Multipath command with an examples

In linux operating system device mapping through multipath is widely used. Here, we can give you some example how we will use the multipath commands in Linux server

➤ Normally multipath device has a Word Wide Identifier (WWID), which is globally unique and unchanging.

➤ When new devices are brought under the control of DM-Multipath, the new devices may be seen in three different places under the /dev directory: /dev/mapper/mpathn, /dev/mpath/mpathn, and /dev/dm-n

➤ The devices in /dev/mapper are created early in the boot process. Use these devices to access the multipathed devices, for example when creating logical volumes.
The devices in /dev/mpath are provided as a convenience so that all multipathed devices can be seen in one directory. These devices are created by the udev device manager and may not be available on startup when the system needs to access them.

Note: Do not use these devices for creating logical volumes or filesystems

➤ Any devices of the form /dev/dm-n are for internal use only and should never be used.

Please find the multipath syntax which we used in the Linux operating system.


l    -> Display the current multipath configuration gathered from sysfs and the device mapper.

ll  -> Display the current multipath configuration gathered from sysfs, the device mapper, and all other available components on the system.

f    -> Remove the named multipath device.

F   -> Remove all unused multipath devices.

v   ->  Verbosity level
          . 0 no output
          . 1 print created devmap names only
          . 2 default verbosity
          . 3 print debug information

d   -> Dry run, do not create or update devmaps

r    -> Force devmap reload

⧪ How to display the current multipath configuration with all information.

[root@localhost~]# multipath -ll
Dec 21 11:27:17 | multipath.conf line 35, invalid keyword: selector
mpathf (3600c0ff00019e9e9dc94c25801000000) dm-6 HP,MSA 2040 SAN
size=466G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=70 status=active
  |- 1:0:0:4 sdg 8:96 active ready running
  |- 2:0:0:4 sdj 8:144 active ready running
  |- 1:0:1:4 sdq 65:0 active ready running
  `- 2:0:1:4 sdt 65:48 active ready running

⧪ How to remove multipath devices with multipath Command

[root@localhost~]# multipath -f mpathf

Note: if we use -F option then it is remove all unused devices.

⧪ How to Force reload device map with multipath Command

[root@localhost~]# multipath -r

How to check number of CPU and processor in linux operating system

In this post, we will find all the command using which we can find that how many CPU and processor are used in Linux operating system.

⇾ This command are applicable in both RedHat & CentOS operating machine.

➤ How to check number of processor on operating system.

      cat /proc/cpuinfo | grep "physical id" | sort -u | wc -l

   Using above command it show you the number of processor which are currently used on server.

➤ How to check number of cores on Linux operating system.

     cat /proc/cpuinfo | grep "core id" | sort -u | wc -l

➤ You can used other command as well like "lscpu" to check number of processor and core per socket.

➤ Please find the other command which are also used to check the number of processor and cores in  Linux operating system.

    cat /proc/cpuinfo | grep 'model name' | uniq
   cat /proc/cpuinfo | grep "physical id" | sort -u | wc -l
   cat /proc/cpuinfo | grep "core id" | sort -u | wc -l

Useful SQL command for MySQL database on Linux Operating System

This post related to MySQL database SQL command which is used in daily database work by database administrator.

Please find the below points which is very useful to database admin on Linux operating system.

➤ How to create new database:

 CREATE DATABASE <DATABASENAME>;

 e.g. CREATE DATABASE XYZ;

In this example I have created the "XYZ" named database, you can replace database name according to your choice.

➤ How to create mater user with all level access to all available databases:

 GRANT ALL ON *.* TO <USERNAME> IDENTIFIED BY '<PASSWORD>';
 e.g.  GRANT ALL ON *.* TO TESTDBUSER IDENTIFIED BY 'TESTDBUSER';

In this example I used "testdbuser" MySQL user on the server.

➤ How to take backup (dump) of a database:

For this command you need not to login into the database. Once you login on the database please run the below command to take a dump of server.

 mysqldump --lock-all-tables -u <USERNAME> -p -h <DATABASESERVERNAME/IP ADDRESS> <DATABASENAME> > <NEWDUMPFILENAME>.sql

 e.g. mysqldump --lock-all-tables -u ABC -p -h MACHINE1 XYZ > XYZ_16022017.sql

After this command you have to provide DB password only and dump will be done in the folder in which u are working currently.

