Docker image push

To push a image to docker hub follow below,

Use docker container ls command to list running container image details.

 [root@jkcli ~]# docker container ls
CONTAINER ID   IMAGE     COMMAND              CREATED          STATUS          PORTS                                   NAMES
cb72f5d90279   httpd     "httpd-foreground"   21 minutes ago   Up 21 minutes   0.0.0.0:8080->80/tcp, :::8080->80/tcp   jkapache
[root@jkcli ~]#

Use docker container commit command to commit container as a image with tag.

[root@jkcli ~]# docker container commit cb72f5d90279 jk-httpd:test
sha256:8daf5db17d6fdb0fd6ceea7e4d6ed38d22c3fdad6375f479ed6fc7986eec4a61
[root@jkcli ~]#

You can now list and see the created image is available.

[root@jkcli ~]# docker image ls
REPOSITORY   TAG       IMAGE ID       CREATED              SIZE
jk-httpd     test      8daf5db17d6f   About a minute ago   189MB
httpd        latest    30287d899656   7 days ago           138MB
nginx        latest    d1a364dc548d   5 weeks ago          133MB
[root@jkcli ~]#

To upload your newly created image to docker hub. First you have to login to docker with docker login credentials. To do this use, docker login command.

[root@jkcli ~]# docker login

Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one.

Username: karthick04

Password: XXXXX

Now we can tag the image across the repository created in the docker hub. Here I have already created a repository karthick04/jkrepo. 

Command : docker tag source_image:tag target_image:tag

[root@jkcli ~]# docker tag jk-httpd:test karthick04/jkrepo:version1
REPOSITORY          TAG        IMAGE ID       CREATED         SIZE
karthick04/jkrepo   version1   8daf5db17d6f   9 minutes ago   189MB
jk-httpd            test       8daf5db17d6f   9 minutes ago   189MB
httpd               latest     30287d899656   7 days ago      138MB
nginx               latest     d1a364dc548d   5 weeks ago     133MB
[root@jkcli ~]# 

[root@jkcli ~]# docker image ls

To push the image finally to the docker hub use docker image push command. 

[root@jkcli ~]# docker image push karthick04/jkrepo:version1
The push refers to repository [docker.io/karthick04/jkrepo]
c54811c7708d: Pushed
dfd488a286c9: Pushed
15176fdb9a61: Pushed
61172cb5065c: Pushed
9fbbeddcc4e4: Pushed
764055ebc9a7: Pushed
version1: digest: sha256:c6271d65a6b6a4b6274adcbd51b0ddd5dab1b94b8112ccdbd7d407770bdb238b size: 1578
[root@jkcli ~]#

Successfully we have pushed the image to docker hub, we can see this image in docker hub now

https://hub.docker.com/r/karthick04/jkrepo

Also you can pull same image using docker pull karthick04/jkrepo:version1

[root@jkcli ~]# docker pull karthick04/jkrepo:version1
version1: Pulling from karthick04/jkrepo
b4d181a07f80: Already exists
4b72f5187e6e: Already exists
12b2c44d04b2: Already exists
ef481fc2a03a: Already exists
d483d945fcab: Already exists
6b6a1b4ae105: Pull complete
Digest: sha256:c6271d65a6b6a4b6274adcbd51b0ddd5dab1b94b8112ccdbd7d407770bdb238b
Status: Downloaded newer image for karthick04/jkrepo:version1
docker.io/karthick04/jkrepo:version1
[root@jkcli ~]# docker image ls
REPOSITORY          TAG        IMAGE ID       CREATED          SIZE
karthick04/jkrepo   version1   8daf5db17d6f   26 minutes ago   189MB
httpd               latest     30287d899656   7 days ago       138MB
nginx               latest     d1a364dc548d   5 weeks ago      133MB
[root@jkcli ~]#

Bash into a container

Bash into a container

After creating a container in detach mode. If you are looking to bash into a container then you can follow this.

There is a docker exec command that can be used to execute a command on a container that is already running.

Use docker ps to get the name of the existing container

[root@jkcli ~]# docker ps

CONTAINER ID   IMAGE     COMMAND              CREATED          STATUS          PORTS                                   NAMES

cb72f5d90279   httpd     "httpd-foreground"   17 minutes ago   Up 17 minutes   0.0.0.0:8080->80/tcp, :::8080->80/tcp   jkapache

[root@jkcli ~]#

Use command docker exec -it <container name> /bin/bash to bash into a container

[root@jkcli ~]# docker exec -it cb72f5d90279 /bin/bash

root@cb72f5d90279:/usr/local/apache2#

Beginner common mistakes with Docker container

Container run/re-run

When you create a container and then exit it. The container only stops but it still is lying there in stopped/Exited state. You cannot re-run a new container with the same name.

Running httpd container

[root@jkcli ~]# docker container run --name jkapache -p 8080:80 httpd
Unable to find image 'httpd:latest' locally
latest: Pulling from library/httpd
b4d181a07f80: Pull complete
4b72f5187e6e: Pull complete
12b2c44d04b2: Pull complete
ef481fc2a03a: Pull complete
d483d945fcab: Pull complete

Later when i exit this container and try to run same container it will give me below error. 

[root@jkcli ~]# docker container run --name jkapache -p 8080:80 httpd -d

docker: Error response from daemon: Conflict. The container name "/jkapache" is already in use by container "28c5bc35be99e59baf5ce076bdfad683188b64d2e47d7483e8cfc86a764f832c". You have to remove (or rename) that container to be able to reuse that name.

see 'docker run --help'.

