How to add linux host in Active Directory (AD) domain

Before performed such work, please collect the below information:-

Host: Server name which need to be add in AD
DA account: .da account which used to add server to domain
Domain name

Please find the below process step by step to add a server in to AD:-

[root@localhost ~]# hostname localhost.redhat.com

[root@localhost ~]# adinfo

Not joined to any domain
Licensed Features: Enabled

[root@localhost ~]#  adjoin -u xyz.da --name localhost -a localhost.redhat.com -w redhat.com

xyz.da@REDHAT.COM's password:
Using domain controller: redhat01.redhat.com writable=true
Join to domain:redhat.com, zone:Auto Zone successful
Centrify DirectControl started.
Loading domains and trusts information
........................

Note: .da account required to add server in domain

How to install or upgrade VMware Tools on linux server

You need to login on the server where you need to install or upgrade the vmware tool.

Check the status of vmtools from vcenter GUI & Servers.

/etc/vmware-tools/services.sh status

Please follow the below steps to install or upgrade the VMware Tools:-

1.    From vsphere select the virtual machine on which vmtools need to be installed and then Choose VM > Install VMware Tools.

2. As root mount the VMware Tools virtual CD-ROM image to /mnt

mount /dev/cdrom /mnt

3. go to /tmp and untar the installation file.

cd /tmp
tar zxf /mnt/VMwareTools-x.0.0-<xxxx>.tar.gz

4. Run the VMware Tools installer:

cd /tmp/vmware-tools-distrib

./vmware-install.pl -d
 

Unmount of the VMware Tools virtual CD-ROM image is done automatically.

Login to server as root and run below command to start the services:

/etc/vmware-tools/services.sh start


Run below command to check the status of vmtools:

/etc/vmware-tools/services.sh status

Uninstall the vmtools by running below command:

/usr/bin/vmware-uninstall-tools.pl

How to Set a Solaris 11 Machine's NIS Domain Name

If domainname command not showing any output then you need to check either defaultdomain or NIS domain is configured or not.

Steps which we need to follow to set the NIS domain name as describe below.

1. Please run  "cat /etc/defaultdomain" command and check the output that domain is set or not.

    #domainname

The above command shows you the current domain name on the server, if no output is display you need to set the domain by below command.

   #domainname UNIX

Run the below command to check the output again.

   #domainname

   UNIX

You can see the output. All the above command is used for checking and setting the domain name on the Solaris operating server.

2. If you want to set the domain using NIS, then first please check the NIS/DOMAIN service is running or not

root@sun:~# svcs status nis/domain

STATE          STIME    FMRI

disabled       18:20:04 svc:/network/nis/domain:default

In my Solaris machine, currently NIS domain services is stop, we will start it later once we will configured the NIS domain name on the Solaris server.

3. Now you need to configure the NIS domain for your machine ( in my case - UNIX is my domain name)

root@sun:~# svccfg -s svc:/network/nis/domain setprop config/domainname = UNIX

If you see the above command, "svccfg" command is used to configure the domain and set the proper properties.

4. In the final step once the configuration has been completed you need to refresh & enable the NIS domain service again.

root@sun:~# svccfg -s nis/domain:default refresh

root@sun:~# svcadm enable nis/domain

You can check the NIS domain service status as describe in step 2. 

5. Now you can verify the domain name using below command so we can ensure that the NIS domain name has been set successfully. 

root@sun:~# domainname

UNIX

The above command output show "UNIX" domain name which we set during the configuration, so using these above method we can easily set the NIS domain name on the Solaris operating server.

How to start/stop and enable/disable Firewall on Redhat 7 Linux system

In RHEL7, to stop/start and enable/disable the firewall is quite different from RHEL6. In Red hat 7 "firewalld" named service we used for local firewall. Please find the below example step by step to check the firewall status.

