell me the name of device file for parallel port (Printers).

/dev/lp0

Q: - What does /etc/X11/ directory contains?

The /etc/X11/ directory is for X Window System configuration files, such as xorg.conf.

Q: - What does /etc/skell directory contains?

The /etc/skel directory contains files and directories that are automatically copied over to a new user's home directory when such user is created by the useradd or adduser command.

Q: - Tell me name of Linux File systems?

Ext2
Ext3

Q: - What is the difference between ext2 and ext3 file systems?

The ext3 file system is an enhanced version of the ext2 file system.

The most important difference between Ext2 and Ext3 is that Ext3 supports journaling.
After an unexpected power failure or system crash (also called an unclean system shutdown), each mounted ext2 file system on the machine must be checked for consistency by the e2fsck program. This is a time-consuming process and during this time, any data on the volumes is unreachable.
The journaling provided by the ext3 file system means that this sort of file system check is no longer necessary after an unclean system shutdown. The only time a consistency check occurs using ext3 is in certain rare hardware failure cases, such as hard drive failures. The time to recover an ext3 file system after an unclean system shutdown does not depend on the size of the file system or the number of files; rather, it depends on the size of the journal used to maintain consistency. The default journal size takes about a second to recover, depending on the speed of the hardware.

Q: - Any idea about ext4 file system?

The ext4 or fourth extended filesystem is a journaling file system developed as the successor to ext3. Ext4 filesystem released as a functionally complete and stable filesystem in Linux with kernel version 2.6.28.

Features of ext4 file system:-

1. Currently, Ext3 supports 16 TB of maximum file system size and 2 TB of maximum file size. Ext4 have 1 EB of maximum file system size and 16 TB of maximum file size.

[An EB or exabyte is 1018 bytes or 1,048,576 TB]
2. Fast fsck check than ext3
3 In Ext4 the journaling feature can be disabled, which provides a small performance improvement.
4. Online defragmentation.
5. Delayed allocation
Ext4 uses a filesystem performance technique called allocate-on-flush, also known as delayed allocation. It consists of delaying block allocation until the data is going to be written to the disk, unlike some other file systems, which may allocate the necessary blocks before that step.

Q: - How we create ext3 file system on /dev/sda7 disk?

# mkfs –j /dev/sda7

Q: - Can we convert ext2 filesystem to ext3 file system?

Yes, we can convert ext2 to ext3 file system by tune2fs command.

                tune2fs –j   /dev/

Q: - Is there any data lose during conversion of ext2 filesystem to ext3 filesystem?

No

Q: - How we will create ext4 file system?

# mke2fs -t ext4 /dev/DEV

Q: - Explain /proc filesystem?

/proc is a virtual filesystem that provides detailed information about Linux kernel, hardware’s and running processes. Files under /proc directory named as Virtual files. Because /proc contains virtual files that’s why 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, like the /proc/filesystems file and the /proc/sys/ directory provide system configuration information and interfaces.

Q: - Can we change files parameters placed under /proc directory?

Yes
To change the value of a virtual file, use the echo command and a greater than symbol (>) to redirect the new value to the file. For example, to change the hostname on the fly, type:

echo www.nextstep4it.com > /proc/sys/kernel/hostname

Q: - What is the use of sysctl command?

The /sbin/sysctl command is used to view, set, and automate kernel settings in the /proc/sys/ directory.

Q: - Explain /proc filesystem?

/proc is a virtual filesystem that provides detailed information about Linux kernel, hardware’s and running processes. Files under /proc directory named as Virtual files. Because /proc contains virtual files that’s why 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, like the /proc/filesystems file and the /proc/sys/ directory provide system configuration information and interfaces.

Q: - Can we change files parameters placed under /proc directory?

Yes
To change the value of a virtual file, use the echo command and a greater than symbol (>) to redirect the new value to the file. For example, to change the hostname on the fly, type:

echo www.nextstep4it.com > /proc/sys/kernel/hostname

Q: - What is the use of sysctl command?

The /sbin/sysctl command is used to view, set, and automate kernel settings in the /proc/sys/ directory.



!Enjoy

Kuldeep Sharma