LINUX AND VMWARE STUFF

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

Thursday, January 11, 2018

Display the timestamping capabilities of particular interface of Linux Server.

Thursday, January 11, 2018 0
Many NICs support software timestamping, but to query your own interface, use the below command, which will display the timestamping capabilities of particular interface

 NAME
       ethtool - query or control network driver and hardware settings

 [root@nsk ~]# ethtool -T enp0s3
Time stamping parameters for enp0s3:
Capabilities:
        software-transmit     (SOF_TIMESTAMPING_TX_SOFTWARE)
        software-receive      (SOF_TIMESTAMPING_RX_SOFTWARE)
        software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
PTP Hardware Clock: none
Hardware Transmit Timestamp Modes: none
Hardware Receive Filter Modes: none
[root@nsk ~]#
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Monday, January 8, 2018

Working with Docker Container - Starting a container

Monday, January 08, 2018 0

Starting a container

Listing images

 We can list the images available on the system running the Docker daemon. These images might have been pulled from the registry, imported through the docker command, or created through Docker files.
root@Docker:~# docker images
REPOSITORY                     TAG                 IMAGE ID               CREATED            SIZE
nskselvan/nsk                      latest              b2f0c17eed23        2 months ago        197MB
centos-latest                        latest              2083898799b1       2 months ago        197MB
wordpress                            latest              224b7eef6944        3 months ago        408MB
mysql                                   5.7                  b4e78b89bcf3        3 months ago        412MB
registry                                 2                    28525f9a6e46         3 months ago        33.2MB
localhost:5000/reg               latest              28525f9a6e46         3 months ago        33.2MB
centos                                  latest             196e0ce0c9fb          3 months ago        197MB
localhost:5000/centos-ka     latest             196e0ce0c9fb          3 months ago        197MB

For help with the docker images use --help

 Once we have images, we can use them to start the containers. In this recipe, we will start a container with the fedora:latest image and see what all things happen behind the scene.
syntax  : docker run [ OPTIONS ]  IMAGE[:TAG]  [COMMAND]  [ARG...]

 root@Docker:~# docker run -i -t --name=centos centos /bin/bash
[root@6d65e303381c /]# uptime
 04:07:13 up  1:02,  0 users,  load average: 0.02, 0.01, 0.00

 Here,
The -i option starts the container in the interactive mode
The -t option allocates a pseudo-tty and attaches it to the standard input

 So, with the preceding command, we start a container from the centos:latest image, attach pseudo-tty, name it centos, and run the /bin/bash command. If the name is not specified, then a random string will be assigned as the name.
Also, if the image is not available locally, then it will get downloaded from the registry first and then run. Docker will run the search and pull commands before running the run command.

 Under the hood, Docker:

 Will merge all the layers that make that image using UnionFS.
Allocates a unique ID to a container, which is referred to as Container ID.
Allocates a filesystem and mounts a read/write layer for the container. Any changes on this layer will be temporary and will be discarded if they are not committed.
Allocates a network/bridge interface.
Assigns an IP address to the container.
Executes the process specified by the user.
Also, with the default Docker configuration, it creates a directory with the container's ID inside /var/lib/docker/containers, which has the container's specific information such as hostname, configuration details, logs, and /etc/hosts.

 To exit from the container, press Ctrl + D or type exit. It is similar to exiting from a shell but this will stop the container.
The run command creates and starts the container. With Docker 1.3 or later, it is possible to just create the container using the create command and run it later using the start command, as shown in the following example:

 root@Docker:~# ID=$(docker create -t -i centos bash)
root@Docker:~# docker start -a -i $ID
[root@8813d555d0dc /]#

 The container can be started in the background and then we can attach to it whenever needed. We need to use the -d option to start the container in the background:
root@Docker:~# docker run -d -i -t centos /bin/bash
e3bfe67aa1759c5ccd0e8e061595b8214881673c4df599f9652a58369df7d948

 The preceding command returns the container ID of the container to which we can attach later, as follows:
root@Docker:~# docker attach e3bfe67aa1759c5ccd0e8e061595b8214881673c4df599f9652a58369df7d948
[root@e3bfe67aa175 /]#

 The --read-only option of the run command will mount the root filesystem in the read-only mode:
root@Docker:~# docker run --read-only -d -i -t centos /bin/bash
b613fbc39be2b46cbc485d76bae3f2e7f1781c570e32b6509dab5345d45b6e04

 Note: this option just makes sure that we cannot modify anything on the root filesystem, but we are writing on volumes
For help with the docker run use --help
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lsblk command in Linux

Monday, January 08, 2018 0
NAME
       lsblk - list block devices

lsblk lists information about all available or the specified block devices.  The lsblk command reads the sysfs filesystem to gather information. The command prints all block devices (except RAM disks) in a tree-like format by default

 [root@nsk postfix]# lsblk
NAME                           MAJ:MIN RM  SIZE    RO TYPE MOUNTPOINT
sda                                     8:0       0      20G     0    disk
├─sda1                              8:1       0        1G     0    part /boot
└─sda2                              8:2       0      19G     0    part
  ├─centos-root              253:0       0      17G     0    lvm  /
  └─centos-swap            253:1       0        2G     0    lvm  [SWAP]
sr0                                     11:0       1  1024M     0     rom

 The  default  output, as well as the default output from options like --fs and --topology, is subject to change.

