Tuesday, 10 July 2012

Unix/Linux System Admin Interview Questions And Answers 9

Q: - What is the difference between LILO and GRUB ?
 1) LILO has no interactive command interface, whereas GRUB does.
2) LILO does not support booting from a network, whereas GRUB does.
3) LILO stores information regarding the location of the operating systems it can to load physically on the MBR.
If you change your LILO config file, you have to rewrite the LILO stage one boot loader to the MBR. Compared with GRUB, this is a much more risky option since a misconfigured MBR could leave the system unbootable. With GRUB, if the configuration file is configured incorrectly, it will simply default to the GRUB command-line interface.
Q: - What is LVM Snapshot ?
 An LVM snapshot is an exact copy of an LVM partition that has all the data from the LVM volume from the time the snapshot was created. The big advantage of LVM snapshots is that they can be used to greatly reduce the amount of time that your services/databases are down during backups because a snapshot is usually created in fractions of a second. After the snapshot has been created, you can back up the snapshot while your services and databases are in normal operation.
Q: - How to verify the signature of an rpm ?
rpm -K test-1.0-1.i386.rpm
Q: - What is the meaning of  Hard & soft mount option in NFS server ?
Hard mount
- If the NFS file system is hard mounted, the NFS daemons will try repeatedly to contact the server. The NFS daemon retries will not time out, will affect system performance, and you cannot interrupt them
Soft mount 
- If the NFS file system is soft mounted, NFS will try repeatedly to contact the server until either:
  • A connection is established
  • The NFS retry threshold is met
  • The nfstimeout value is reached

Q: - What is an inode ?
 An inode is a data structure on a traditional Unix-style file system such as UFS. An inode stores basic information about a regular file, directory, or other file system object.
When a file system is created, data structures that contain information about files are created. Each file has an inode and is identified by an inode number (often "i-number" or even shorter, "ino") in the file system where it resides. Inodes store information on files such as user and group ownership, access mode (read, write, execute permissions)
and type of file. There is a fixed number of inodes, which indicates the maximum number of files each filesystem can hold.
Q: - What is the role of udev daemon in Unix ?
 udev is the device manager for the Linux 2.6 kernel series. Primarily, it manages device nodes in /dev. It is the successor of devfs and hotplug, which means that it handles the /dev directory and all user space actions when adding/removing devices, including firmware load.
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: - 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 is Super Block in Linux/Unix ?
Each file system is different and they have type like ext2, ext3 etc.Further eachfile system has size like 5 GB, 10 GB and status  such as mount status. In short each file system has a superblock, which contains informationabout file system such as:
  File system type
  • Size
  • Status
  • Information about other metadata structures
            If this information lost, you are in trouble (data loss) so Linux             maintains multiple redundant copies of thesuperblock in every file             system. This is very important in many emergency situation, for             example you can usebackup copies to restore damaged primary             super block.

Following command displays primary and backup superblock location on/dev/sda3:

# dumpe2fs /dev/hda3 | grep -i superblock

Q: - What is the load average of the server and What is an acceptable Server Load Average ?
The load average is the sum of the run queue length and the number of jobs currently running on the CPUs. The three load-average values in the first line of top output are the 1-minute, 5-minute and 15-minute average. (These values also are displayed by other commands, such as uptime, not only top.)
There are a few factors involved to determine the server average load. If your server (s) use dual processors, the acceptable Server Load Average is 2.00. This load is considered "optimal".

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