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Day 4
Setting Executable Permissions on a Script


I was tasked with making a shell script executable, as the system required the necessary permissions to run the new backup script.

Table of Contents



The Task

The task involved granting executable permissions to a bash script named xfusioncorp.sh on App Server 2 and ensuring all system users could execute it.



My Solution & Command Breakdown

- After connecting to App Server 2, I first checked the existing permissions and then used a single command to change them.

1. The Verification Command (Before)

  • I used ls -l to get a detailed listing of the file.
ls -l /tmp/xfusioncorp.sh

# OUTPUT:
# -rw-r--r-- ...   -> confirmed that no one had execute (`x`) permissions.

2. The Permission Change Command

I used the chmod (change mode) command to add the necessary permissions.

sudo chmod a+x /tmp/xfusioncorp.sh

Command Breakdown: * chmod: The main command used to change file permissions. * a+x: A symbolic way to add execute permission: * a: all users (owner, group, others) * +: add permission * x: execute permission

3. The Verification Command (After)

I ran the ls -l command again to confirm my change was successful. 

ls -l /tmp/xfusioncorp.sh

# OUTPUT:
# -rwxr-xr-x ...



Why Did I Do This? (The "What & Why")

This task is all about telling the operating system that a file is not just data to be read, but a program that can be run.

  • Security: By default, new files aren’t executable. This prevents random or downloaded files from running automatically, keeping the system safe. Linux makes sure only trusted scripts or programs can run.

  • Operational Need: Automation scripts need execute permission to work. In this case, the backup system (and admins testing it) must be able to run the script. Without +x, the system would block it with a “Permission Denied” error, even if the script is correct.



Deep Dive: Understanding Linux File Permissions

A permission string like -rwxr-xr-x has four parts: - File Type → The first character shows the type: - = regular file, d = directory. - Owner Permissions → Next three (rwx) are for the owner: read, write, execute. - Group Permissions → Next three (r-x) are for the group: read and execute, but no write. - Other Permissions → Last three (r-x) are for everyone else: read and execute, but no write.

Two common ways to set permissions:

  • Symbolic Notation → Human-readable like a+x (all users add execute), u+x(user add execute), g+w (group add write), o-r (others remove read).
  • Octal/ Numeric Notation → Each permission has a number: read=4, write=2, execute=1. Add them for each category:
  • Owner rwx = 4+2+1 = 7
  • Group r-x = 4+0+1 = 5
  • Others r-x = 4+0+1 = 5 So sudo chmod 755 /tmp/xfusioncorp.sh does the same as setting rwxr-xr-x.



Exploring the Commands Used

This task introduced me to two of the most frequently used commands in Linux.

  • chmod: Stands for change mode. It’s the main command to modify file or directory permissions. Learning both symbolic and octal ways to use it is very useful.
  • ls -l: Lists files in long format. Shows not just filenames, but also permissions, owner, group, size, and last modified date. Essential for checking and troubleshooting permissions.