Download file via SSH

### Syntax for `scp`

scp [user]@[remote_host]:[remote_path_to_file] [local_path]

### Example
If your remote system details are:
– **Username:** `ubuntu`
– **Host:** `ec2-16-170-254-93.eu-north-1.compute.amazonaws.com`
– **Remote file path:** `/var/www/share/example.txt`
– **Local destination:** `~/Downloads`

Run:

scp ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com:/var/www/share/example.txt ~/Downloads

### Explanation
– `scp`: The command to securely copy files between systems.
– `ubuntu`: The username on the remote system.
– `ec2-16-170-254-93.eu-north-1.compute.amazonaws.com`: The host or IP address of the remote system.
– `/var/www/share/example.txt`: The full path to the file on the remote system.
– `~/Downloads`: The local path where the file will be saved.

### Key Notes
1. **SSH Key**: If the remote system requires an SSH key for authentication, use the `-i` flag to specify the key:

scp -i /path/to/your/private_key.pem ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com:/var/www/share/example.txt ~/Downloads

2. **Password**: If the remote system uses password authentication, you'll be prompted to enter it during the `scp` execution.

3. **Permissions**: Ensure you have the necessary permissions to read the file on the remote system and write to the local directory.

Would you like assistance with uploading a file instead, or do you have specific issues with this approach?

—

### **Steps to Download a File from a Remote SSH Server**

1. **Open the Terminal**:
Press `Ctrl + Alt + T` to open the terminal on your Ubuntu system.

2. **Run the `scp` Command**:
Use the following command to copy the file from the remote server to your Ubuntu system:

scp ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com:/var/www/share/example.txt ~/Downloads

Replace:
– `ubuntu` with your username on the remote server.
– `ec2-16-170-254-93.eu-north-1.compute.amazonaws.com` with the remote server's address.
– `/var/www/share/example.txt` with the file's full path on the remote server.
– `~/Downloads` with the destination folder on your local Ubuntu system.

3. **Authentication**:
– If the remote server uses a password, you will be prompted to enter it after running the command.
– If the server uses an SSH key, you may need to specify the key file using the `-i` flag:

scp -i /path/to/private_key.pem ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com:/var/www/share/example.txt ~/Downloads

4. **Check the File**:
After the transfer is complete, navigate to the destination directory (`~/Downloads` in the example) to confirm the file is there:

ls ~/Downloads

—

### **Troubleshooting**

1. **"Permission Denied" Errors**:
– Ensure your SSH key permissions are correct:

chmod 600 /path/to/private_key.pem

– Verify you have read permissions for the file on the remote server.

2. **Missing `scp` Command**:
If `scp` is not installed, you can install it by installing OpenSSH:

sudo apt update
   sudo apt install openssh-client

3. **Using SSH Passwordless Authentication**:
To simplify repeated transfers, consider setting up SSH keys for passwordless authentication:

ssh-keygen -t rsa
   ssh-copy-id ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com

Would you like help automating this process or configuring SSH keys?

—

### **Example Command**
If you're downloading the file `example.txt` from your remote server, use:

scp ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com:/var/www/share/example.txt ~/Downloads

—

### **Step-by-Step Explanation**
1. **Command Breakdown**:
– `scp`: The command to securely copy files via SSH.
– `ubuntu`: The username on the remote server.
– `ec2-16-170-254-93.eu-north-1.compute.amazonaws.com`: The hostname or IP address of the remote server.
– `/var/www/share/example.txt`: The path to the file on the remote server.
– `~/Downloads`: The destination folder in your local Ubuntu system (`~` points to your home directory).

2. **Check File in Downloads**:
After the transfer, verify the file is in the

—

### **Correct Syntax for `scp`**

To copy the file **`db-2024-11-30.sql`** from a remote server to your local `~/Downloads` directory, the proper command depends on the context.

#### **If the File is on a Remote Server**
If the file is located on a remote server, you should specify the remote path and destination like this:

scp -i /path/to/private_key.pem ubuntu@ec2-16-170-254-93.eu-north-1.compute.amazonaws.com:/path/to/db-2024-11-30.sql ~/Downloads/

Replace:
– `/path/to/private_key.pem`: Path to your private key if required for authentication.
– `ubuntu`: Remote server username.
– `ec2-16-170-254-93.eu-north-1.compute.amazonaws.com`: Remote server hostname or IP.
– `/path/to/db-2024-11-30.sql`: Full path to the file on the remote server.
– `~/Downloads/`: Local destination folder.

—

#### **If the File is on Your Local Machine**
If the file is already on your local machine and you just want to move it to `~/Downloads`, use a simple `mv` command instead:

mv db-2024-11-30.sql ~/Downloads/

—

### **Key Notes**
1. The `-i` flag is **only needed** if you're using an SSH private key for authentication to connect to a remote server.
2. If the file is local, there's no need for `scp`; you can just move or copy it.
3. Ensure the paths (remote and local) are correctly specified.

Let me know if you'd like more help!

