Sync Time using NTP

Most servers are probably automatically configured to network time, but if you want to set it up for yourself, or want to change the servers that you are syncing to, here’s the quick article that shows you how to do it.

Since I had to do this earlier today, I decided it would make a lot of sense to write it down for the next time that I need to do it. Yeah, this article is really just for me.

First, you’ll need to install NTP if it isn’t already installed. For Debian or Ubuntu, that would be this command:

sudo apt-get install ntp

For Redhat or CentOS, you’ll need to use this one:

yum install ntp

Then you’ll want to edit the /etc/ntp.conf file, which is quite possibly already filled out for you.

vi /etc/ntp.conf

You’ll find a lot of lines in there, but the important ones are the server lines. You can get a list of server addresses at www.pool.ntp.org, find the preferred ones for your area, and then add them to the file. For my purposes, that meant:

server 0.north-america.pool.ntp.org
server 1.north-america.pool.ntp.org
server 2.north-america.pool.ntp.org
server 3.north-america.pool.ntp.org

Then you’ll need to restart or start the NTPD service:

/etc/init.d/ntpd restart

If you want to update the time right now, you can stop the NTP service and then run the following command, swapping out your preferred server for pool.ntp.org.

/usr/sbin/ntpdate pool.ntp.org

Increase the size of /dev/shm

To increase the size of /dev/shm for oracle, please perform below steps

Add entry like below on /etc/fstab to make /dev/shm size 10GB

udev        /dev/shm   tmpfs          noauto,size=10g       0 0

Unmount and mount /dev/shm or reboot the server .

umount /dev/shm
mount /dev/shm

Check the size of /dev/shm

lnxsrv:~ # df -h /dev/shm
Filesystem      Size  Used Avail Use% Mounted on
udev             10G     0   10G   0% /dev/shm
lnxsrv:~ #

Extending Swap on an LVM2 Logical Volume

To extend an LVM2 swap logical volume (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend):


Disable swapping for the associated logical volume:
# swapoff -v /dev/VolGroup00/LogVol01
Resize the LVM2 logical volume by 256 MB:
# lvm lvresize /dev/VolGroup00/LogVol01 -L +256M
Format the new swap space:
# mkswap /dev/VolGroup00/LogVol01
Enable the extended logical volume:
# swapon -va
Test that the logical volume has been extended properly:
# cat /proc/swaps # free

HOW CAN I DISABLE THE FIREWALL ON SLES ?

HOW CAN I DISABLE THE FIREWALL ON SLES?

Believe it or not, there are valid reasons why you might want to disable the firewall service on a Suse Linux Enterprise Server (SLES).  For instance, avoiding NCP time-outs on client connections for an OES/SLES server.  If you just want to know how to disable the firewall in most modern incarnations of SLES, read on…

The examples given here are assuming you are remote to the server.  Of course, you could do all of this locally on the console, or adapt my instructions to the gui “Yast2″, but I’m going non-gui here for simplicity.

First, shell into the box, and su to root.

METHOD 1:

Launch the Yast non-gui firewall module:
yast firewall

To change to startup setting to “Manually”:
“Alt + m”

Optionally, to stop the service right now if running:
“Alt + t”

To complete the change:
“Alt + n”

To accept and finish:
“Alt + a”

METHOD 2:

To disable the service at next startup:
chkconfig SuSEfirewall2_setup off
chkconfig SuSEfirewall2_init off

Optionally, to stop the service right now if running:
rcSuSEfirewall2 stop

Rsync Remote Copy Example

Rsync is a utility available in linux which will help you to copy a file,folder (including sub folder) from a server to remote server . Rsync uses a quick and reliable algorithm to very quickly bring remote and host files into sync. Rsync is fast because it just sends the differences in the files over the network (instead of sending the complete files).

Below example  shows that to copy "app" folder from server1 to server2
--------------------------------------------------------------------------------------

[root@server1:/oracle]rsync -avz -e ssh app root@server2:/oracle/app

Crond & Anacron in Oracle Linux

In oracle Linux Anacron is using to schedule the cron job instead crond .
============================================================================

[root@serovm011~]# service anacron status
anacron is stopped
[root@serovm011~]# cat /etc/init.d/anacron


[root@serovm011~]# cat /etc/init.d/anacron
#!/bin/sh
# Startup script for anacron
#
# chkconfig: 2345 95 05
# description: Run cron jobs that were left out due to downtime
# pidfile: /var/run/anacron.pid
#

[root@serovm011 ~]# cat /etc/*release
Oracle VM server release 3.1.1

Virtual Machine(xen ) console access . Virsh command

Virtual Machine(xen ) console access .

Here is the example how to access a xen / virtual system console.

Eg : for accessing oracledbs

Login to Xen host  and sudo su to root

You can type “virsh” and you will be in virsh prompt.