➤ How to take backup (dump) of a table's:

For this command you need not to login into the database.

 mysqldump -u <USERNAME> -p <DATABASENAME> <TABLENAME> > <NEWDUMPFILENAME>.sql

 e.g. mysqldump -u testdbuser -p testdb test_book > test.sql

After this command you have to provide DB password only and dump will be done in the folder in which u are working currently. for dumping multiple table use space between the table names.

➤ How to run a database dump to another machine:

Go to the folder in which sql dump file is placed and then connect with your Database in which you want to run dump and then run below command.

 source <FILENAME>.sql;

 e.g source XYZ_16022017.sql;

➤ How to take dump only triggers and procedure from database:

 mysqldump --routines --no-create-info --no-data --no-create-db --skip-opt -u <USERNAME> -p <DATABASENAME> > <NEWDUMPFILENAME>.sql

 e.g. mysqldump --routines --no-create-info --no-data --no-create-db --skip-opt -u TESTDBSUER -p XYZ > XYZ_16022017.sql

After this command you have to provide DB password only and dump will be done in the folder in which u are working currently.

➤ How to show procedure/function code:

 SHOW CREATE PROCEDURE <STORED PROCEDURE/FUNCTION NAME>\G

 e.g. SHOW CREATE PROCEDURE FLIGHT_INVOICETOSAP\G;

How to increase filed width of a table attribute:

 ALTER TABLE <TABLENAME> CHANGE <EXISTING_FIELD_NAME> <NEW_FIELD_NAME> <DATATYPE>(<NEW_FIELD_WIDTH>);

 e.g. ALTER TABLE TRILOK CHANGE PASSENGER_NO PASSENGER_NUMBER VARCHAR(30);

field name and data type change is not recommended.

➤ How to display all existing databases:

 SHOW DATABASES;

Using this command you can show all the created database list on the Linux server.

How to display all existing tables:

 SHOW TABLES;
 SHOW TABLES LIKE '<CHARACTERS>%';

Using this command you can check all the tables which is created on the database.

➤ How to recover a MySQL root password:

This is one of the best way to recover the MySQL root password if you forget. I always used below method to reset the root password.
Stop the MySQL server process.

  # /etc/init.d/mysql stop
Start again with no grant tables.

  # mysqld_safe --skip-grant-tables &
Login to MySQL as root. Set new password.

  # mysql -u root
  mysql> use mysql;
  mysql> update user set password=PASSWORD("newrootpassword") where User='root';
  mysql> flush privileges;
  mysql> quit
Exit MySQL and restart MySQL server.

  # /etc/init.d/mysql stop
  # /etc/init.d/mysql start
Set a root password if there is on root password.

  # mysqladmin -u root password newpassword
Update a root password.

  # mysqladmin -u root -p oldpassword newpassword

➤ How to grant privileges to a user:

If we need to provide the privileges to user we will use below two method. I will describe the step by step method for this one.

METHOD 1

Allow the user "bob" to connect to the server from localhost using the password "passwd". Login as root. Switch to the MySQL db. Give privs. Update privs.

  # mysql -u root -p
  mysql> use mysql;
  mysql> grant usage on *.* to bob@localhost identified by 'passwd';
  mysql> flush privileges;

Give user privileges for a db. Login as root. Switch to the MySQL db. Grant privs. Update privs.

  # mysql -u root -p
  mysql> use mysql;
  mysql>INSERT INTO user (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,Create_priv,Drop_priv) VALUES ('%','databasename','username','Y','Y','Y','Y','Y','N');
  mysql> flush privileges;

METHOD 2

  mysql> grant all privileges on databasename.* to username@localhost;
  mysql> flush privileges;

To update info already in a table.

Load a CSV file into a table:

 mysql> LOAD DATA INFILE '/tmp/filename.csv' replace INTO TABLE [table name] FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' (field1,field2,field3);

➤ Dump all databases for backup:

Backup file is SQL commands to recreate all databases.

  # [mysql dir]/bin/mysqldump -u root -ppassword --opt >/tmp/alldatabases.sql

Dump one database for backup.

  # [mysql dir]/bin/mysqldump -u username -p password --databases databasename >/tmp/databasename.sql

Dump a table from a database.

  # [mysql dir]/bin/mysqldump -c -u username -p password databasename tablename > /tmp/databasename.tablename.sql

➤ Restore database (or database table) from backup.

  # [mysql dir]/bin/mysql -u username -p password databasename < /tmp/databasename.sql
  Create Table Example 1.

Using above method we can take database back very fast. I hope through this post you can easily able to create MySQL database, MySQL dump, table creation etc work.

