Though timesyncd is fine for most purposes, some applications that are very sensitive to even the slightest perturbations in time may be better served by ntpd, as it uses more sophisticated techniques to constantly and gradually keep the system time on track.
sudo timedatectl set-ntp no
timedatectl
sudo apt-get install ntp
sudo ntpq -p
References
https://www.digitalocean.com/community/tutorials/how-to-set-up-time-synchronization-on-ubuntu-16-04
nohup my_command > my.log 2>&1 & echo $! > save_pid.txt
kill -9 `cat save_pid.txt` rm save_pid.txt
References
https://stackoverflow.com/questions/17385794/how-to-get-the-process-id-to-kill-a-nohup-process
/etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu bionic universe multiverse deb-src http://archive.ubuntu.com/ubuntu bionic universe multiverse deb http://us.archive.ubuntu.com/ubuntu/ bionic universe deb-src http://us.archive.ubuntu.com/ubuntu/ bionic universe deb http://us.archive.ubuntu.com/ubuntu/ bionic-updates universe deb-src http://us.archive.ubuntu.com/ubuntu/ bionic-updates universe deb http://us.archive.ubuntu.com/ubuntu/ bionic multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ bionic multiverse deb http://us.archive.ubuntu.com/ubuntu/ bionic-updates multiverse deb-src http://us.archive.ubuntu.com/ubuntu/ bionic-updates multiverse deb http://security.ubuntu.com/ubuntu bionic-security universe deb-src http://security.ubuntu.com/ubuntu bionic-security universe deb http://security.ubuntu.com/ubuntu bionic-security multiverse deb-src http://security.ubuntu.com/ubuntu bionic-security multiverse
References
https://help.ubuntu.com/lts/serverguide/configuration.html.en
Spring Boot 1.x
jar {
baseName = 'interface'
version = '0.0.1-SNAPSHOT'
manifest {
attributes 'Main-Class': 'net.pupli.sobhan.SobhanApplication'
}
}
Spring Boot 2.x
springBoot {
mainClassName = 'org.baeldung.DemoApplication'
}
or
bootJar {
mainClassName = 'org.baeldung.DemoApplication'
}
bootJar {
manifest {
attributes 'Start-Class': 'org.baeldung.DemoApplication'
}
}
References
In Boot 2.x, the bootJar and bootWar tasks are responsible for packaging the application.
bootJar {
baseName = 'gs-spring-boot'
version = '0.1.0'
}
References
https://spring.io/guides/gs/spring-boot/
https://www.baeldung.com/spring-boot-gradle-plugin
https://www.baeldung.com/spring-boot-main-class
timedatectl list-timezones
sudo timedatectl set-timezone Asia/Tehran
Check if time is correct :
date
References
https://linuxconfig.org/how-to-change-timezone-on-ubuntu-18-04-bionic-beaver-linux
https://www.cyberciti.biz/faq/howto-set-date-time-from-linux-command-prompt/
sudo vim /etc/netplan/01-netcfg.yaml
network:
ethernets:
eno1:
addresses:
- 172.20.63.234/24
- 192.168.10.20/24
- 192.168.1.240/24
dhcp4: false
gateway4: 172.20.63.254
nameservers:
addresses:
- 8.8.8.8
- 8.8.4.4
search: []
enp3s0:
addresses: []
dhcp4: true
optional: true
version: 2
References
Create the RSA Key Pair
ssh-keygen
Copy the Public Key to Ubuntu Server
cat ~/.ssh/id_rsa.pub | ssh username@remote_host "mkdir -p ~/.ssh && touch ~/.ssh/authorized_keys && chmod -R go= ~/.ssh && cat >> ~/.ssh/authorized_keys"
or Copying Public Key Manually
To display the content of your id_rsa.pub key, type this into your local computer:
cat ~/.ssh/id_rsa.pub
You will see the key’s content, which should look something like this:
ssh-rsa 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 demo@test
make sure the ~/.ssh directory exists.This command will create the directory if necessary, or do nothing if it already exists:
mkdir -p ~/.ssh
Now, you can create or modify the authorized_keys file within this directory. You can add the contents of your id_rsa.pub file to the end of the authorized_keys file, creating it if necessary, using this command:
echo public_key_string >> ~/.ssh/authorized_keys
Finally, we’ll ensure that the ~/.ssh directory and authorized_keys file have the appropriate permissions set:
chmod -R go= ~/.ssh
Authenticate to Ubuntu Server Using SSH Keys
ssh username@remote_host
Disable Password Authentication on your Server
sudo nano /etc/ssh/sshd_config
PasswordAuthentication no
sudo systemctl restart ssh
References
https://www.digitalocean.com/community/tutorials/how-to-set-up-ssh-keys-on-ubuntu-1604
cd /usr/local/openvpn_as/scripts
View current cipher configuration keys
./sacli ConfigQuery | grep "cipher"
Set the cipher configuration key to the desired cipher:
./sacli --key "vpn.client.cipher" --value AES-128-CBC ConfigPut ./sacli --key "vpn.server.cipher" --value AES-128-CBC ConfigPut ./sacli start
References
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String s1 = sc.next();
int x = sc.nextInt();
PadLeft(s1);
System.out.printf("%03d", x);
System.out.println();
PadRight(s1);
System.out.printf("%03d", x);
}
private static void PadRight(String s)
{
System.out.printf("%1$15s", s);
}
private static void PadLeft(String s)
{
System.out.printf("%1$-15s", s);
}
15 represents the minimal width of the String
Input
Hello 12
Output
Hello 012
Hello012
References
https://stackoverflow.com/questions/13475388/generate-fixed-length-strings-filled-with-whitespaces
http://www.rgagnon.com/javadetails/java-0448.html