How to write in bold using ncurses in C

To use ncurses in your program, you first need to install ncurses. Once installed, write the below code:

#include <ncurses.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  int ch;
  initscr();
  raw();
  keypad(stdscr, TRUE);
  noecho();
  printw("Type any character to see it in bold\n");
  ch = getch();
  if (ch == KEY_F(1))
    printw("F1 Key pressed");
  else {
    printw("The pressed key is ");
    attron(A_BOLD);
    printw("%c", ch);
    attroff(A_BOLD);
  }
  refresh();
  getch();
  endwin();
  return EXIT_SUCCESS;
}

To compile it, use the ncurses library using
$ gcc file.c -lncurses

Once compiled, it will generate a executable named a.out

Type any character to see it in bold

The pressed key is A

If you need any help installing ncurses, write in comment section.

Generating password using openssl for your unix accounts

There is a need when you need to create an account using password hash, follow below steps to simply create password hash.

$ openssl passwd -1
Password: <your pass>
Verifying - Password: <your pass>
Hash will appear here as an output

openssl is the command to generate password
passwd is an argument and -1 represents here that we want unix kind of hash from passwords as an output. There are other options too, like md5, crypt.

For example, you can use:

$ openssl passwd -crypt
or,
$ openssl passwd -md5

You can also provide the salt, to enhance the security

$ openssl passwd -crypt -salt (yourSalt)

This salt is required to decrypt the password.

You can also use python crypt function to create encrypted hashes:


# PASS="strongpass" python -c "import crypt; import os; print crypt.crypt(os.environ['PASS'], 'salt')"&
# ps fauxwww | grep 'python -c'

In this manner, the password will not appear in ps output.

To hide from history, you can disable and enable the history using following option
set +o history
# PASS="strongpass" python -c "import crypt; import os; print crypt.crypt(os.environ['PASS'], 'salt')"&
set -o history

So, go ahead and generate your hashes.

RAINBOW ROSE in shell script

To gift your friend, you can send him/her a rainbow rose by using below shell script

#!/bin/bash
RED='\033[1;31m'
GREEN='\033[1;32m'
CYAN='\033[0;36m'
YELLOW='\033[1;33m'

printf "${RED}    .--.---.\n"
sleep 1;
printf "   ( ${CYAN}\'--'/${RED} )\n"
sleep 1;
printf "  ( ${CYAN}'..-...'${RED} )\n"
sleep 1;
printf "   '.${CYAN}'-._.'${RED}.'\n"
sleep 1;
printf "    <'${CYAN}-.,.${RED}->\n"
sleep 1;
printf "${GREEN}       \`\\(  ${YELLOW}  _\n"
sleep 1;
printf "${GREEN}        < \ ${YELLOW} / \ \n"
sleep 1;
printf "       ${YELLOW}__${GREEN} \\\\\\ $YELLOW|_/\n"
sleep 1;
printf "      /  \ ${GREEN}\\\\\\ \n"
sleep 1;
printf "      ${YELLOW}'--'.${GREEN}\\\\\\ ${YELLOW}>\n"
sleep 1;
printf "${GREEN}            \\\\\\   \n"
printf "\n"
printf "${CYAN}RAI${RED}NBOW${GREEN} ${RED}ROSE${RED} FOR ${CYAN}YOU${CYAN} ${GREEN}MY${YELLOW} FRIEND\n"

And it will look like this:

Understanding Exec

At times, you have noticed that there is a usage of exec in shell scripts. What it actually does, and where to use it exactly?

The command works on the theory of, is "never coming back"

exec command is shell builtin, and other members of the commands are execve, execvp, execv.

1. exec command starts the new process, without forking, so once it starts the new process, the old process get finished.

Case 1:
bash:~$ ps -ef | grep -i bash
csblog  13062 12371  1 15:19 pts/5    00:00:00 bash
ksh$ ksh
ksh$ ps -ef | grep -i ksh
csblog  13093 13062  0 15:19 pts/5    00:00:00 ksh
ksh$ ps -ef | grep -i bash
csblog  13062 12371  0 15:19 pts/5    00:00:00 bash

Case 2:
bash:~$ exec ksh
ksh$ ps -ef | grep -i bash
ksh$ ps -ef | grep -i ksh
csblog  13062 12371  0 15:19 pts/5    00:00:00 ksh

You can see, in case 1, i have started the process, without using exec, so the new shell, is subshell for the old one. But in case of case2, a totally new process is started. In this manner, your resources are saved.

