ubuntu cli / scripting

ubuntu/shell-script.md

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+# shell Programming
+
+* [Tutorial](https://www.tutorialspoint.com/unix/shell_scripting.htm)
+
+```sh
+#!/bin/sh
+
+echo "File Name: $0"
+echo "First Parameter : $1"
+echo "Second Parameter : $2"
+echo "Quoted Values: $@"
+echo "Quoted Values: $*"
+echo "Total Number of Parameters : $#"
+```
+
+
+
+* while loop
+
+```sh
+#!/bin/sh
+
+a=0
+while [ "$a" -lt 10 ]    # this is loop1
+do
+   b="$a"
+   while [ "$b" -ge 0 ]  # this is loop2
+   do
+      echo -n "$b "
+      b=`expr $b - 1`
+   done
+   echo
+   a=`expr $a + 1`
+done
+```
+
+
+
+* Assume variable **a** holds 10 and variable **b** holds 20 then 
+
+| Operator |                         Description                          |          Example           |
+| :------: | :----------------------------------------------------------: | :------------------------: |
+| **-eq**  | Checks if the value of two operands are equal or not; if yes, then the condition becomes true. | [ $a -eq $b ] is not true. |
+| **-ne**  | Checks if the value of two operands are equal or not; if values are not equal, then the condition becomes true. |   [ $a -ne $b ] is true.   |
+| **-gt**  | Checks if the value of left operand is greater than the value of right operand; if yes, then the condition becomes true. | [ $a -gt $b ] is not true. |
+| **-lt**  | Checks if the value of left operand is less than the value of right operand; if yes, then the condition becomes true. |   [ $a -lt $b ] is true.   |
+| **-ge**  | Checks if the value of left operand is greater than or equal to the value of right operand; if yes, then the condition becomes true. | [ $a -ge $b ] is not true. |
+| **-le**  | Checks if the value of left operand is less than or equal to the value of right operand; if yes, then the condition becomes true. |   [ $a -le $b ] is true.   |
+
+
+
+| Operator |                         Description                          |                Example                |
+| :------: | :----------------------------------------------------------: | :-----------------------------------: |
+|  **!**   | This is logical negation. This inverts a true condition into false and vice versa. |         [ ! false ] is true.          |
+|  **-o**  | This is logical **OR**. If one of the operands is true, then the condition becomes true. | [ $a -lt 20 -o $b -gt 100 ] is true.  |
+|  **-a**  | This is logical **AND**. If both the operands are true, then the condition becomes true otherwise false. | [ $a -lt 20 -a $b -gt 100 ] is false. |
+
+* Other [Operator](https://www.tutorialspoint.com/unix/unix-basic-operators.htm)
+

ubuntu/systemctl.md

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+# Quick Guide for auto start service
+
+* [Reference](https://medium.com/@benmorel/creating-a-linux-service-with-systemd-611b5c8b91d6)
+
+* [Reference 2](https://linuxconfig.org/how-to-create-systemd-service-unit-in-linux)
+
+* [DZone](https://dzone.com/articles/run-your-java-application-as-a-service-on-ubuntu)
+
+* create service script in `/etc/systemd/system/myserver.service`
+
+  ```ini
+  [Unit]
+  Description=ROT13 demo service
+  After=network.target
+  StartLimitIntervalSec=0
+  [Service]
+  Type=simple
+  Restart=always
+  RestartSec=1
+  User=centos
+  ExecStart=/usr/bin/env php /path/to/server.php
+  
+  [Install]
+  WantedBy=multi-user.target
+  ```
+
+* sample java application
+
+  ```sh
+  [Unit]
+  Description=My Webapp Java REST Service
+  [Service]
+  User=ubuntu
+  # The configuration file application.properties should be here:
+  
+  #change this to your workspace
+  WorkingDirectory=/home/ubuntu/workspace
+  
+  #path to executable. 
+  #executable is a bash script which calls jar file
+  ExecStart=/home/ubuntu/workspace/my-webapp
+  
+  SuccessExitStatus=143
+  TimeoutStopSec=10
+  Restart=on-failure
+  RestartSec=5
+  
+  [Install]
+  WantedBy=multi-user.target
+  ```
+
+* script `/home/ubuntu/workspace/my-webapp`. Change to executable `sudo chmod u+x my-webapp`
+
+  ```sh
+  #!/bin/sh
+  sudo /usr/bin/java -jar my-webapp-1.0-SNAPSHOT.jar server config.yml
+  ```
+
+  
+
+  
+
+* start service
+
+  ```sh
+  
+  $ sudo systemctl start myserver.service
+  
+  // or 
+  $ sudo systemctl start myserver
+  ```
+
+  
+
+* to restart
+
+  ```sh
+  $ sudo systemctl restart myserver.service
+  ```
+
+  
+
+* automatically start on boot
+
+```sh
+$ sudo systemctl enable myserver.service
+```
+
+* check active
+
+  ```sh
+  $ systemctl is-active myserver.service
+  ```
+
+* All services status
+
+  ```sh
+  $ service  --status-all
+  ```
+
+  
+