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In this lesson, we’ll explore how to view and modify file permissions and ownership on a Linux system. You’ll learn to inspect permission bits, change owners and groups, and apply both symbolic and numeric modes with chmod, chown, and chgrp.

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Inspect Current Ownership and Permissions

Run ls -l to display the owner, group, and permission bits for files and directories:
  • Owner: aaron
  • Group: family
  • Permissions: -rw-r-----
Only the file owner or the superuser (root) can change these settings.

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Viewing and Changing Group Ownership

Use chgrp to assign a file or directory to a different group you belong to:
Check your group memberships with:
You can only switch a file’s group to one you’re already a member of.

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Changing File Owner with chown

Only root can change file owners. Prefix with sudo if necessary:

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Understanding Permission Bits

The permissions string (-rwxrwxrwx) breaks down as:
  • First character: file type
    • - = regular file
    • d = directory
    • l = symbolic link
  • Next nine: three triplets for owner, group, and others, each with r (read), w (write), and x (execute).
The image illustrates file and directory permissions in a Unix-like system, showing the permission string "rwxrwxrwx" for owner, group, and others, along with a key explaining the meaning of each permission bit.

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Permission Effects

  • Files
    • r: view contents
    • w: modify contents
    • x: execute (scripts or binaries)
  • Directories
    • r: list entries (ls)
    • w: create/delete entries
    • x: enter directory (cd)

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Modifying Permissions with chmod

Use the symbolic syntax:

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Adding Permissions

Allow the owner to write:

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Removing Permissions

Remove the read bit for others:
The image shows a guide on removing permissions in a command-line interface, with examples for users, groups, and others. It includes options like u-, g-, and o- with examples such as u-w, g-rw, and o-rwx.

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Setting Exact Permissions

Grant group read-only:

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Combining References

You can comma-separate multiple adjustments:

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Numeric (Octal) Notation

To inspect the octal value, use stat:
Here owner has rw- (6), group has r-- (4), others have --- (0) → mode 640.
The image illustrates octal file permissions, showing the conversion between symbolic, binary, and decimal representations. It includes examples of permissions like "rw-r--r--" and "rwxr-xr-x" with their corresponding binary and decimal values.
Alternatively, assign values: r=4, w=2, x=1:
  • rwx = 4+2+1 = 7
  • r-x = 4+0+1 = 5
  • r-- = 4+0+0 = 4
The image explains octal permissions in a Unix-like system, showing how the permissions "rw-r-----" translate to the octal value "640". It also provides a key for permission values: read (r) is 4, write (w) is 2, and execute (x) is 1.

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Setting Numeric Permissions

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Further Reading

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