Category Archives: linux

Update NTP server in Linux Application

We use the NTP protocol to sync the time of servers,network devices, client PC’s with our local time zone to keep the correct time over the network. This can be accomplished through a NTP server configured locally in our network which will have the capability to receive and update the local time from the satellites in space.

The time which they get updated will be set as a bench mark over the entire machines over its network if this machine is configured as NTP server for them. This article focusses on updating the local NTP server on linux application.

To See Current Date –

Putty ssh to the server and run –    date

To check the ntp service status run –   service ntpd status

NTP1

To set your as NTP server  to get up to date time from them  run below  –

ntpdate ntpserverfqdn

Example – ntpdate ntp.exchangequery.local

Once after we updated we will get the below message

ntpdate Step time server offset sec
ntpdate adjust time server offset sec

To sync hardware clock –

hwclock –systohc

Reason to run above command: There are 2 types of clocks in Linux Operating systems.

1) Hardware clock – is the battery powered “Real Time Clock” (also known as the “RTC”, “CMOS clock”) which keeps track of time when the system is turned off but is not used when the system is running.

2) System clock-  (sometimes called the “kernel clock” or “software clock”) which is a software counter based on the timer interrupt.

This  above command will Set the Hardware Clock to the current System Time which will update from the local ntp server in our environment.

Note: We have an option to set the Hardware Clock from the System Time, or set the System Time from the hardware Clock.

Finally we need to Add the NTP server in the ini.config

Navigate via VI to ntp.conf location –  vi /etc/ntp.conf

vi /etc/sysconfig/ntpdate

NTP

Finally restart the ntp service –

service ntpd  restart

There is another option to update the servers from the website ntp.pool.org

We can go to this official ntp pool site and choose our continent area servers.

In order to update them VI to the ntp location :

vi /etc/ntp.conf

We can see the default ntp servers like below. We can comment them and need to update with the correct servers for the respective country where the server is hosted.

NTP2

In my example updating with my local time zone as below and commenting the default ones.

NTP3

After the above is completed the servers will be updated.

We can check the ntp peers synchronization with the below command

ntpq -p

Based on our requirement we can set the ntp server to be our local ntp server or one from the local time zone and after this the linux server will be updated with the latest current local time zone.

Thanks & Regards
Sathish Veerapandian

Extending the existing storage on Linux applications

It can happen that we arrive at a point where the storage is not sufficient or reached the maximum level on the Linux Servers.
In this case we need to add a new  physical disk ,create a physical volume and extend the existing  logical volumes assigned on the Linux based application.

There are many ways of doing this job.
In this article we will have a look at one step to accomplish this activity.
Before assigning the new physical disk  to the application  we need to check the below values.

Open Putty session ssh to the Linux server and run the below commands in order.
a. fdisk –l

This Fdisk command line utility is very useful in terms of creating space for new partitions, organising space for new drives, re-organizing an old drives and copying or moving data to new disks. It allows us to create a maximum of four new primary partition and number of logical (extended) partitions, based on size of the hard disk we have in our system.

In our case we use the above command to View all Disk Partitions their size and their name  in Linux system

Linux

b. pvs

This reports information about physical volumes.
pvs produces formatted output about physical volumes.
In our case we use this to check the current physical volume size.

Linux1

c. vgs
vgs command provides volume group information in a configurable form, displaying one line per volume group. The vgs command provides a great deal of format control, and is useful for scripting.
We are using this to display properties of LVM volume groups

Linux1

d. df 

To get the VG name and LVNAME

df displays the amount of disk space available on the file system containing each file name argument. If no file name is given, the space available on all currently mounted file systems is shown.
In our case why we are using this is to check the current free space on the disks currently assigned.

Linux2
Also we get the current disk VG and LV names ,so that we run the LV extend on them after assigning the new disk in the next steps.

Now we need to follow the below steps after assigning the new disk

a. fdisk –l
Now after assigning the new disk we need to Compare the output from previous step fdisk output to find out the new disk name.

After identifying the new disk name we need to create the Physical Volume.

b. pvcreate /dev/sd<New Disk>

After we get the new disk name from the previous output we should run the above command with the new disk name.
Here we are actually choosing the newly assigned physical volumes that will be used to create the LVM.
We can create the physical volumes on the linux system using pvcreate command.

c. lvextend –lvresize +200GB /dev/VGNAME/LVNAME

lvresize can be used for both operations (shrinking and/or extending) The lvresize will resize only the virtual volumes.
In our case we are using this command utility to the newly added space to resize the existing LVs.

There are few other options to extend the logical volume. By using the above command syntax we are reserving additional 200 GB space on this physical disk.
This 200 GB free space can be extended any time online to any LV’s without need for a reboot or bringing down the application if we run out of space for the file system  in future.

So It is always important to include the plus (+) signs while resizing a logical volume.
If we don’t do this then we are setting a fixed size for the LV instead of resizing it.

d. Finally after all the above steps are done we can run pvs
After running PV’s we can Compare the output from previous step output of PVS;
After the comparison the we need to extend new  volume group by the below command.

resize2fs /dev/sd<newdisk>

Note:
Its very important to note that you need to understand how the LV’s , PV’s & VG’s are created and assigned on the Linux application.
Also do this only if you have worked and having knowledge on the Linux systems.
If you are not sure on this its always better to perform this action with Linux Admin.

Thanks & Regards
Sathish Veerapandian
MVP – Office Services & Servers

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