Type help in “virsh#” it will list out all the commands

We can also execute virsh command directly from xen host machine

To start the virtual system

virsh start oracledbs –console

To connect the console

virsh console oracledbs

To list the virtual systems

Virsh list.

virsh # help

Commands:

    help            print help

    attach-device   attach device from an XML file

    attach-disk     attach disk device

    attach-interface attach network interface

    autostart       autostart a domain

    capabilities    capabilities

    cd              change the current directory

    connect         (re)connect to hypervisor

    console         connect to the guest console

    cpu-baseline    compute baseline CPU

    cpu-compare     compare host CPU with a CPU described by an XML file

    create          create a domain from an XML file

    start           start a (previously defined) inactive domain

    destroy         destroy a domain

    detach-device   detach device from an XML file

    detach-disk     detach disk device

    detach-interface detach network interface

    define          define (but don't start) a domain from an XML file

    domid           convert a domain name or UUID to domain id

    domuuid         convert a domain name or id to domain UUID

    dominfo         domain information

    domjobinfo      domain job information

    domjobabort     abort active domain job

    domname         convert a domain id or UUID to domain name

    domstate        domain state

    domblkstat      get device block stats for a domain

    domifstat       get network interface stats for a domain

    dommemstat      get memory statistics for a domain

    domblkinfo      domain block device size information

    domxml-from-native Convert native config to domain XML

    domxml-to-native Convert domain XML to native config

    dumpxml         domain information in XML

    edit            edit XML configuration for a domain

    find-storage-pool-sources discover potential storage pool sources

    find-storage-pool-sources-as find potential storage pool sources

    freecell        NUMA free memory

    hostname        print the hypervisor hostname

    list            list domains

    migrate         migrate domain to another host

    migrate-setmaxdowntime set maximum tolerable downtime

    net-autostart   autostart a network

    net-create      create a network from an XML file

    net-define      define (but don't start) a network from an XML file

    net-destroy     destroy a network

    net-dumpxml     network information in XML

    net-edit        edit XML configuration for a network

    net-list        list networks

    net-name        convert a network UUID to network name

    net-start       start a (previously defined) inactive network

    net-undefine    undefine an inactive network

    net-uuid        convert a network name to network UUID

    iface-list      list physical host interfaces

    iface-name      convert an interface MAC address to interface name

    iface-mac       convert an interface name to interface MAC address

    iface-dumpxml   interface information in XML

    iface-define    define (but don't start) a physical host interface from an XML file

    iface-undefine  undefine a physical host interface (remove it from configuration)

    iface-edit      edit XML configuration for a physical host interface

    iface-start     start a physical host interface (enable it / "if-up")

    iface-destroy   destroy a physical host interface (disable it / "if-down")

    managedsave     managed save of a domain state

    nodeinfo        node information

    nodedev-list    enumerate devices on this host

    nodedev-dumpxml node device details in XML

    nodedev-dettach dettach node device from its device driver

    nodedev-reattach reattach node device to its device driver

    nodedev-reset   reset node device

    nodedev-create  create a device defined by an XML file on the node

    nodedev-destroy destroy a device on the node

    nwfilter-define define or update a network filter from an XML file

    nwfilter-undefine undefine a network filter

    nwfilter-dumpxml network filter information in XML

    nwfilter-list   list network filters

    nwfilter-edit   edit XML configuration for a network filter

    pool-autostart  autostart a pool

    pool-build      build a pool

    pool-create     create a pool from an XML file

    pool-create-as  create a pool from a set of args

    pool-define     define (but don't start) a pool from an XML file

    pool-define-as  define a pool from a set of args

    pool-destroy    destroy a pool

    pool-delete     delete a pool

    pool-dumpxml    pool information in XML

    pool-edit       edit XML configuration for a storage pool

    pool-info       storage pool information

    pool-list       list pools

    pool-name       convert a pool UUID to pool name

    pool-refresh    refresh a pool

    pool-start      start a (previously defined) inactive pool

    pool-undefine   undefine an inactive pool

    pool-uuid       convert a pool name to pool UUID

    secret-define   define or modify a secret from an XML file

    secret-dumpxml  secret attributes in XML

    secret-set-value set a secret value

    secret-get-value Output a secret value

    secret-undefine undefine a secret

    secret-list     list secrets

    pwd             print the current directory

    quit            quit this interactive terminal

    exit            quit this interactive terminal

    reboot          reboot a domain

    restore         restore a domain from a saved state in a file

    resume          resume a domain

    save            save a domain state to a file

    schedinfo       show/set scheduler parameters

    dump            dump the core of a domain to a file for analysis

    shutdown        gracefully shutdown a domain

    setmem          change memory allocation

    setmaxmem       change maximum memory limit

    setvcpus        change number of virtual CPUs

    suspend         suspend a domain

    ttyconsole      tty console

    undefine        undefine an inactive domain

    update-device   update device from an XML file

    uri             print the hypervisor canonical URI

    vol-create      create a vol from an XML file

    vol-create-from create a vol, using another volume as input

    vol-create-as   create a volume from a set of args

    vol-clone       clone a volume.

    vol-delete      delete a vol

    vol-wipe        wipe a vol

    vol-dumpxml     vol information in XML

    vol-info        storage vol information

    vol-list        list vols

    vol-pool        returns the storage pool for a given volume key or path

    vol-path        returns the volume path for a given volume name or key

    vol-name        returns the volume name for a given volume key or path

    vol-key         returns the volume key for a given volume name or path

    vcpuinfo        domain vcpu information

    vcpupin         control domain vcpu affinity

    version         show version

    vncdisplay      vnc display

    snapshot-create Create a snapshot

    snapshot-current Get the current snapshot

    snapshot-delete Delete a domain snapshot

    snapshot-dumpxml Dump XML for a domain snapshot

    snapshot-list   List snapshots for a domain

    snapshot-revert Revert a domain to a snapshot

virsh #