 [root@nsk postfix]# lsblk --fs
NAME               FSTYPE           LABEL UUID                                          MOUNTPOINT
sda
├─sda1              xfs                    7b4cffc6-3fe2-4ad9-9be9-ea83e11532fc           /boot
└─sda2              LVM2_member DQjmHN-fso4-Mu4t-3l1V-Yogj-ksTH-ROFiK7
  ├─centos-root  xfs                    4d056c54-3e98-4bbd-953d-ad49d24e89a3       /
  └─centos-swap swap               e97f5f2c-66b2-42c6-9baf-544123ee9abf          [SWAP]
sr0

 [root@nsk postfix]# lsblk --topology


 For mre help, please refer man pages
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Sunday, January 7, 2018

How to modify the Default Physical extent size of Physical Volume?

Sunday, January 07, 2018 0

There are 2 situation for modifying or Setting the Default Physical extent size in LVM.

1. Create a volume group with new Physical extent size. This method will be used before creating logical volume on that Volume Group.

 #vgcreate -s PE_SIZE 

 Here,
-s  --physicalextentsize Size[m|UNIT] - Sets the physical extent size of PVs in the VG.  The value must be either a power of 2 of at least 1 sector (where the sector size is the largest sector size of the PVs currently used in the VG), or at least 128KiB.  Once this value has been set, it is difficult to change without recreating the VG,unless no extents need moving.

2. Modify the Existing value of Physical extent size.

 - remove all Logical Volumes of the Volume Group with lvremove
- do a vgreduce on that VG.
- "vgchage -an" on that VG
- vgremove that VG
- setup the VG with large PE size (vgcreate -s PE_SIZE)

 A more "Forceful" approach is:
- "vgchange -a n" on the VG
- "pvcreate -ff" on all its PVs
- setup the VG with large PE size (vgcreate -s PE_SIZE)
Tags # LVM Continue Reading
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Saturday, January 6, 2018

Display what extents are allocated on the physical volume to logical volume

Saturday, January 06, 2018 0
We can see what extents are allocated on the physical volume

 NAME
       pvdisplay - Display various attributes of physical volume(s)
   
pvdisplay shows the attributes of PVs, like size, physical extent size, space used for the VG descriptor area, etc. Here pvdisplay along with options --maps will show the what extents are allocated on the physical volume to the lv.

 [root@nsk postfix]# pvdisplay --maps /dev/sda2
  --- Physical volume ---
  PV Name                /dev/sda2
  VG Name                centos
  PV Size                  <19.00 GiB / not usable 3.00 MiB
  Allocatable              yes (but full)
  PE Size                   4.00 MiB
  Total PE                   4863
  Free PE                   0
  Allocated PE           4863
  PV UUID                 DQjmHN-fso4-Mu4t-3l1V-Yogj-ksTH-ROFiK7

   --- Physical Segments ---
  Physical extent 0 to 511:
    Logical volume      /dev/centos/swap
    Logical extents      0 to 511
  Physical extent 512 to 4862:
    Logical volume      /dev/centos/root
    Logical extents      0 to 4350

 Here,
         -m  --maps  Display the mapping of physical extents to LVs and logical extents.
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Tee command in Linux

Saturday, January 06, 2018 0
NAME
       tee - read from standard input and write to standard output and files
   
Copy standard input to each FILE, and also to standard output

 options:
-a, --append  - append to the given FILEs, do not overwrite
-i, --ignore-interrupts - ignore interrupt signals
Ex : 
    [root@nsk postfix]# cat main.cf | egrep -v "^#|^$" |tee -a main.cf_catoutput

 Here,
Tee command will read the output of cat command & write the standard output to a specified file.
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Friday, January 5, 2018

Single command to take the backup and removes the commented and blank lines in a file

Friday, January 05, 2018 0
We can achieve by using 2 ways in Linux.

SED Command:

Normally, we will take back up and tidy the most of the configuration file. There is a tendency for many software packages to over comment their configurations. This can cause issues where you think that you have implemented a change; however, it was also set later on and you may not have noticed it.
Postfix, main.cf configuration file having 679 lines. We will back up the file so that we do not lose comments and documentations, but we will also have a new working file with less than 10 percent of the number of lines. The following command shows how this is done
[root@nsk etc]# cat /etc/postfix/main.cf | wc -l
679

 [root@nsk etc]# sudo sed -i.bak '/^#/d;/^$/d' /etc/postfix/main.cf
Here:
#/d   - Remove the commented line
^$   - Remove the blank line

 [root@nsk etc]# cat postfix/main.cf | wc -l
25
Above sed command reduces the file from 679 lines to 25 lines and is far easier to work with. We can now edit this file without any distractions. We will add two new lines and edit two existing lines to the /etc/postfix/main.cf file. This will need to be edited as root.

CAT Command:

We can use below command also to achieve the above output. 

 [root@nsk etc]# [root@nsk postfix]# cat main.cf.bak | egrep -v "^#|^$" |tee -a main.cf_catoutput
[root@nsk postfix]# cat main.cf_catoutput | wc -l
25

Sed command will take the backup of existing file & the output will be saved in existing name. Here Cat command output will be saved in different name.

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