LINUX AND VMWARE STUFF

This Blog is to share our knowledge and expertise on Linux System Administration and VMware Administration

Thursday, April 19, 2018

Facter command in Linux

Thursday, April 19, 2018 0
Facter command is used to Collect and display facts about the current server. The library behind Facter is easy to expand, making Facter an easy way to collect information about a system information such as hardware details, network settings, virtualization type and kernel/OS information from within the shell or within Ruby. If no facts are specifically asked for, then all facts will be displayed.

If we want to use facter command, we need to install facter rpm.

Display all facts

[root@testserver manifests]# facter
architecture => x86_64
augeasversion => 1.1.0
bios_release_date => 01/06/2018
bios_vendor => Xen
bios_version => 4.4.4OVM
blockdevice_xvda_size => 53687091200
blockdevices => xvda
domain => puppet.test.com
facterversion => 2.4.4
filesystems => ext4,iso9660
fqdn => testserver.puppet.test.com
gid => root
hardwareisa => x86_64
....
....
uptime_days => 62
uptime_hours => 1491
uptime_seconds => 5368909
uuid => 0004FB00-0006-0000-7071-48CB71E70F8A
virtual => xenhvm

Display a single fact

[root@testserver ~]#  facter interfaces
eth0,eth1,eth2,lo

Facts format as JSON

[root@testserver ~]# facter --json architecture kernel  uptime timezone puppetversion bios_vendor
{
  "timezone": "CAT",
  "uptime": "62 days",
  "architecture": "x86_64",
  "kernel": "Linux",
  "bios_vendor": "Xen",
  "puppetversion": "3.8.1"

Facts format as YAML

[root@testserver  ~]# facter --yaml architecture kernel  uptime timezone puppetversion bios_vendor
---
bios_vendor: Xen
kernel: Linux
uptime: 62 days
timezone: CAT
architecture: x86_64
puppetversion: 3.8.1

Facter will produce output by below format.
a. JSON
b. YAML
c. Plaintext
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Thursday, April 12, 2018

How to change the default login shell by command line in linux server?

Thursday, April 12, 2018 0
By using chsh command we can change the default login shell to other shell.

 By using -l option we can list the available login shell on linux server.

 [root@testserver ~]# chsh -l
/bin/sh
/bin/bash
/sbin/nologin
/bin/dash
/bin/tcsh
/bin/csh
/bin/ksh

 Then which user login shell need to change, we can change by below command. (If a shell is not given on the command line, chsh prompts for one)

 [root@testserver ~]# chsh hygmtng7
Changing shell for hygmtng7.
New shell [/bin/ksh]: /bin/bash
Shell changed.

 Before
[root@testserver ~]# cat /etc/passwd | grep -i hygmtng7
hygmtng7:x:20009:20009::/gmtng7/hyperion:/bin/ksh

 After
[root@testserver ~]# cat /etc/passwd | grep -i hygmtng7
hygmtng7:x:20009:20009::/gmtng7/hyperion:/bin/bash
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Thursday, April 5, 2018

How to use --exclude option in du command

Thursday, April 05, 2018 0
du command is used to estimate file space usage.

 Sometime we need to exclude some folder or files while running du command.
For that we can use below option to achieve that.

 [root@testserver /]# du -sh * --exclude=repository --exclude=oem1

 The above command will exclude the repository & oem folder  under / path.

 Hope it helps.
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Sunday, March 18, 2018

How to Add SSH Public Key to Remote Server(s) in a Single Command.

Sunday, March 18, 2018 0
Below command is used to copy the key to single server.

# cat id_rsa.pub | ssh username@servername 'cat >> /home/user/.ssh/authorized_keys'

Below command is used to copy the key to multiple server. We can use for loop.

# for i in  `cat serverlist`; do echo $i; cat id_rsa.pub | ssh username@servername 'cat >> /home/user/.ssh/authorized_keys'; done

Hope it helps.
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Wednesday, February 28, 2018

How to kill the IDLE pts/tty session in Linux Server?

Wednesday, February 28, 2018 0
 Kill the IDLE pts/tty session in Linux Server

Situation:
    Sometime script command may not be completed properly or sometime improperly closed ssh session makes the idle pts/tty session.
           
[root@dbserver ~]# w
 14:18:28 up 31 days,  4:18,  4 users,  load average: 3.35, 3.42, 3.41
USER     TTY      FROM  LOGIN@   IDLE     JCPU   PCPU  WHAT
root        pts/2    -            27Jan18   31days  0.00s  0.00s   script -a /os_backup_fs/patches/DB_Server/logs/dbserver_Postwork-1.log

 Solution:
Here, sometime ps -ft command will not respond

[root@dbserver ~]# ps -ft pts/2
UID         PID   PPID  C STIME TTY          TIME CMD

So, search with process and kill the process id.

