Troubleshooting related tutorial/FAQ

Systemd systemctl list all failed units/services on Linux

last updated April 20, 2020 in CentOS, Debian / Ubuntu, Linux, RedHat and Friends, Suse, Troubleshooting

Is there is a command to print list all failed units or services when using systemd on Linux? Can you tell me the systemctl command to show failed services on Linux?

Remove Santa Hat in VLC Player Permanently

last updated December 20, 2019 in Linux, Mac OS X, Troubleshooting, UNIX, Windows

How do I remove Santa Hat in VLC media player that displayed during Christmas time during 18th December to 1st January?

How to test and validate DNSSEC using dig command line

last updated December 11, 2019 in Linux, Networking, Troubleshooting, UNIX

How do I test and validate DNSSEC using the dig command line under Linux, macOS, *BSD, and Unix-like systems?

How to check hard drive health on FreeBSD

last updated May 20, 2019 in FreeBSD, Hardware, Troubleshooting, UNIX

How do I read my hard disk/SSD health using smartctl command on FreeBSD operating system? How can I hard drive health on FreeBSD and find out if my disk is dying?

Perl: warning: Setting locale failed in Debian and Ubuntu

last updated March 4, 2019 in Debian / Ubuntu, Linux, Troubleshooting

I am trying to install package and doing some other work. But, getting the error that read as “perl: warning: Setting locale failed. perl: warning: Please check that your locale settings:” How do I fix this problem on my Debian Linux server?

FreeBSD wget cannot verify certificate, issued by Let’s Encrypt

last updated December 17, 2018 in FreeBSD, FreeBSD Jails (VPS), Troubleshooting, UNIX

I installed GNU wget utility on FreeBSD as explained here. However, whenever I use the wget command to download stuff from the Internet, it says:
ERROR: cannot verify download.freebsd.org’s certificate, issued by ‘CN=Let\’s Encrypt Authority X3,O=Let\’s Encrypt,C=US’:
Unable to locally verify the issuer’s authority.
How do I fix this problem on FreeBSD 12?

pfSense email notification when fallback WAN connection goes down

last updated December 23, 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?

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