Saturday, July 11, 2015

linux interview questions and answers on file system

1.         Name the Linux specific partition types?
Ans.    0x82                     >          Linux swap
            0x83                     >          Linux
            0x8e                      >          Linux LVM
            0xfd                      >          Linux RAID auto
            0x5                        >          Extended
            0xf                         >          Windows partition
2.         How many partitions are supported by Linux?
Ans.       The maximum number of partitions supported by Linux kernel is:
            63 for IDE drives , 15 for SCSI drives
3.         Why partitions required?
Ans. Separate partitions improve performance by keeping data together which reduces the disk head seek.
4.         What are the tools used to create or manage partitions?
Ans.      Fdisk,  sfdisk             parted (GNU) - An advanced partition manipulation tool (create, copy,    resize etc.)
5.         What is the function of partprobe?
Ans.              Reinitializes the kernel's in memory copy of the partition table.
6.         How to create a filesystem?
Ans.      The mkfs command is used to create the filesystem.
            mkfs.ext2 / mkfs.ext3     >          To create ext2/ext3 filesystem
            mkfs.minix                       >          minix filesystem
            mkfs.msdos                      >          MS-DOS filesystem

7.         What is the difference between ext2 and ext3 filesystem?
Ans.        ext3 filesystem supports journaling, where as ext2 does not.
9.         What are the journaling modes supported by ext3 filesystem?
Ans.      Ordered                >          Journals only metadata (This is the default)
            Journaled              >          Journals data as well as metadata
            Writeback            >          Journal updates are not atomic, but this gives
                                                      better performance.
10.       How to convert an ext2 filesystem to ext3?
Ans       Change the /etc/fstab to specify ext3 for desired filesystem(s)
            Create the ext3 journal on the ext2 filesystem(s) as:
            # tune2fs  -j 
            If the kernel needs to have access to the ext3 module at boot time, create  a new initial ramdisk as:
            # mkinitrd  /boot/initrd-.img
11.       How to connect a file system to a Linux box?
Ans.           Mount command is used.
12.      How to find currently mounted and available filesystems?
Ans.  Use mount command without arguments.
13.      Which filesystem is referred by mount when displaying mounted & available filesystems?
Ans.   When mount command is invoked without any arguments it referes to the /etc/mtab filesystem.
14.      How to disconnect a filesystem from a Linux box?
Ans.             The umount command is used.
15.      Which command is used to display information about the processes using a filesystem?
Ans.            The fuser command is used.

16.      How to display who/what is acting on a filesystem?
Ans.            # fuser  -v  mnt_point
17.      How to kill all actions on a filesystem?
Ans.                  # fuser  -km  mnt_point
18.      How to view all the mounted and unmounted partitions?
Ans.     Use the fdisk -l command to view all the mounted and unmounted
             filesystems available on your system.   
19.      How to view only the mounted filesystems?
Ans. Use the df -k command, which shows only mounted filesystems but has the big advantage of giving you the mount points too.
20.      What is the function of e2label command?
Ans. With the help of e2label command a filesystem label can be written into the superblock of ext2/ext3 filesystem.
Eg:-           #e2label  /dev/hda3  datadisk3
 Will create a label of datadisk3 on the filesystem on partition /dev/hda3.
21.      How to display the label for a device (/dev/hdb2)?
Ans.             # e2lable  /dev/hdb2
 22.      What is the function of /etc/fstab?
Ans.  This file is referenced each time the system boots to create the desired filesystem hierarchy.
23.      What are the fields /etc/fstab containd?
Ans.            The /etc/fstab fields are:
                  Device                        >          Special device/filesystem
                                                                   label dev to mount
                  Mount_Point             >          The path used to access the
                  fs_type                       >          The filesystem type
                  Options                       >          List of Options (each is
                                                                   separated by a comma)
                  Dump frequency        >          Level 0 dump freq (0 = never
                                                                  dump, 1 = daily &
                                                                  2 = every other day)
                  fsck Order                  >         0 = ignore, 1 = first (root
                                                                  should have this value),
                                                                  2 to 9 = 2nd, 3rd and so on.
                                                                  NFS & CD-ROM s should                                                                    be ignored (i.e., value 0).

24.      How to list the ext2/ext3 filesystem attributes?
Ans.    lsattr  command displays file attributes

25.      How to change the ext2/ext3 filesystem attributes?
      Ans.   chattr command changes the file attributes.

26.    What is swap space?
Ans.  Swap space is supplement to system RAM.

27.    How to set up swap partition?
Ans.  Steps involved in setting up swap partition.
         Create a partition using a partitioning program (fdisk/sfdisk/parted)
         Set partition id type to 0x82.
         Create the signature on the partition using the mkswap command
         # mkswap  -v1  /dev/hdb3
        Add an entry for the swap in /etc/fstab file as:
        /dev/hdb3   swap   swap   defaults    0   0
        Activate the swap partition using
        # swapon -a
        Check the swap partition status using
        # swapon  -s

28.    How to create a swap file?
Ans.  Create a file as
         # dd  if=/dev/zero  of=swapfile   bs=512  count=N
         (Where N is the file size in KB)
         Run the mkswap to create signature
         Activate the swap file with swapon command (OR) initialize it in the startup
         script /etc/rc.d/rc.local

29.    Why fsck used?
Ans.  fsck (filesystem check) is used to maintain filesystem consistency.

30.    When the system runs the fsck and which script invokes it?
Ans.  When the system boots,  the rc.sysinit script runs the fsck on any filesystems
         marked for checking in /etc/fstab file. If any of these filesystems are markes as 
         dirty or have data in the journal, fsck will attempt to repair them. If it succeeds,
         the filesystems will be mounted and boot process continues, else rc.sysinit will
         run sulogin and will report that fsck needs to be run manually.

31.    What is e2fsck command?
Ans.  fsck is a front end tool for e2fsck.

32.    What is journaling?
33.    Types of journals and their function?
Ans.  Ordered          :    This is the default and journal only meta-data
         Journaled        :    Journals data and meta-data
         Writeback       :    Journal updates are not atomic.

34.    Differentiate ext2 and ext3 file systems?
Ans.  ext3 filesystem supports journaling concept where ext2 does not.

35.    What is the function of tune2fs command?
Ans.  This is used to modify the filesystem attributes (Like converting ext2 to ext3).

36.    What is the function of dump2fs command?
Ans.  Provides a dump of file system information to standard out (Console). Can be
         redirected to a file.

37.    What is the function of debugfs command?
Ans.  This utility is used to to examine and debug an ext2 filesystem. This can also be
         used to manually verify the inode integrity and an aid to recover data.

38.    What is the function of resize2fs command?
Ans.  This can be used to change the size of an ext2 or ext3 filesystem.

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