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Thursday, March 24, 2016

How to Reduce File System Size on Linux

How to Reduce File System Size on Linux


Before starting, it is always good to backup the data, if something goes wrong. Easily restore from backup.

To Reduce a logical volume / file system there are 5 steps needed to be done very carefully.
While extending a volume we can extend it while the volume under mount status (online) but for reduce we must need to unmount the file system before reducing.

Fallow the below 5 steps


  • unmount the file system for reducing.
  • Check the file system after unmount.
  • Reduce the file system.
  • Reduce the Logical Volume size than Current size.
  • Recheck the file system for error.
  • Remount the file-system back to stage.


Step 1:

mohan@root# lvs

  LV      VG           Attr   LSize   Origin Snap%  Move Log Copy%  Convert
  lv_home vg_test01 -wi-ao 431.79g
  lv_root vg_test01 -wi-ao  50.00g
  lv_swap vg_test01 -wi-ao  17.72g

mohan@root# df -h

Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_test01-lv_root
                       50G  4.9G   42G  11% /
tmpfs                 7.8G   88K  7.8G   1% /dev/shm
/dev/sda1             485M   35M  425M   8% /boot
/dev/mapper/vg_test01-lv_home
                      426G  199M  404G   1% /home

mohan@root# umount -v /home
/dev/mapper/vg_test01-lv_home umounted

Step 2:

mohan@root# e2fsck -ff /dev/mapper/vg_test01-lv_home
e2fsck 1.41.12 (17-May-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/mapper/vg_test01-lv_home: 11/28303360 files (0.0% non-contiguous), 1827094/113190912 blocks

Step 3:

mohan@root# resize2fs /dev/mapper/vg_test01-lv_home 250G
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/mapper/vg_test01-lv_home to 65536000 (4k) blocks.
The filesystem on /dev/mapper/vg_test01-lv_home is now 65536000 blocks long.


Step 4:

mohan@root# lvreduce -L -250G /dev/mapper/vg_test01-lv_home
  WARNING: Reducing active logical volume to 181.79 GiB
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce lv_home? [y/n]: y
  Reducing logical volume lv_home to 181.79 GiB
  Logical volume lv_home successfully resized

Step 5


mohan@root# mount /home (or) mount -f /home
mohan@root# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_test01-lv_root
                       50G  4.9G   42G  11% /
tmpfs                 7.8G   88K  7.8G   1% /dev/shm
/dev/sda1             485M   35M  425M   8% /boot
/dev/mapper/vg_test01-lv_home
                       50G  4.9G   42G  11% /home


Successfully reduced /home file system size.



Sunday, March 20, 2016

Cisco Network Time Protocol (NTP) and Change Time format to Indian Standard (IST)


Cisco Network Time Protocol (NTP) and Change Time format to IST Indian Standard

NTP (Network Time Protocol) is used to allow network devices to synchronize their clocks with a central source clock. For network devices like routers, switches or firewalls this is very important because we want to make sure that logging information and time stamps have the accurate time and date.

MOHAN-SUNDARAM#show clock
*14:09:12.784 UTC Sun Mar 18 2016 --> Incorrect timezone.

How to Change Time / Date format to IST Indian Standard, Try below commands

MECT-D-Block-SW#conf t
Enter configuration commands, one per line.  End with CNTL/Z.

MECT-D-Block-SW(config)#clock timezone UTC +5 30

MOHAN-SUNDARAM(config)#do show clock
*15:12:59.784 UTC Sun Mar 20 2016

How to Configure Cisco Switch / Firewall  NTP Server:-

MOHAN-SUNDARAM(config)#do show clock
*15:12:59.784 UTC Sun Mar 20 2016  -->  Still showing incorrect time and Clock unsynchronized.

MOHAN-SUNDARAM#show ntp status
Clock is unsynchronized, stratum 16, no reference clock
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**10
reference time is 00000000.00000000 (05:30:00.000 UTC Mon Jan 1 1900)
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 50.12 msec, peer dispersion is 0.00 msec
loopfilter state is 'FSET' (Drift set from file), drift is 0.000000000 s/s
system poll interval is 8, never updated.

Try below step by step commands.

Step 1:

Use Google DNS Server.

MOHAN-SUNDARAM(config)#ip name-server 8.8.8.8

Step 2:

Synchronize using clock with the public NTP server.

MOHAN-SUNDARAM(config)#ntp server pool.ntp.org
Translating "pool.ntp.org"...domain server (8.8.8.8) [OK]


Above we see the show ntp associations command that tells us if our clock is synchronized or not. The ~ in front of the IP address tells us that we configured this server but we are not synchronized yet. You can see this because there is no * in front of the IP address and the “st” field (stratum) is currently 3.


Step 3:

MOHAN-SUNDARAM(config)#do show ntp associations

  address         ref clock       st   when   poll reach  delay  offset   disp
*~123.108.200.124 125.62.193.121   3      4     64     1 46.982   1.985 188.53
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~ configured


Step 4:

MOHAN-SUNDARAM(config)#do show ntp status
Clock is unsynchronized, stratum 16, no reference clock
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**10
reference time is 00000000.00000000 (05:30:00.000 UTC Mon Jan 1 1900)
clock offset is 0.0000 msec, root delay is 0.00 msec
root dispersion is 50.12 msec, peer dispersion is 0.00 msec
loopfilter state is 'FSET' (Drift set from file), drift is 0.000000000 s/s
system poll interval is 8, never updated.


The router tells us that we are unsynchronized and that there is no reference clock.
we will just wait a couple of minutes and take a look at these commands again.


MOHAN-SUNDARAM(config)#do show ntp status

Clock is synchronized, stratum 4, reference is 123.108.200.124
nominal freq is 250.0000 Hz, actual freq is 250.0000 Hz, precision is 2**10
reference time is DA994010.8C49BBE0 (20:58:16.548 UTC Sun Mar 20 2016)
clock offset is 1.9850 msec, root delay is 356.06 msec
root dispersion is 4047.21 msec, peer dispersion is 188.53 msec
loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000000000 s/s
system poll interval is 64, last update was 28 sec ago.

Step 5:

NTP Server time updated successfully.

MOHAN-SUNDARAM#show clock detail
*14:39:41.930 UTC Sun Mar 20 2016
Time source is NTP