How to mount CIFS file system on Linux Operating Server

Step by Step method for Mount CIFS on Linux Server:

➤ In the initial step we will gather all rpm's or packages information which is required for CIFS file system.

[root@localhost]# rpm -qa | grep cifs 

cifs-utils-4.8.1-20.el6.x86_64

if you see the above output, this packages is required for CIFS file system on Linux system. So you can install this rpm using rpm command if you have rpm packages on the server otherwise you will install the packages using YUM utility.

[root@localhost]#rpm -ivh cifs-utils-4.8.1-20.el6.x86_64.rpm

if you are using YUM, then please install the packages using below command.

[root@localhost]#yum install cifs-utils*

it is installed all required dependency related to CIFS file system.

➤ In this step, we will create the mount point on the server where we need to mount the CIFS file system.

[root@localhost]# mkdir -p /backup/cifs

We will create the above mount directory where i will mount the file system.

➤ Now, we will create a CIFS user and assign a password so the user can access mount folder.

[root@localhost]# touch /etc/cifspasswd

[root@localhost]# chmod 600 /etc/cifspasswd

[root@localhost]#vi /etc/cifspasswd

user=castwebsvc

password=*******

➤ In this step we need to make a permanent entry of mounted file system so once we reboot the machine mounted file system not umount.

[root@localhost]# vi /etc/fstab

ADD fstab entry :

//WindowsServer/share /mount/point cifs rw,mand,user=USER,password=PASS 0 0

Example :

//192.168.0.1/CAST_data4/AICCodeUpload  /backup/cifs cifs   rw,mand,credentials=/etc/cifspasswd         0 0

You can take an example for your system. Please change the mount point as per your requirement.

➤ In the final step you need to mount the file system using below command.

[root@localhost]# mount /backup/cifs

[root@localhost]# mount -a

Using above command the CIFS file system has been mounted successfully.

Remotely shutdown Linux & windows machine using shell script

Please find the below script for shutdown the Unix & Windows server remotely.

#!/bin/bash

 SSH=/usr/bin/ssh
 POWERCMD="/sbin/shutdown -h now"
 HOSTS="server1 server2 server3"

 # Shutdown remote machines
 for i in $HOSTS;
 do
   $SSH -l root $i $POWERCMD;
 done

  telnet=/usr/bin/telnet
  POWER="C:\Windows\System32\shutdown.exe \s"
  IP="server1 server2 server3"

  # Shutdown window machine
  for i in $IP;
  do
        $telnet -l administrator $i $POWER;
  done

 # Shutdown ourself
 /sbin/shutdown -h now

How to mount CIFS file system on Linux Operating server machine

Generally on linux or Unix operating system servers when we are mounting the any other linux machine folder is quite easiy in comparision to mount the window shared folder on linux machine.

Step by Step method for Mount CIFS on Linux Server:
 

➤ In the initial step we will gather all rpm's or packages information which is required for CIFS file system.

[root@localhost]# rpm -qa | grep cifs
cifs-utils-4.8.1-20.el6.x86_64

if you see the above output, this packages is required for CIFS file system on Linux system. So you can install this rpm using rpm command if you have rpm packages on the server otherwise you will install the packages using YUM utility.

[root@localhost]# rpm -ivh cifs-utils-4.8.1-20.el6.x86_64.rpm

if you are using YUM, then please install the packages using below command.

[root@localhost]# yum install cifs-utils*

it is installed all required dependency related to CIFS file system.
 

➤ In this step, we will create the mount point on the server where we need to mount the CIFS file system.

[root@localhost]# mkdir -p /backup/cifs

We will create the above mount directory where i will mount the file system.
 

➤ Now, we will create a CIFS user and assign a password so the user can access mount folder.

[root@localhost]# touch /etc/cifspasswd
[root@localhost]# chmod 600 /etc/cifspasswd

[root@localhost]# vi /etc/cifspasswd

user=castwebsvc
password=*******
 

➤ In this step we need to make a permanent entry of mounted file system so once we reboot the machine mounted file system not umount.

[root@localhost]# vi /etc/fstab

ADD fstab entry :

//WindowsServer/share /mount/point cifs rw,mand,user=USER,password=PASS 0 0

Example :
//192.168.0.1/CAST_data4/AICCodeUpload  /backup/cifs cifs   rw,mand,credentials=/etc/cifspasswd         0 0

You can take an example for your system. Please change the mount point as per your requirement.
 

