Interview Questions and Answers - Linux Administrator - 3

What is the major difference between ext2 and ext3 file systems?

The main difference between ext2 and ext3 is, ext3 allows journaling. (Journaling is a type of log file, which tracks all the file system changes. so that you can recover in case of filesystem crash)

Explain Linux Booting Process?

• When the computer is switched on, it automatically invokes BIOS [a ROM chip embedded in the motherboard].

• The BIOS will start the processor and perform a POST [power on self test] to check whether the connected device are ready to use and are working properly.

• Once the POST is completes BIOS will check for the booting device. The boot sector is always the first sector of the hard disk and BIOS will load the MBR into the memory. MBR holds the boot loader of the OS.

• From here the boot loader takes the control of the booting process.

• GRUB is the boot loader for Linux. 

• Depending on the boot option selected the kernel is loaded first.

• After kernel is loaded the kernel will take the control of the booting process

• Initrd will be loaded which contains drivers to detect hardware (Initialization of RAM Disk)

• Then it will initialize all the hardware including I/O processors etc.

• Kernel then mounts the root partition as read-only

• INIT is loaded as the first process.

• INIT will mount the root partition and other partitions as read/write and checks for file system errors.

• Sets the System Clock, hostname etc..

• Based on the Runlevel, it will load the services and runs the startup scripts which are located in /etc/rcX.d/ (Network, cups, nfs, SSH etc.)

• Finally it runs the rc.local script.

• Now the login prompt will appear.

How do you extend a LV? For example, How do you expand /var file system with additional 2GB space?

• Check which logical volume (LV) holds the  /var file system using df –h
• Now, find out this particular LV belongs to which VG using lvdisplay <lv_name>
• Check the free space available in that Volume Group (VG) using vgdisplay <vgname>. Look for "Free PE / Space" line in the ouput.
• If the free space available in VG, now you can expand the LV using lvextend –L +2G <lv_name>. Now, Logical Volume has been expanded. Now we have to expand the file system using resize2fs /var. All these can be done in online without unmounting the filesystems.

How do you find out hardware errors inside Linux?

• dmesg
• /var/log/messages
• dmidecode –t system 
• IML (Integrated Management Logs) - An iLO console feature
• hpacucli - To check RAID array status
• use grep or less commands on

• /var/log/messages and /var/log/warn
• /var/log/debug
• /var/log/kern.log
• /var/log/mcelog

How do find out what are the files inside an RPM before installing it?

rpm -qlp package.rpm  (Example : $ rpm -qlp rpm -qlp gnupg-1.4.5-1.i386.rpm)

Interview Questions and Answers - Linux Administrator - 2

What command can you use to review boot messages?

The dmesg command can be used to display the system messages during boot time.

What are the fields in the /etc/passwd file. Explain them?

There are 7 fields in /etc/passwd:

username:x:UID:GID:comment:home directory:shell

1)Username.
2)Password. Dummy value x denotes that its using shadow passwords

3)UID.

4)Primary group ID.
5)Comment /description.
6)Home directory path.
7)Shell assigned to the user.

Whats the journaling data contains in ext3? 

A journaled file system records information in a log area on a disk.   It logs the "metadata" i.e ownership, date stamp information etc..Once the log is updated the system then writes the actual data to the appropriate areas of the filesystem and marks an entry in the log to say the data is committed.

After a crash the filesystem can very quickly be brought back on-line using the journal logs 

using fsck there is considerably less chance of data loss or corruption.

How do u extend the LV in Linux?

First check whether is there free space available in the VG where the LV resides.

# vgdisplay or 

# vgs

Now, extend the LV using below command: "L" option to specify the size to be increased.

# lvextend -L +5G /dev/vg00/lv01

Finally, extend the File system space:

# resize2fs /dev/vg00/lv01

That's all..!  Look at the other posts as well for interview questions. I am posting 4-5 questions in every post whenever i get time.

Interview Questions and Answers - Linux Administrator

1.  How do u force a user to change password on next login in linux?

A.  chage -d 0 "User"

2.What command can be used to findout server architechure (x86 or x64) apart from 

    uname?

A. arch

3. How do u findout the users who are NOT logged in for more than 30 days? which file u 

    will check?

A. last , lastlog,   /var/log/wtmp

4. whats is called 1.5 stage in boot process of linux?

A. Which contains extra code to allow cylinders above 1024, or LBA type drives, to be read. The  

    1.5 boot loader is stored (if needed) in the MBR or the boot partition.The great thing about  

    GRUB is that it includes knowledge of Linux file systems. Instead of using raw sectors on the 

    disk, as LILO does, GRUB can load a Linux kernel from an ext2 or ext3 file system. It does this 

    by making the two-stage boot loader into a three-stage boot loader. Stage 1 (MBR) boots a 

    stage 1.5 boot loader that understands the particular file system containing the Linux kernel 

    image. Examples include reiserfs_stage1_5 (to load from a Reiser journaling file system) or  

   e2fs_stage1_5 (to load from an ext2 or ext3 file system). When the stage 1.5 boot loader is   

    loaded and running, the stage 2 boot loader can be loaded."

    So Basically,

    Stage 1 Boot loader is MBR

    Stage 2 Boot loader is GRUB

    Stage 1.5 Boot loader is e2fs_stage1_5 

    (Basically this module will load the knowledge of Filesystem to Grub to read the kernel)

5. When u try to create a file, u got a error that "No space available". But actually space  

     available on volume? How do u resolve this issue?

A. Try this df -i   list inode information instead of block usage [Perhaps are you out of inodes on 

    this file system.], To "rectify it", remove unwanted files or move them somewhere else.]