create external table with data in csv

 create external table  if not exists my_db.mytable(
  name string,
 age int)
COMMENT 'Example table'
ROW FORMAT DELIMITED
FILEDS TERMINATED BY ','
SOTRED AS TEXTFILE
LOCATION '/data/warehouse/employee_data'
tableproperties("skip.header.line.count"="1")

What is difference between tail -f and tailf in unix?

The tailf just waits almost infinite. But the tail -f begin to print the output within seconds.

I have digged deeper by examining the underlying system calls using strace command. The results given below:

# strace tailf /var/log/messages

(truncated)
stat("/var/log/messages", {st_mode=S_IFREG|0600, st_size=47432599401, ...}) = 0
open("/var/log/messages", O_RDONLY)     = 3
fstat(3, {st_mode=S_IFREG|0600, st_size=47432600425, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f7dba2d1000
read(3, "Nov  1 03:23:01 hostnameXXXX"..., 4096) = 4096
read(3, "0.31.148.12)\nNov  1 03:54:33 del"..., 4096) = 4096
read(3, "io.c(600) [receiver=3.0.6]\nNov  "..., 4096) = 4096
(truncated)

As you can see, the tailf is trying to read (buffer) all the lines from beginning before generating output to the screen.

Check the output of tail -f below, here it is using the system call lseek (C/C++) to directly jump to end of file and start reading from there:

# strace tail -f /var/log/messages

(truncated)
open("/var/log/messages", O_RDONLY)     = 3
fstat(3, {st_mode=S_IFREG|0600, st_size=47294167448, ...}) = 0
lseek(3, 0, SEEK_CUR)                   = 0
lseek(3, 0, SEEK_END)                   = 47294170917
lseek(3, 47294169088, SEEK_SET)         = 47294169088
(truncated)

Connect Android Device to Ubuntu Laptop

 

Step 1: How to Install scrcpy in Ubuntu 18.04.5

Step 2: How to enable USB in Samsung Tablet.

Step A:

Settings

=> About tablet

        => Software Information

                => Build Number => here tab 7 times.. then Developer option will be

enabled.

Step B:

Settings

=>Enable USB Debugging

Step 3: Connect Table to Laptop with USB Cable

Step 4: Now Type the following to connect ti the tablet.

scrcpy --lock-video-orientation 1

Step 5: Increase screen size in scrcpy.

scrcpy 1.13 adds two new options related to orientation: an option to lock the video orientation, and shortcuts to rotate display in steps of 90°.

scrcpy --lock-video-orientation 0 

• 90° counterclockwise:

scrcpy --lock-video-orientation 1

• 180°:

scrcpy --lock-video-orientation 2

• 90° clockwise:

How to To Install Jupyter on Ubuntu 18.04

How to To Install Jupyter on Ubuntu 18.04

How to run Jupyter.

jupyter notebook --allow-root

How to Install OpenCV on Ubuntu 18.04

 

How to Install OpenCV on Ubuntu 18.04

Executing shell script as cronjob

Problem: Executing  shell script as cronjob

Solution:  

Try,

 #!/bin/bash
 /bin/touch file.txt

cron as:

 * * * * * /bin/sh /home/myUser/scripts/test.sh

And you can confirm this by:

 # tailf /var/log/cron

Best tool for Cron learning

crontab