Linux for freshers

Friday, November 4, 2016

How do I display shell command history with date and time under UNIX or Linux operating systems?

If the HISTTIMEFORMAT is set, the time stamp information associated with each history entry is written to the history file, marked with the history comment character. Defining the environment variable as follows

root@linuxforfreshers.com:~$ vim .bash_profile

$ HISTTIMEFORMAT="%d/%m/%y %T "

:wq

root@linuxforfreshers.com:~$ echo 'export HISTTIMEFORMAT="%d/%m/%y %T "' >> ~/.bash_profile

root@linuxforfreshers.com:~$ source .bash_profile

Where,

%d – Day

%m – Month

%y – Year

%T – Time

root@linuxforfreshers.com:~$ history

Sample outputs:

986 10/03/1104:31:36 memcached-tool 10.10.28.22:11211 stats

987 10/03/1104:31:36 w

988 10/03/1104:31:37 iostat

989 10/03/1104:31:37 top

990 10/03/1104:31:37 at

991 10/03/1104:31:38 atop

992 10/03/1104:31:40 collectl

993 10/03/1104:31:41 grep CPU /proc/cpuinfo

994 10/03/1104:31:45 vmstat 3 100

995 10/03/1104:31:55 sar -W -f /var/log/sa/sa12

References:

For more info type the following commands:

man bash

help history

man 3 strftime

Thursday, November 3, 2016

How to check which port number mysql server is running on linux ?

Method 1:

To find a listener on a port, do this:

root@linuxforfreshers.com:~$netstat -tln | grep 3306

tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN

root@linuxforfreshers.com:~$netstat -tlpn | grep mysql

tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 870/mysqld

Method 2:

root@linuxforfreshers.com:~$grep port /etc/mysql/my.cnf

# One can use all long options that the program supports.

# It has been reported that passwords should be enclosed with ticks/quotes

port = 3306

Method 3:

Using Mysql Query

root@linuxforfreshers.com:~$ mysql –u username –p password

mysql> SHOW GLOBAL VARIABLES LIKE 'PORT';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| port | 3306 |

+---------------+-------+

how to check mysql server uptime in linux ?

Method 1:

Using command line

root@linuxforfreshers.com:~$mysqladmin version | grep Uptime

Uptime: 30 sec

Method 2:

root@linuxforfreshers.com:~$mysqladmin status

Uptime: 121 Threads: 1 Questions: 116 Slow queries: 0 Opens: 46 Flush tables: 1 Open tables: 41 Queries per second avg: 0.958

Method 3:

Show MySQL server uptime using a query

root@linuxforfreshers.com:~$ mysql –u username –p password

mysql> SHOW GLOBAL STATUS LIKE 'Uptime';

+---------------+-------+

| Variable_name | Value |

+---------------+-------+

| Uptime | 223 |

+---------------+-------+

(The uptime is given in seconds)

how to check if mysql server is running or not in linux ?

Method 1:

root@linuxforfreshers.com:~$ service mysql status

root@linuxforfreshers.com:~$ /etc/init.d/mysql status

mysql start/running, process 13749

Method 2:

root@linuxforfreshers.com:~$ps aux | grep mysql

mysql 13749 0.2 1.3 492660 52336 ? Ssl 13:05 0:38 /usr/sbin/mysqld

Method 3:

root@linuxforfreshers.com:~$netstat -vulntp |grep -i mysql

tcp 0 0 127.0.0.1:3306 0.0.0.0:* LISTEN 13749/mysqld

Method 4:

root@linuxforfreshers.com:~$lsof -i :3306

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME

mysqld 13749 mysql 10u IPv4 5037327 0t0 TCP localhost:mysql (LISTEN)

Method 5:

root@linuxforfreshers.com:~$mysqladmin ping

mysqld is alive

Tuesday, October 4, 2016

who command examples in linux ?

You need to use who command to display users who are currently logged in your server

Purpose

Display who is on the system

Syntax

The basic syntax is as follows:

who

who am i

who [options] [File]

who --help

who --version

who | grep 'userNameHere'

who command examples

To show a list of all the users currently logged in to the system, type:

$ who

root@linuxforfreshers.com:~$ who

root :0 2016-10-03 07:46 (:0)

root pts/61 2016-10-04 08:08 (:0)

root pts/46 2016-10-04 07:58 (:0)

To show only hostname and user associated with stdin (usually keyboard), enter:

$ who -m

root@linuxforfreshers.com:~$ who -m

root pts/61 2016-10-04 08:08 (:0)

To show active processes spawned by init:

$ who -p

To show user’s message status as +, – or ?, enter:

$ who -T

root@linuxforfreshers.com:~$ who -T

root ? :0 2016-10-03 07:46 (:0)

root + pts/61 2016-10-04 08:08 (:0)

root + pts/46 2016-10-04 07:58 (:0)

Show or list users logged in

Type the command:

$ who -u

root@linuxforfreshers.com:~$ who -u

root :0 2016-10-03 07:46 ? 3431 (:0)

root pts/61 2016-10-04 08:08 . 21700 (:0)

root pts/46 2016-10-04 07:58 01:46 21700 (:0)

Show time of last system boot

To display time of last system boot pass the -b option to who command:

$ who -b

root@linuxforfreshers.com:~$ who -b

system boot 2016-10-03 07:44

Show dead processes on the system

You need pass the -d option to who command:

$ who -d

$ who -d -H

root@linuxforfreshers.com:~$ who -d

pts/9 2016-10-03 16:56 0 id=/9 term=0 exit=0

pts/58 2016-10-03 16:56 0 id=/58 term=0 exit=0

pts/0 2016-10-03 16:56 0 id=/0 term=0 exit=0

pts/60 2016-10-04 15:55 0 id=/60 term=0 exit=0

pts/62 2016-10-04 15:55 0 id=/62 term=0 exit=0

Show system login processes

To just display system login processes pass the -l option:

$ who -l

$ who -l -H

root@linuxforfreshers.com:~$ who -l

Count all login names and number of users logged on the system

To count all login names and number of users logged on:

$ who -q

root@linuxforfreshers.com:~$ who -q

root root root

# users=3

Display the current runlevel

To display the current system runlevel, type:

$ who -r

root@linuxforfreshers.com:~$ who -r

run-level 2 2016-10-03 07:44

You can combine -r and -b options as follows:

$ who -r -b

root@linuxforfreshers.com:~$ who -r -b

system boot 2016-10-03 07:44

run-level 2 2016-10-03 07:44

root@linuxforfreshers.com:~$ who am i

root pts/61 2016-10-04 08:08 (:0)

Displays "all" information, and headers above each column of data, for example:

root@linuxforfreshers.com:~$ who -aH

NAME LINE TIME IDLE PID COMMENT EXIT

system boot 2016-10-03 07:44

run-level 2 2016-10-03 07:44

root ? :0 2016-10-03 07:46 ? 3431 (:0)

pts/9 2016-10-03 16:56 0 id=/9 term=0 exit=0

pts/58 2016-10-03 16:56 0 id=/58 term=0 exit=0

root + pts/61 2016-10-04 08:08 . 21700 (:0)

pts/0 2016-10-03 16:56 0 id=/0 term=0 exit=0

root + pts/46 2016-10-04 07:58 01:39 21700 (:0)

pts/60 2016-10-04 15:55 0 id=/60 term=0 exit=0

pts/62 2016-10-04 15:55 0 id=/62 term=0 exit=0