However if you check "docker container ls" command, it will show no container running. 

[root@jkcli ~]# docker container ls

CONTAINER ID   IMAGE     COMMAND   CREATED   STATUS    PORTS     NAMES

[root@jkcli ~]# 

This is because docker container ls command will show only running containers at that point in time. 

we have to use -a to list all containers.

[root@jkcli ~]# docker container ls -a

CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS                          PORTS     NAMES

28c5bc35be99   httpd     "httpd-foreground"       2 minutes ago   Exited (0) About a minute ago             jkapache

1cb4b275776a   nginx     "/docker-entrypoint.…"   10 days ago     Exited (0) 10 days ago                    jk

[root@jkcli ~]#

Remove docker container

Now remove these docker container and then we can try running the docker like below,

[root@jkcli ~]# docker container ls -a

CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS                      PORTS     NAMES

28c5bc35be99   httpd     "httpd-foreground"       15 minutes ago   Exited (0) 14 minutes ago             jkapache

1cb4b275776a   nginx     "/docker-entrypoint.…"   10 days ago      Exited (0) 10 days ago                jk

[root@jkcli ~]# docker container rm 28c5bc35be99

28c5bc35be99

Running docker container with detatch

[root@jkcli ~]# docker container run -d --name jkapache -p 8080:80 httpd

cb72f5d90279fcdef02b3715a04cec20043c23f10a8e548ac7a0cf4789640788

[root@jkcli ~]# docker container ls

CONTAINER ID   IMAGE     COMMAND              CREATED         STATUS         PORTS                                   NAMES

cb72f5d90279   httpd     "httpd-foreground"   4 minutes ago   Up 4 minutes   0.0.0.0:8080->80/tcp, :::8080->80/tcp   jkapache

[root@jkcli ~]#

Docker installation issues

Docker Installation issues

 
This document is intended to cover Docker Engine installation issue. 

Scenario 1: Installing Docker CE on CentOS 8.4 Server GUI

Installing Docker CE on Centos 8.4 should be pretty simple using the script https://get.docker.com/

However you should consider some pre-requisites to perform a smooth installation of Docker CE 

Version Involved:

Linux : CentOS Linux release 8.4.2105

Docker : Docker version 20.10.7, build f0df350

CentOS 8.4 Server GUI version is found to have default containerd packages which would conflict Docker CE installation. Before proceeding with Installation we must remove these conflicts.

 

Packages to be removed : runc, container-selinux

#yum remove runc
#yum remove container-selinux

Now we can install Docker CE successfully using Docker installation script

curl -fsSL https://get.docker.com -o get-docker.sh

sh get-docker.sh

Run levels in Linux

This document is intended to brief us about the Linux booting procedure. 

Once the kernel finished its loading, /etc/initab file is loaded.
The /etc/inittab file is used to set the default run level for the system. Applications/services that are started by init are located in the /etc/rc.d folder. Within this directory there is a separate folder for each run level, eg rc0.d, rc1.d, and so on.

There are 7 Runlevel in linux 0 to 6 explained below,

0 - /etc/rc.d/rc0.d - This is system HALT - this run level will shutdown the system.

1 - /etc/rc.d/rc1.d - This is single user mode - booting with this runlevel will boot with basic command line interface without loading network modules/graphics. Doesn't allow non-root login.

2 - /etc/rc.d/rc2.d - This is multi-user mode - When booting with runlevel 2, network module is not loaded.

3 - /etc/rc.d/rc3.d - This is multi-user mode with network - Boots with network modules and allows multi user modules. System will be booting normally.

4 - /etc/rc.d/rc4.d - This is still undefined/not usable can be user defined.

5 - /etc/rc.d/rc5.d- This is similar to the init level 3 which boots with X11 graphic interface.

6 - /etc/rc.d/rc6.d - This is reboot - When runlevel 6 is called it will reboot the system.

Init is the program that bring up all the other processes. It runs as a daemon and Process ID for Init is 1. This is the first process to run on a linux/unix machine. 

You can provide which Runlevel the system will boot with as a kernel boot parameter.

Network Gateway

Network Gateway

In computer network, a network gateway is a device/software which acts as a gate between intranet/internet. Any piece of information that is on the internet and you want to access them without passing through the Network gateway you will not be able to access them.

Like the name gateway -  It is like a gate in your room where without opening your gate you cannot access/reach outside world.

A network gateway can be a router/L3 Switch/Proxy Software/Firewall.

When you assign gateway IP to a desktop/server you must confirm that from your desktop/server you are able to reach the gateway using ping.

Root user password reset in Ubuntu

You can reset your root / user password if not able to login to your Desktop. Follow below steps and you will be able to login easily.

Step 1 : While booting press and hold shift key.  You will get a screen as below.

Step 2: Select Linux recovery mode and hit enter, you will get a screen as below. 

Step 3: Scroll and select root drop to root shell prompt option then you will  see a shell screen in the bottom.

Step 4: You have to mount your drives so now type in the shell as

mount –o rw,remount /

step 5 : Now if you want to know the users in this computer type

ls /home

step 6 : It will show the list of users in computer. now for example if you want to reset the passwd of  susan user, then type as

passwd susan (i.e, passwd username)

step 7 : Now it will ask for a new unix password, enter the required passwd.

Step 8: Again retype the passwd.

Step 9 : Now you have successfully changed your password. So type exit. It will take you to the screen as below.

Step 10 : Select resume so that your computer reboots.

Note: Some computer does not go back to GUI mode, don’t worry just restart your system once. It will be fine.

 PASSWORD RESET DONE!!!