—

### **SQL Query**

SELECT 
    table_schema AS database_name,
    table_name,
    ROUND((data_length + index_length) / 1024 / 1024 / 1024, 2) AS size_in_gb
FROM 
    information_schema.tables
WHERE 
    table_schema = 'your_database_name' AND table_name = 'your_table_name';

### **Explanation**
– **`table_schema`**: The name of your database.
– **`table_name`**: The name of your table.
– **`data_length`**: The size of the data stored in the table.
– **`index_length`**: The size of the indexes associated with the table.
– **`ROUND(…, 2)`**: Rounds the size to two decimal places for readability.
– **`/ 1024 / 1024 / 1024`**: Converts bytes to gigabytes (GB).

—

### **Example**
If you want to check the size of a table named `users` in a database called `my_app_db`:

SELECT 
    table_schema AS database_name,
    table_name,
    ROUND((data_length + index_length) / 1024 / 1024 / 1024, 2) AS size_in_gb
FROM 
    information_schema.tables
WHERE 
    table_schema = 'my_app_db' AND table_name = 'users';

This will return the table size in GB.

—

### **For All Tables in a Database**
To see the sizes of all tables in a specific database:

SELECT 
    table_name,
    ROUND((data_length + index_length) / 1024 / 1024 / 1024, 2) AS size_in_gb
FROM 
    information_schema.tables
WHERE 
    table_schema = 'your_database_name'
ORDER BY 
    size_in_gb DESC;

—

### **Output Example**
| database_name | table_name | size_in_gb |
|—————|————|————|
| my_app_db | users | 1.25 |

Would you like assistance running this query or interpreting the results?

—

### **SQL Query to List All Tables in a Database, Ordered by Size**

SELECT 
    table_name,
    ROUND((data_length + index_length) / 1024 / 1024 / 1024, 2) AS size_in_gb
FROM 
    information_schema.tables
WHERE 
    table_schema = 'your_database_name'
ORDER BY 
    size_in_gb DESC;

—

### **Explanation**
– **`table_schema = 'your_database_name'`**: Replace `your_database_name` with the name of your database.
– **`ROUND((data_length + index_length) / 1024 / 1024 / 1024, 2)`**: Calculates the size of each table in GB.
– **`ORDER BY size_in_gb DESC`**: Sorts the tables by size in descending order.

—

### **Example**
For a database named `my_app_db`, the query would be:

SELECT 
    table_name,
    ROUND((data_length + index_length) / 1024 / 1024 / 1024, 2) AS size_in_gb
FROM 
    information_schema.tables
WHERE 
    table_schema = 'my_app_db'
ORDER BY 
    size_in_gb DESC;

—

### **Sample Output**
| table_name | size_in_gb |
|—————-|————|
| large_table | 2.45 |
| medium_table | 0.87 |
| small_table | 0.12 |

—

Would you like additional details, or do you need help exporting this data?

—

### **Why the MySQL Dump is Smaller**
1. **Compression in the Dump Process**:
– The `mysqldump` output is often a plain-text SQL file, which can be much smaller than the raw data because of more efficient text representation.
– Data such as integers or fixed-width fields in the database take up less space in the dump because they are written as plain numbers.

2. **Indexes Are Excluded**:
– `mysqldump` does not include the storage size of indexes (e.g., `INDEX`, `PRIMARY KEY`, etc.) in the dump file, as these are rebuilt when you restore the data.

3. **Storage Engine Overhead**:
– Storage engines like InnoDB add metadata and overhead for things like row pointers and transaction logs. This overhead isn't part of the SQL dump.

4. **Unused Space**:
– Databases may have unused or fragmented space due to updates and deletes. These aren't part of the dump but contribute to the table size reported by MySQL.

5. **Binary Data**:
– If the table contains binary data, it may be encoded differently in the dump, which could reduce the size.

—

### **Steps to Analyze the Difference**

#### 1. **Check Actual Data Size**
Use the following query to check the data size and index size for the table:

SELECT 
    table_name, 
    ROUND(data_length / 1024 / 1024, 2) AS data_size_mb,
    ROUND(index_length / 1024 / 1024, 2) AS index_size_mb,
    ROUND((data_length + index_length) / 1024 / 1024, 2) AS total_size_mb
FROM 
    information_schema.tables
WHERE 
    table_schema = 'your_database_name' 
    AND table_name = 'your_table_name';

This will help you understand how much of the 7GB size is due to indexes or data.

—

#### 2. **Inspect Dump File Compression**
If you suspect compression was applied during the dump, check the file with:

file dumpfile.sql

If it reports `gzip compressed data` or similar, decompress the file first:

gunzip dumpfile.sql.gz

—

#### 3. **Include Indexes in Size Analysis**
To rebuild indexes during the dump (which slightly increases the dump size):

mysqldump --no-create-info --extended-insert --add-drop-table --all-databases > dumpfile.sql

—

#### 4. **Export with Raw Data**
If you want a dump that is closer in size to the actual table, you can use `SELECT INTO OUTFILE` to export the raw table data:

SELECT * 
INTO OUTFILE '/path/to/outputfile.csv' 
FIELDS TERMINATED BY ',' 
ENCLOSED BY '"' 
LINES TERMINATED BY 'n'
FROM your_table_name;

—

### **Recommendation**
– **Smaller dump sizes are normal** for plain-text dumps as they don't include overhead like indexes and metadata.
– If the size difference concerns you, double-check the integrity of the data by restoring the dump in a test environment and verifying the table content.

Would you like help analyzing the restored dump or exploring the table's content?