Troubleshooting related tutorial/FAQ

pfSense email notification when fallback WAN connection goes down

last updated August 1, 2018 in FreeBSD, Monitoring, Troubleshooting, UNIX

I have two WAN connection. The first WAN connection connects via FTTH modem. The second connection connects via 4G LTE CPE modem. I have configured fallback and load balanced dual WAN connection on my pfSense box. However, once in while the Internet connection either one of the WAN goes down. How can I tell pfSense to send an email notification when fallback (or any) WAN connection goes down? How to configure pfSense email notification when an alert happens?

Slow performance issues of OpenBSD or FreeBSD KVM guest on Linux

last updated July 22, 2018 in CentOS, Linux KVM, RedHat and Friends, Troubleshooting

I run a couple of OpenBSD and FreeBSD guest/virtual machines under KVM. My server has 32GB ram and 4C/8T Intel Xeon CPU. Everything was working fine until recent CentOS Linux 7 kernel update. After a fresh reboot of my CentOS 7 Linux box OpenBSD and FreeBSD machine become very slow and after 24 hours stop responding to the network request. How can I solve significant performance problems with BSD family of oses running on CentOS 7 KVM?

How to redirect Nginx non-www to www domain over SSL

last updated April 24, 2018 in Linux, Nginx, Troubleshooting, UNIX

I am getting an error that reads, “Your connection is not secure” when trying to redirect https://theos.in/ to https://www.theos.in/ domain using HTTP 301. How do I redirect Nginx non-www to www domain over SSL?

How to reset forgotten root password for Linux KVM qcow2 image/vm

last updated February 10, 2018 in Debian / Ubuntu, Linux, Linux KVM, Troubleshooting

I have Debian Linux VM running on KVM. I think I forgotten the password for the root account and I am no longer able to run ‘su -‘ command. How do I reset the password for the root account for KVM VM which is in qcow2 format?
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How to use/run bash aliases over ssh based session

last updated December 26, 2017 in BASH Shell, Linux, OpenBSD, Troubleshooting, UNIX

I have set up a bash alias named file_repl. It works entirely when I log in using ssh command. However, my bash aliases are not running over ssh, for example:
$ ssh vivek@server1.cyberciti.biz file_repl bash: file_repl: command not found
How do I run bash shell aliases when I use ssh command?

Fix Host ‘IP’ is blocked because of many connection errors on MySQL/MariaDB

last updated November 15, 2017 in CentOS, Debian / Ubuntu, FreeBSD, Linux, MySQL, Suse, Troubleshooting, UNIX

I am trying to login to my mysql/mysqld server using the following Unix command:
$ mysql -u foo -h 172.16.5.100 -p dbnmame
But greeted with the following error on screen:
ERROR 1129 (HY000): Host ‘172.16.5.100’ is blocked because of many connection errors; unblock with ‘mysqladmin flush-hosts’
How do I fix this problem on a Linux or Unix-like system?

Ubuntu: /dev/xvda2 should be checked for errors

last updated June 16, 2017 in Amazon Cloud Computing, Debian / Ubuntu, Hardware, Linux, Troubleshooting, Ubuntu Linux

When I log in to my Ubuntu Linux 16.04 LTS AWS cloud server, I get the message on screen: /dev/xvda2 should be checked for errors. I can not run fsck command on /dev/xvda1 because it is mounted. How do I check my disk for error without corrupting data?

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