How to check status of RHEL7 firewall:

[root@localhost ~]# systemctl status firewalld
firewalld.service - firewalld - dynamic firewall daemon

Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)

Active: active (running) since Thu 2018-02-05 12:37:47 IST; 0 months 1 days ago

Main PID: 332 (firewalld)

CGroup: /system.slice/firewalld.service
           └─332 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

Feb 05 12:37:47 localhost systemd[1]: Starting firewalld - dynamic firewall daemon...
Feb 05 12:37:49 localhost systemd[1]: Started firewalld - dynamic firewall daemon.

In the above status firewall is by default enable on the linux system. It is enable automatically when system restart or on.

How to Stop and Start RHEL7 firewall:

 

Please use the below commands to start stop the firewall on redhat linux 7 operating system. 

[root@localhost ~]# service firewalld stop
Redirecting to /bin/systemctl stop  firewalld.service
Stopped firewall will start again after system's reboot.

[root@localhost ~]# service firewalld start
Redirecting to /bin/systemctl start  firewalld.service

How to Disable and Enable RHEL7 firewall:

If you want to disable permanently firewall so that after reboot it is not enable again, please use the below command.

[root@localhost ~]# systemctl disable firewalld
rm '/etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service'
rm '/etc/systemd/system/basic.target.wants/firewalld.service'

If you want to enable the firewall again run please use the below command.

[root@localhost ~]# systemctl enable firewalld
ln -s '/usr/lib/systemd/system/firewalld.service' '/etc/systemd/system/basic.target.wants/firewalld.se

How to Flush Memory Cache and Buffer Cache on Linux Server

When you run the "free -m" command and get the below output, then you observe free memory section will be low value but comparatively buffers+cache value would be higher.

Now this is not a bad thing actually since your OS has reserved this memory to speed up your most used process by keeping them in the cache. But in case any new process is executed and your system is low on memory then these cache would be automatically released to make space for memory reservation of new processes.

[root@localhost]# free -m
             total       used       free     shared    buffers     cached
Mem:          2345       1234        1145          0         24        400
-/+ buffers/cache:        664        345
Swap:         4032          0       4032

if you want to clear or free cache/buffer memory then you need to run the below command.

[root@localhost]# echo 3 > /proc/sys/vm/drop_caches

These are the different values which you can use with the above command

echo 1 is clearing only page cache

[root@localhost]# echo 1 > /proc/sys/vm/drop_caches

echo 2 is to clear free dentries and inodes

[root@localhost]# echo 2 > /proc/sys/vm/drop_caches

echo 3 is clearing page cache, dentries and inodes

[root@localhost]# echo 3 > /proc/sys/vm/drop_caches

SSH login without password in linux

If you want to connect one Linux host to other Linux host through SSH with password-less connection then you need to perform below steps.

Lets suppose you need password-less login from host "server01" / user "redhat" to host "server02" / user "centos".

1. First login in on "server01"as user "redhat" and generate a pair of authentication keys.

[redhat@server01]# ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/redhat/.ssh/id_rsa):
Created directory '/home/redhat/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/redhat/.ssh/id_rsa.
Your public key has been saved in /home/redhat/.ssh/id_rsa.pub.
The key fingerprint is:
1e:4f:05:79:3a:9f:96:7c:2b:ad:e9:58:37:sc:37:e4 redhat@server01

Note: Do not enter a passphrase.

2. Now you use ssh to create a directory ~/.ssh as user "centos" on server02.

Note: If directory already exist, you do not create it again.

[redhat@server01]# ssh centos@server02 mkdir -p .ssh

centos@server02's password:

Finally append redhat's new public key to centos@server02:.ssh/authorized_keys and enter centos's password one last time:

3. Now copy the rsa key to server 02 ssh authorized_keys file

[redhat@server01]# cat .ssh/id_rsa.pub | ssh centos@server02 'cat >> .ssh/authorized_keys'

centos@server02's password:

Now you can log into server02 as "centos" from server01 as "redhat"a without password.

4. Now you can test the password less connection.

[redhat@server01]# ssh centos@server02

You are successfully login on the server02 without any password.

Note:  In case of any permission issue you need to set "700" permission on .ssh folder on server02.

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