In the world of system administration, efficiency and reliability are paramount. One of the most powerful tools in a sysadmin's arsenal is shell scripting. With just a few lines of code, routine tasks can be automated, freeing up valuable time and reducing the risk of human error. In this blog post, we'll explore three essential concepts in shell scripting: taking backups, scheduling tasks with cron jobs, and real-time monitoring using the watch command.

Taking Backups

Backups are a crucial aspect of system administration, ensuring that critical data is protected against loss or corruption. In shell scripting, creating a backup script can be surprisingly straightforward. Here's a basic example using the tar command to create a gzip compression of a directory:

#!/bin/bash

#backup concept 

src_dir="/home/ubuntu/scripts"
tgt_dir="/home/ubuntu/backups"
backup_filename="backup_$(date +%Y-%m-%d-%H-%M-%S).tar.gz"
echo "Backup started"
echo  "backing up to $backup_filename"
 tar -czvf "${tgt_dir}/${backup_filename}" "$src_dir"
 echo "Backup completed"
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tar Command to Compress Files

The Linux ‘tar’ stands for tape archive, which is used to create Archive and extract the Archive files. tar command in Linux is one of the important commands that provides archiving functionality in Linux. We can use the Linux tar command to create compressed or uncompressed Archive files and also maintain and modify them.

Syntax of tar command in Linux

tar [options] [destination] [source]

• tar: The command itself.

• [options]: Optional flags or settings that modify the behavior of the tar command.

• [destination]: The name of the archive file you are creating or working with.

• [Source]: The file or directory you want to include in the archive.

  An Archive file is a file that is composed of one or more files along with metadata. Archive files are used to collect multiple data files together into a single file for easier portability and storage, or simply to compress files to use less storage space.

  | Options | Description | | --- | --- | | -c | Creates an archive by bundling files and directories together. | | -x | Extracts files and directories from an existing archive. | | -f | Specifies the filename of the archive to be created or extracted. | | -t | Displays or lists the files and directories contained within an archive. | | -u | Archives and adds new files or directories to an existing archive. | | -v | Displays verbose information, providing detailed output during the archiving or extraction process. | | -A | Concatenates multiple archive files into a single archive. | | -z | Uses gzip compression when creating a tar file, resulting in a compressed archive with the ‘.tar.gz’ extension. | | -j | Uses bzip2 compression when creating a tar file, resulting in a compressed archive with the ‘.tar.bz2’ extension. | | -W | Verifies the integrity of an archive file, ensuring its contents are not corrupted. | | -r | Updates or adds files or directories to an already existing archive without recreating the entire archive. |

  Scheduling Tasks with Cron Jobs

  Cron is a time-based job scheduler in Unix-like operating systems, used to schedule commands or scripts to run periodically at fixed times, dates, or intervals. Cron jobs are defined in crontab files, and managing them effectively can simplify system maintenance. Here's how you can schedule the backup script to run daily at midnight:

    #crontab file for editing
    crontab -e
  
    # Add the following line to schedule the backup script
    0 0 * * * /path/to/backup_script.sh
  

  This line specifies that the backup script should run at 12:00 AM (midnight) every day. Adjust the timing as needed to suit your requirements.

  Real-Time Monitoring with watch Command

  The watch command is a useful tool for real-time monitoring of command output. It runs a specified command repeatedly at regular intervals and displays the results on the terminal. For example, you can use watch to monitor changes in a directory using the ls command:

    watch -n 2 ls /path/to/directory
  

  This command will continuously display the contents of the specified directory, updating every 2 seconds by default. It's particularly handy for monitoring log files, system resources, or any other command output that changes over time.