Understanding SCP, Systemctl, Logs, Volume mount and More in Simple Terms

What is SCP?

SCP stands for Secure Copy Protocol. It’s a way to transfer files between computers securely over a network. If you have files on one machine and need to move them to another, SCP is a useful tool.

Basic SCP Commands:

Copy a file from your local machine to a remote machine:
```
 scp -i [Private-Key] [Local-File] [Username]@[Remote-Server-Address]:[Remote-Destination-Path]
```
- [Private-Key] is your SSH private key for authentication.
- [Local-File] is the file you want to transfer.
- [Username] is your username on the remote server.
- [Remote-Server-Address] is the address of the remote server.
- [Remote-Destination-Path] is where you want to place the file on the remote server.
Copy a file from a remote machine to your local machine:
```
 scp -i [Private-Key] [Username]@[Remote-Server-Address]:[Remote-File-Path] [Local-Destination]
```
- [Remote-File-Path] is the file path on the remote server.
- [Local-Destination] is where you want to save the file locally. The dot (.) means the current directory.

Some Useful Commands

Creating and Editing Files:

Create an empty file:
```
 touch [File-Name]
```
For example:
```
 touch myfile.txt
```
Write text to a file:
```
 echo "text to write" > [File-Name]
```
For example:
```
 echo "hello raees" > super_secret.txt
```
This writes "hello raees" into the file super_secret.txt.

Managing Services with Systemctl

Systemctl is used to control and manage services on a server, such as starting, stopping, or checking the status of services.

Basic Systemctl Commands:

Start a service:

 sudo systemctl start [service-name]

Example:

 sudo systemctl start docker

Stop a service:

 sudo systemctl stop [service-name]

Example:

 sudo systemctl stop docker

View logs for a service:

 sudo journalctl -fu [service-name].service

Example:

 sudo journalctl -fu docker.service

Understanding Logs and Searching Through Them

Logs keep track of events, errors, and other important information. You can search and analyze logs using various commands:

Grep:

Search for lines with a specific term:

  grep [search-term] [file-name]

Example:

  grep ERROR app.log

Make the search case-insensitive:
```
  grep -i [search-term] [file-name]
```
Search recursively through directories:
```
  grep -r [search-term] [directory]
```

Find:

Search for files by name:

  find [directory] -name [file-pattern]

Example:

  find /home/ubuntu -name "*.log"

AWK:

Print lines containing a term:
```
  awk '/[search-term]/' [file-name]
```

Print specific columns:

  awk '/[search-term]/ {print $1, $2, $3, $5}' [file-name]

Print row numbers and specific columns:

  awk '/[search-term]/ {print NR, $5}' [file-name]

Sed:

Sed is a stream editor used for modifying files:
- Replace text in a file and save to another file:
```
  sed 's/[old-text]/[new-text]/g' [input-file] > [output-file]
```
  Example:
```
  sed 's/dev+1234/bank+1234/g' dev.env > prd.env
```
  This replaces dev+1234 with bank+1234 and saves the result in prd.env.

Adding Storage to a Server

When your server is running out of space, you can add more storage using EBS (Elastic Block Storage):

Create and attach a new EBS volume to your instance.
Format the new volume:
```
 sudo mkfs -t ext4 /dev/xvdf
```
List block devices:
```
 lsblk
```
Create a mount point:
```
 sudo mkdir /mnt/new_volume
```
Mount the new volume:
```
 sudo mount /dev/xvdf /mnt/new_volume
```

Now, the new storage is ready for use!

Feel free to experiment with these commands and practices to get comfortable with managing files, services, and storage on your server.