Monitor the progress of mysql import

Mysql command does not have any means of monitoring the progress of sql file import. One method that I found useful in monitoring mysql import, is by using pipeviewer(pv) command. To install pipeviewer in a centos box:

Install epel repository
# yum install epel-release -y

Install pv
# yum install pv -y

To use the pv command to monitor mysql import progress

# pv mydatabase.sql | mysql -u myusername -p mydatabase

You will get progress bar showing how much data has been imported from the sql file to mysql.

Force a mongodb in a replica set to be a primary

There was one situation, where our production mongo server suddenly becomes secondary, causing any write and read to the server to fail. Searching in the mongo documentation, we found an easy solution. Below are the steps.

First step:
Check that your replica is running fine
mongo> rs.status()

Second step:
Freeze all mongo node in the replica that you do not want to be primary for lets say, 120 seconds. Access the mongo shell, and run below command, do this for all nodes that you do not want to be primary
mongo> rs.freeze(120) 

Third step:
Demote the current primary, so that other node that has not been frozen, will take over as primary. Run this in mongo shell, to demote the node from being a primary, for 120 seconds
mongo> rs.stepdown(120)

That's it, run rs.status() again to make sure that your desired server is now a primary.

Reference: https://docs.mongodb.com/manual/tutorial/force-member-to-be-primary/

Use centos repository in RHEL

Get the repository url in your country, by visiting http://mirror-status.centos.org/. In my case, since I am in Malaysia, I chose http://centos.ipserverone.com/centos/

Create a repo file in /etc/yum.repos.d
# cat > /etc/yum.repos.d/centos.repo
[centos]
name=CentOS-7
baseurl=http://centos.ipserverone.com/centos/7/os/x86_64/
enabled=1
gpgcheck=1
gpgkey=http://centos.ipserverone.com/centos/7/os/x86_64/RPM-GPG-KEY-CentOS-7

Press ctrl-d to exit and save

Check whether your new centos repo is listed and ready to be used
# yum repolist

Done

Backup RHEV/RHV/ovirt disk image to external drive

Login to RHV/RHEV/ovirt administrator interface

Search for your VM, lets say I want to search for windows VM

Right click on the VM name, and choose 'Create Snapshot'

Give a proper name, and tick "Save Memory" if you want to save current state of memory as well. Please be warned, that by choosing "Save Memory", the VM will be paused while the snapshooting is in progress. 

If you check the Snapshots tab, the status of the snapshot will be Locked, and the VM will be paused

Once completed, the status will be changed to Ok

Now, open a terminal inside the rhev machine, and search for the disk image snapshot by running below command:

# virsh -r dumpxml windows | grep "source file"

Your newly created snapshot is on the last line of the above command. Copy the file location, and put it into your external drive

# cp /rhev/data-center/00000002-0002-0002-0002-00000000035d/747b7d84-68d5-4436-98f5-baeec68381e1/images/8af6c761-94ac-4adb-bf33-f009e3dd3dc7/../8af6c761-94ac-4adb-bf33-f009e3dd3dc7/../8af6c761-94ac-4adb-bf33-f009e3dd3dc7/../8af6c761-94ac-4adb-bf33-f009e3dd3dc7/../8af6c761-94ac-4adb-bf33-f009e3dd3dc7/e42c8e85-9566-4953-b881-70c7ce97de0b /mnt/my_external_drive/windows-snapshot-20181219.raw

If you want a different format, use qemu-img command to change it. For example, you require this image to be vmware compatible

# qemu-img -f raw -O vmdk /mnt/my_external_drive/windows-snapshot-20181219.raw /mnt/my_external_drive/windows-snapshot-20181219.vmdk

Send postgresql log to syslog

Enable syslog to listen to udp port 514 (the port number can be changed to suit your need)

# vi /etc/rsyslog.conf

$ModLoad imudp

$UDPServerRun 514

Restart rsyslog

# systemctl restart rsyslog

Check if rsyslog is now listening to 514 udp port

# ss -tulpn | grep 514

udp    UNCONN     0      0                      *:514                   *:*      users:(("rsyslogd",15281,3))

udp    UNCONN     0      0                     :::514                  :::*      users:(("rsyslogd",15281,4))

Set postgres to log to syslog

# vi /var/lib/pgsql/9.5/data/postgresql.conf

log_destination = 'syslog'

Restart postgres

# systemctl restart postgresql-9.5

Check if your postgres log is now being logged by syslog

# tail -f /var/log/messages 

...

Dec 11 08:39:21 mypostgres postgres[21518]: [3-1] < 2018-12-11 08:39:21.932 UTC >LOG:  autovacuum launcher started