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Configure NTP in ESXi from the command line

Display NTP settings

~ # cat /etc/ntp.conf
restrict 127.0.0.1
restrict default kod nomodify notrap
driftfile /etc/ntp.drift
~ # This is a freshly installed server and there's no ntp server configured.

Configure NTP server

We will use NTP Pool Project servers.

    ~ # vi /etc/ntp.conf
    ~ # cat /etc/ntp.conf
    restrict 127.0.0.1
    restrict default kod nomodify notrap
    server 0.pool.ntp.org
    server 1.pool.ntp.org
    driftfile /etc/ntp.drift
    ~ #

Restart NTP

~ # /etc/init.d/ntpd restart
Stopping ntpd
Starting ntpd
~ #

Display NTP peers

~ # ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 ns02.hns.net.in .INIT.          16 u    -   64    0    0.000    0.000   0.000
 123.108.200.124 .INIT.          16 u    -   64    0    0.000    0.000   0.000
~ #

It could take sometime to sync.

    ~ # ntpq -p
         remote           refid      st t when poll reach   delay   offset  jitter
    ==============================================================================
    +123.108.200.124 103.252.195.20   3 u   46   64  377   81.459    4.968   3.615
    *web10.hnshostin 158.43.128.33    2 u   44   64  377   38.879    5.120   5.157
    ~ #

Enable NTP service

    ~ # chkconfig ntpd on
    ~ # chkconfig --list | grep ntpd
    ntpd                            on
    ~ #

Replace NTP server

sed -i 's/ntpserver/newntpserver/' /etc/ntp.conf

Remove NTP server

sed -i 's/ntpserver//' /etc/ntp.conf

Remove blank lines in ntp.conf

~ # sed -i  '/^\s*$/d' /etc/ntp.conf

Replace ntp.conf with new settings

~ # cat <<EOF > /etc/ntp.conf
> restrict 127.0.0.1
> restrict default kod nomodify notrap
> server 0.pool.ntp.org
> server 1.pool.ntp.org
> driftfile /etc/ntp.drift
> EOF
~ # cat /etc/ntp.conf
restrict 127.0.0.1
restrict default kod nomodify notrap
server 0.pool.ntp.org
server 1.pool.ntp.org
driftfile /etc/ntp.drift
~ #

Run the commands over ssh

    ssh root@servername "command_to_run"

Repeat the commands for multiple hosts over ssh 

    cat > server_list
    Paste the list of servers
    Ctrl+D
    
    for i in `cat server_list`
    do
    ssh root@$i  "command_to_run"
    done