Convert Joda-Time `DateTime` with timezone

DateTime dateTimePlus2 = DateTime.parse("2015-07-09T05:10:00+02:00");
System.out.println(dateTimePlus2);

DateTime dateTimeUTC = dateTimePlus2.withZone(DateTimeZone.UTC);
System.out.println(dateTimeUTC);

LocalDateTime localDateTimeUTC = dateTimeUTC.toLocalDateTime();
System.out.println(localDateTimeUTC);

References
https://stackoverflow.com/questions/27381626/convert-joda-time-datetime-with-timezone-to-datetime-without-timezone
https://stackoverflow.com/questions/23939576/how-to-specify-a-timezone-for-a-joda-datetime-object

Returning Image/Media Data with Spring

@RequestMapping(value = "/image-manual-response", method = RequestMethod.GET)
public void getImageAsByteArray(HttpServletResponse response) throws IOException {
    InputStream in = servletContext.getResourceAsStream("/WEB-INF/images/image-example.jpg");
    response.setContentType(MediaType.IMAGE_JPEG_VALUE);
    IOUtils.copy(in, response.getOutputStream());
}

or

@GetMapping(
  value = "/get-image-with-media-type",
  produces = MediaType.IMAGE_JPEG_VALUE
)
public @ResponseBody byte[] getImageWithMediaType() throws IOException {
    InputStream in = getClass()
      .getResourceAsStream("/com/baeldung/produceimage/image.jpg");
    return IOUtils.toByteArray(in);
}

References
https://www.baeldung.com/spring-mvc-image-media-data
https://www.baeldung.com/spring-controller-return-image-file

Make iptables rules persistent after reboot on Ubuntu 18.04

sudo apt install iptables-persistent netfilter-persistent

systemctl enable netfilter-persistent
netfilter-persistent save
netfilter-persistent start

iptables-save  > /etc/iptables/rules.v4
ip6tables-save > /etc/iptables/rules.v6

iptables-restore  < /etc/iptables/rules.v4
ip6tables-restore < /etc/iptables/rules.v6

systemctl stop    netfilter-persistent
systemctl start   netfilter-persistent
systemctl restart netfilter-persistent

Remove persistent iptables rules

To remove persistent iptables rules simply open a relevant /etc/iptables/rules.v* file and delete lines containing all unwanted rules.

References
https://askubuntu.com/questions/1052919/iptables-reload-restart-on-ubuntu-18-04
https://linuxconfig.org/how-to-make-iptables-rules-persistent-after-reboot-on-linux

Install NVIDIA (non-free) on Manjaro

Install NVIDIA Drivers

sudo mhwd -a pci nonfree 0300

Configure The Resolution/Refresh Rate

sudo nvidia-settings

Save to X Configuration File button and save to /etc/X11/mhwd.d/nvidia.conf

sudo mhwd-gpu --setmod nvidia --setxorg /etc/X11/mhwd.d/nvidia.conf

Configure X Screen settings (OpenGL Settings, Antialiasing, X Server XVideo)

Troubleshooting: X-Server Failed to Start and Install

sudo mhwd -r pci video-nvidia

Reboot your computer

sudo gedit /etc/mkinitcpio.conf

delete the word nouveau from the following line:

MODULES=" nouveau" 

# sudo mkinitcpio -p [linux kernel version]
sudo mkinitcpio -p linux419
sudo mhwd -a pci nonfree 0300

References
https://wiki.manjaro.org/index.php?title=Configure_NVIDIA_(non-free)_settings_and_load_them_on_Startup

Set Permanently ulimit -n / open files in ubuntu

The currently configured system max can be seen with the command

cat /proc/sys/fs/file-max

This value is the total for the system, not per process.

# available limit
user@ubuntu:~$ ulimit -n
1024

# To increase the available limit to say 65535
user@ubuntu:~$ sudo vim /etc/sysctl.conf

# add the following line to it
fs.file-max = 65535

# run this to refresh with new config
user@ubuntu:~$ sudo sysctl -p
# edit the following file
user@ubuntu:~$ sudo vim /etc/security/limits.conf

# add following lines to it
* soft     nproc          65535    
* hard     nproc          65535   
* soft     nofile         65535   
* hard     nofile         65535
root soft     nproc          65535    
root hard     nproc          65535   
root soft     nofile         65535   
root hard     nofile         65535

# edit the following file
user@ubuntu:~$ sudo vim /etc/pam.d/common-session
# fedora => /etc/pam.d/login

# add this line to it
session required pam_limits.so

# logout and login and try the following command
user@ubuntu:~$ ulimit -n
65535

References
https://medium.com/@muhammadtriwibowo/set-permanently-ulimit-n-open-files-in-ubuntu-4d61064429a
https://askubuntu.com/questions/1110544/what-is-the-maximum-recommended-number-of-open-file-descriptors-on-my-vmware-whi