2. Sometimes, you don't need user to access the shell, you can directly change in /etc/passwd, but you need to load the environment, so you can add the exec command, at the end of .profile.

3. exec, also used with file descriptor. To open, close, read and write.

exec 3< thisfile          # open "thisfile" for reading on file descriptor 3
exec 4> thatfile          # open "thatfile" for writing on file descriptor 4
exec 8<> tother           # open "tother" for reading and writing on fd 8
exec 6>> other            # open "other" for appending on file descriptor 6
exec 5<&0                 # copy read file descriptor 0 onto file descriptor 5
exec 7>&4                 # copy write file descriptor 4 onto 7
exec 3<&-                 # close the read file descriptor 3
exec 6>&-                 # close the write file descriptor 6

read <&3
echo stuff >&4


Source: Stackoverflow.com

How to log your mysql queries in Ubuntu 16.04

At times, you need to log your mysql queries.

The first you need to locate your configuration file of mysql. You can use either locate command or the find command for it. The name of the configuration file for mysql is "my.cnf", and in ubuntu its usually present in your /etc directory.

$ find /etc -name "my.cnf"

or

$ locate my.cnf

In my system, it's located in /etc/mysql/my.cnf

Once the file is located, open it using your favorite text editor.
There are chances that the file is not writable by your user, so you need to use sudo to switch your user to root to edit the file.

Open the file and add the lines,

[mysqld]
general_log = on
general_log_file = /var/log/mysql/mysql_query.log

It will add the group as mysqld, and start the logging. The logs will be save in file:

/var/log/mysql/mysql_query.log

Save it and close it.

Then you need to restart your mysql server, to enable the option. Once the mysql service is started, the logging will start.

$ sudo service mysqld restart

Sample log file:

$ cat /var/log/mysql/mysql_query.log
/usr/sbin/mysqld, Version: 5.7.15-0ubuntu0.16.04.1-log ((Ubuntu)). started with:
Tcp port: 3306  Unix socket: /var/run/mysqld/mysqld.sock
Time                                                  Id Command    Argument
2016-10-13T14:02:57.300324Z    3 Connect myuser@localhost on  using Socket
2016-10-13T14:02:57.300563Z    3 Query select @@version_comment limit 1
2016-10-13T14:03:02.895987Z    3 Query SELECT DATABASE()
2016-10-13T14:03:02.896302Z    3 Init DB test
2016-10-13T14:03:02.898415Z    3 Query show databases
2016-10-13T14:03:02.902113Z    3 Query show tables

npm Error: npm ERR! network read ECONNRESET

Node Error:

npm http GET https://registry.npmjs.org/yo
npm http GET https://registry.npmjs.org/yo
npm http GET https://registry.npmjs.org/yo
npm ERR! network read ECONNRESET
npm ERR! network This is most likely not a problem with npm itself
npm ERR! network and is related to network connectivity.
npm ERR! network In most cases you are behind a proxy or have bad network settin
gs.
npm ERR! network
npm ERR! network If you are behind a proxy, please make sure that the
npm ERR! network 'proxy' config is set properly.  See: 'npm help config'

This happened because npm is not able to connect with https. Change the https to http, and it will work.

npm config set registry http://registry.npmjs.org/




Resume a suspended job in linux ubuntu

Source: http://superuser.com/questions/268230/how-can-i-resume-a-stopped-job-in-linux

Handling jobs in linux environment:

The general job control commands in Linux are:

• jobs - list the current jobs
• fg - resume the job that's next in the queue
• fg %[number] - resume job [number]
• bg - Push the next job in the queue into the background
• bg %[number] - Push the job [number] into the background
• kill %[number] - Kill the job numbered [number]
• kill -[signal] %[number] - Send the signal [signal] to job number [number]
• disown %[number] - disown the process(no more terminal will be owner), so command will be alive even after closing the terminal.

That's pretty much all of them. Note the % infront of the job number in the commands - this is what tells kill you're talking about jobs and not processes.