[root@dbserver ~]# ps -ef | grep -i /os_backup_fs/patches/DB_Server/logs/dbserver_Postwork-1.log
root     202948 185999  0 14:18 pts/4    00:00:00 grep -i /os_backup_fs/patches/DB_Server/logs/dbserver_Postwork-1.log
root     271243 113886  0 Jan27 pts/1    00:00:00 script -a /os_backup_fs/patches/DB_Server/logs/dbserver_Postwork-1.log
root     271245 271243  0 Jan27 pts/1    00:00:00 script -a /os_backup_fs/patches/DB_Server/logs/dbserver_Postwork-1.log
[root@dbserver ~]# kill -9 271243

Hope it helps.
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Monday, February 26, 2018

How to create VLAN interface by using comand line in RHEL7

Monday, February 26, 2018 0
By using nmcli command we can craete the VLAN interface in RHEL7.

VLANs are isolated broadcast domains that run over a single physical network. They allow you to segment a local network and also to "stretch" a LAN over multiple physical locations. Most enterprises implement this on their network switching environment, but in some cases, the tagged VLANs reach your server.

For this case, our physical network interface is called enp0s3. The VLAN's ID is 501, and the IPv4 address is 192.168.1.10, with a subnet mask of 255.255.255.0 and a default gateway of 192.168.1.1.

Create vlan
[root@nsk ~]# nmcli connection add type vlan dev enp0s3 id 501 ip4 192.168.1.10/24 gw4 192.168.1.1
Connection 'vlan' (a01bd6a3-a486-4c5b-83af-73d7344cc388) successfully added.

Activate the connection
[root@nsk ~]# nmcli connection up vlan
Connection successfully activated (D-Bus active path: /org/freedesktop/NetworkManager/ActiveConnection/3)

Check the Connection
[root@nsk ~]# nmcli connection show
NAME     UUID                                                                 TYPE                   DEVICE
enp0s3  191fbaab-7ac3-4616-9368-3b006cba3574      802-3-ethernet     enp0s3
vlan        a01bd6a3-a486-4c5b-83af-73d7344cc388      vlan                      enp0s3.501

[root@nsk ~]# nmcli device status
DEVICE          TYPE           STATE         CONNECTION
enp0s3          ethernet       connected    enp0s3
enp0s3.501   vlan              connected    vlan
lo                  loopback       unmanaged   --

[root@nsk ~]# nmcli device show enp0s3.501
GENERAL.DEVICE                   :    enp0s3.501
GENERAL.TYPE                      :      vlan
GENERAL.HWADDR                :     08:00:27:93:16:4B
GENERAL.MTU                        :    1500
GENERAL.STATE                    :    100 (connected)
GENERAL.CONNECTION        :   vlan
GENERAL.CON-PATH             :    /org/freedesktop/NetworkManager/ActiveConnection/3
IP4.ADDRESS[1]                     :      192.168.1.10/24
IP4.GATEWAY                         :      192.168.1.1
IP6.ADDRESS[1]                     :       fe80::ecb7:3969:728f:a67b/64
IP6.GATEWAY                         :       --
[root@nsk ~]#

The command line to create a VLAN with nmcli is very basic as it uses default values.

Below command will full option to create detailed VLAN interface.
[root@nsk ~]# nmcli con add help
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Saturday, February 17, 2018

How to change the Linux user's password in single command

Saturday, February 17, 2018 0
Changing the Linux user's password in one command

 Chpasswd reads a list of user name and password pairs from standard input and uses this information to update a group of existing users

 chpasswd - update passwords in batch mode

 Syntax    -  user_name:password

  By default the supplied password must be in clear-text. Also the password age will be updated, if present.

 #echo user:password | /usr/sbin/chpasswd
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Friday, February 16, 2018

Default Physical extent size in RHEL5, RHEL6 and RHEL7

Friday, February 16, 2018 0
Default Physical extent size in RHEL5, RHEL6 and RHEL7

Each physical volume is divided chunks of data, known as physical extents, these extents have the same size as the logical extents for the volume group.

Making the PE too small wouldn't be recommended, as the maximum volume size is 65,536 PEs, so if you reduce this to 1MB, you end up with volumes not larger than 64GB.

RHEL 5 - 32 M
RHEL 6 - 4 MB  (maximum we can create 256 GB file system)
RHEL 7 - 4 MB
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