➤ In the final step you need to mount the file system using below command.

[root@localhost]# mount /backup/cifs
[root@localhost]# mount -a

Using above command the CIFS file system has been mounted successfully

How To Fix “Device eth0 does not seem to be present, delaying initialization” Error

This Ethernet card error is normally occur on Linux operating system like CentOS, Red Hat Linux etc. When you try to up the Ethernet card it is showing you the above topic error.

So in this post, we will provide you the step by step solutions and troubleshoot all the issue related this error.

In the initial step, you will check which Ethernet card is down , for this you can run the "ifconfig -a" command. Using this command you can check how many internet card is present on the server and on which Ethernet card used IP address.

Let's suppose you are using eth0 on your machine, and if this Ethernet card not taking any ip address and now show on your device that means it is down right now, so please try to start Eth0 device as given below command.

[root@localhost]# ifup eth0

Device eth0 does not seem to be present, delaying initialization

If your internet card show such issue that means you have an issue with MAC address. So in this post I would explain you how to resolve such issue.

1. In this step, please check the MAC Addresses are set correctly or not. For checking this you need to go the network card directory "/etc/sysconfig/network-scripts"

[root@localhost]# cd /etc/sysconfig/network-scripts

[root@localhost]# cat ifcfg-eth0

HWADDR=”00:15:5D:00:91:91”

In the configuration file, you can see the current hardware address of eth0 card, I have show you only HWADDR entry of my eth0 file. In this directory you can see if other Ethernet card is present or not. In my Linux machine i have two Ethernet card , please find the below second Ethernet card MAC address.

[root@localhost]# cat ifcfg-eth1

HWADDR=”00:15:5D:00:91:90”

2. Now we will see which link is present on the system currently and which is not active, for this you can use the below command to check the status.

[root@localhost]# ip -o link

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN \    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000\    link/ether 00:15:5D:00:91:90 brd ff:ff:ff:ff:ff:ff

3: eth2: mtu 1500 qdisc   pfifo_fast state UP qlen 1000\ link/ether 00:15:5D:00:91:91 brd ff:ff:ff:ff:ff:ff

Here, no eth1 but there is an eth2 present on the system, so might be problem is that the eth0 is renamed to eth2 but we will confirm with below command.

[root@localhost]# dmesg | grep eth0

udev: renamed network interface eth0 to eth2

udev: renamed network interface rename3 to eth0

From this command it shows that udev rename the network interface, so in the next step we will remove the wrong entry and configure the Ethernet card 

3. Now please open the network rules file to confirm the mac address. Please open this file "/etc/udev/rules.d/70-persistent-net.rules" 

[root@localhost]# cat /etc/udev/rules.d/70-persistent-net.rules

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:90", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:91", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:91", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

Looks like there are multiple entries for the same MAC address. Removed the incorrect entry and restart the interface using below command.

[root@localhost]# ifup eth0

Now you eth0 card is up and if you are running "ifconfig -a" command you can see the eth0 card with mac address.

How to install and configure the ftp server in linux system

When you are going through this post, you can learn how to install or configured the file transfer protocol in linux operating system.

Normally, FTP server is used to upload or download the files from server machine to client machine. FTP works on TCP 20/21 protocol, TCP port 20 is used for uploading and TCP 21 port is used for downloading purpose.

Step by step method of FTP server installation and configuration:
 

➦ In the initial step , we will install the all required rpm or packages on the Linux server using "YUM" utility.[root@localhost]# yum  install  vsftpd*

If you have source rpm packages then you can install it. In our case we will install the rpm with yum. Using above command all the ftp packages and their dependency are installed.
 

➦ Once the required packages has been installed successfully on the Linux server, we will start the ftp services on the server.[root@localhost]#service  vsftpd  start

Once the service start successfully we will make permanent it so after reboot of server it would be enable always.[root@localhost]#chkconfig vsftpd on
 

➦ Now, to check the location of ftp server file which we upload or create after ftp server installation.[root@localhost]#cd /var/ftp/pub[root@localhost]#ls

And check the file which you have created after ftp server installation. If you find your created file here then you can ensure your ftp server has been installed successfully on Linux server.
 

➦ Now for checking the ftp server using login in it.

