Debug School: Manish Mishra

Git Commands

Manish Mishra — Fri, 18 Nov 2022 07:29:00 +0000

Basic commands:

to check installed version
git --version
to set user name and email for current repo
git config user.name "Manish Mishra"

git config user.email "manishsmishra97@gmail.com"

to list the current configurations for a repo
git config --list
first time to initialize a project (Run inside project Directory)
git init
check status
git status
Git Add - > adds selected changes to staging area
git add file1 file2
Commit without -m it will pop out editor for text message
git commit
git commit -m "Your Message"
add all changes to stage at once
git add .
add and commit simultaneously
git commit -a -m "message"
to view details about a particular commit
git show
to view commit history
git log
or
git log --oneline
rename file
git mv
remove file that is tracked
git rm
remove a file that is not staged or committed (Untracked)
git clean -fd
clone a repo
git clone
pull a repro (pull = fetch + merge)
git pull
add repo link to the local repo
git remote add origin
After adding above , to push to a remote repo
git push origin

Undoing changes:

it will undo all the changes which are done to the file that are unstaged/uncommited
it will revert the changes and reflect the changes per current HEAD
git restore
remove file from stage area
git restore --staged
revert creates a new commit to undo the changes as per the commit hash provided

git revert

Git Diff:

-compares staging area and working directory

only show unsatged changes
git diff
git diff
get difference between two commits
git diff
will list changes between tips of the two branch
git diff

Branching:

view existing branches in current repo
git branch
should not include spaces
just makes the branch
does not switch to the branch (Head does not change)
git branch

-checkout the branch
git checkout -b
or
git checkout

to list remote tracking branch git branch -r

Merge

switch to the main branch, and use below git merge e.g: if you want feature branch to be merged in main git checkout main git merge feature

based on the commit histories; after creation of the feature branch from main: there are multiple cases of merge:
Fast-Forward: simplest type
In this the feature branch have single of multiple commit since creating the branch while the master branch does not have any commit in that period.

cherry-pick:
merge particular feature from feature branch to be merged into master

git cherry-pick

Tags:

creates a tag and attached it to the current commit
git tag
to tag a particular commit
git tag
delete tag

git tag -d

push all tags

git push --tags

single tag

git push origin

get details of tag

git show

Docker tmpfs mount

Manish Mishra — Wed, 16 Nov 2022 05:12:00 +0000

It is one of the 3 options available for user to store data. unlike volume & mountfs, the data stored under tmpfs mount is not persistent, it is stored in the host memory.
This is used when we don't want to write sensitive data or data that relates to non-persistent application state in the container layer or on the host FS.
usage:

1st Method:

docker run -itd --name temp_alpine --tmpfs /u01/temp alpine

2nd Method:

docker run -itd --name temp_alpine --mount
type=tmpfs,destination=/u01/temp alpine

Docker image

Manish Mishra — Tue, 15 Nov 2022 06:43:00 +0000

Docker Image is a collection of multiple Filesystems.
Each docker Image consist of 1 Root FS + 1 User FS which forms the Base Image and it can have multiple number of application specific FS.
Each of this Filesystem corresponds to a layer, and each layer are identified by a unique Layer ID.
Each of the Layers have a corresponding Parent layer except the root layer.
When a container is created, all of the layers defined in the images are merged into a single Mount which is then attached to the runtime user.
Once the container is running , any file related changes made into the container gets recorded in two location diff and merged.
diff directory is persistent, while the merged directory is removed when the container is stopped/killed.
If the stopped container is started back again a new merged is created from the layers defined in image and the changes from the diff directory is applied to that merged and is then mounted to the runtime user.
Docker Root Dir can be located by using docker info command.
Docker uses Sha2-256 algorithm to hash and manage the FS.
Depending on the Storage driver, the FS are created in the corresponding storage driver's name folder e.g. overlay2 under docker root directory.
The Meta data related to the container is stored under Image directory.

Docker Commands 2

Manish Mishra — Tue, 15 Nov 2022 04:51:00 +0000

Docker Update:

It Dynamically updates container configuration. With the use of this command we can set a limit on the resource that a container can consume. Resources such as memory size, no. of cpu, cpu shares, swap memory size, pid limit and more. Most of the this limits can be set on a running container.

Docker Wait:
The ‘docker wait’ is a command that is used to wait or block until one or more containers stop, and then it outputs their exit codes.

Docker Commands

Manish Mishra — Mon, 14 Nov 2022 10:06:59 +0000

Docker pause:

Docker pause suspends all the process in the container by sending SIGSTOP signal, but the contents of the memory remains intact and will be available yo use when the container is unpaused

Docker unpause:

Docker unpause will subsequently resumse all the suspended process by docker pause.
Docker

Docker stop:

The Docker stop command will first send a SIGTERM Signal which allows the main process a grace period to clean up the processing, after some time a SIGKILL signal is sent to stop the main process. We can specify the time duration before the docker send the SIGKILL

use: --time 10s , this will allow application 10 sec to gracefully termiate , before sending the KIll signal.

When a process is gracefully ended by SIGTERM, the exit code for the operation is 0

Docker kill:

When Docker kill command is fired a SIGKILL signal is sent to the main process of the container. The SIGKILL signal kills the process in the container immediately thereby stopping all the running processing.
When a process is kill via SIGKILL the exit code for the operation is 137

Docker Summary

Manish Mishra — Mon, 14 Nov 2022 07:27:01 +0000

What is Docker?

Docker is an container orchestration/management Tools.
With Docker we can perform various management operations on containers such as create, start, stop, kill, restart. Why Docker?
Buy creating containers using docker we can
- save cost - hardware requirement is minimal.
- save time - from provisioning to booting to management, the time taken is far less than that taken by VM's or physical machines.
- improve work quality - with the effective utilization of the resources and easy management of containers. What is Container?
Containers allow us to isolate kernel process and help us to run applications using images.

Docker workflow

Docker run - docker client - docker daemon - registry docker hub - image is pulled - container is created.

How container created?

Docker image parts - BOOT FS , ROOT FS , USERS , Applications
Using the Docker base image, docker initializes namespaces and runs the application