# ftp  Server IP address  ( In my case server ip is 192.168.1.240)
Name(192.168.1.240:root):anonymous
Passwd   (press enter)   --- by defult anonymous password is blank

ftp>   (It will show you have successfully enter in ftp server)
ftp> ls
pub ( will see this directory in ftp location)
ftp>cd  pub
pub> mkdir  testing
pub> permission denied  (error getting)
 

➦ To give the permission to make a directory in pub ,changes in this file[root@localhost]#vi  /etc/vsftpd/vsftpd.conf

Uncomment all these below lines
anonymous_enable=yes
anon_upload_enable=yes
anon_mkdir_write_enable=yes
save the file
 

➦ Now we will take a restart of the ftp services again. You can follow the step 2 to take a restart of ftp services.
 

➦ In this step we will provide the permission to pub folder so that client user can read/write the file and folder in the default direcoty.[root@localhost]#chmod 777  /var/ftp/pub

In my case I will give the full permission to pub folder. You can set the permission according to your project requirement.
 

➦ If you want to ensure that you are able to created and access the folder or not on ftp server then in this case you need to login again in ftp server.[root@localhost]#ftp  192.168.1.240
Name: anonymous
Passwd (enter)
ftp> Cd  pub
pub>mkdir testing
testing           (directory created)
pub>ls
testing

If you want to check the directory which we created in above text please go to the below location and find it[root@localhost]#cd  /var/ftp/pub
Pub]#ls
testing

So now you will get the file on the ftp pub folder which you created that means the permission which you provide to the user are working properly.
 

➦ You want only one user is able to login by ftp server and access only one particular folder, also not able to delete the file and folder on ftp server, having a ability of uploading and downloading through ftp server. For this thing we have to change in configuration file and chroot_list, ftpuser file.

First create a user which you want to access for ftp user[root@localhost]# useradd  -s /sbin/nologin  ttftpuser       (His shell is nologin so other user not login)[root@localhost]#passwd  ttftpuser

Now create a folder in ttftpuser which you want to give access[root@localhost]#cd  /home/ttftpuser
ttftpuser~]#mkdir  noidaftp
ttftpuser~]#chmod  777  noidaftp

Now go to the file chroot_list, add the user  only which you want to give access.[root@localhost]#vi  /etc/vsftpd/chroot_list
ttftpuser    (make a entry of user which you want to give access)

Now if you want no other user login in ftp server then entry all those user except chroot_list user in ftpuser file.[root@localhost]#vi /etc/vsftpd/ftpuser

Promartuser    (these are users on which ftp server is make )
testing

Now go to configuration file and make changes in  file and change all the parameter which is required on the configuration files.[root@localhost]#vi /etc/vsftpd/vsftpd.conf

anonymous_enable=NO
local_enable=YES
write_enable=YES
local_umask=022
dirmessage_enable=YES
xferlog_enable=YES
connect_from_port_20=YES
syslog_enable=NO
dual_log_enable=YES
vsftpd_log_file=/var/log/vsftpd.log
xferlog_file=/var/log/xferlog
xferlog_std_format=YES
ftpd_banner=*************************Welcome to blah FTP service******************
chroot_list_enable=YES
chroot_list_file=/etc/vsftpd/chroot_list
listen=YES
pam_service_name=vsftpd
userlist_enable=YES
tcp_wrappers=YES
listen_port=54321
cmds_allowed=ABOR,ACCT,ALLO,APPE,CDUP,CWD,EPRT,EPSV,FEAT,HELP,LIST,MDTM,MKD,MODE,NLST,NOOP,OPTS,PASS,PASV,PORT,PWD,QUIT,REIN,REST,RETR,RMD,RNFR,RNTO,SITE,SIZE,SMNT,STAT,STOR,STOU,STRU,SYST,TYPE,USER,XCUP,XCWD,XMKD

Save the file for above changes which is in bold text in file and restart the ftp services which is describe in step 2.[root@localhost]#service vsftpd restart

Now check login on console mode[root@localhost]#ftp  192.168.1.243 54321

Enter username:ttftpuser
Passwd..enter the passwd
ftp> you have successfully enter
ftp>ls
noidaftp      (folder you have seen)
ftp>put  vsftpd.conf        (it will upload file )
ftp>get  vsftpd.org          (it will download file)

If you want to change the user shell please run the below command method as describe below.[root@localhost]#usermod  -s  /sbin/nologin  username[root@localhost]#usermod  -s /bin/bash  username

So using above method we can easily installed and configured the ftp server on Linux operating system.