CE47 month 2 linux lesson 5 6 p2

Main ideas / lessons

• Linux file/directory permissions control who can do three actions on something (file or directory):

  • Read (r): view/open the contents of a file (or list/read a directory’s contents).
  • Write (w): modify/create/delete contents within the file/directory (for directories, it controls adding/removing entries).
  • Execute (x): run/enter:
    • For files: opening/running a program (or “executing” a script).
    • For directories: entering the directory (traversing into it) and later exiting.

• Permissions are expressed in two equivalent ways:

  1. Letters: rwx patterns.
  2. Numbers (octal): a compact form derived from the rwx set.

• Permission targets are in three categories (in the common display order):

  1. User (owner) — “u”
  2. Group — “g”
  3. Others — “o” (everyone not in the user/group)

• The ls -l output structure includes:

  • A leading indicator for type:
    • d means directory
    • otherwise it’s a file
  • Then the permissions are shown as three rwx blocks: user, group, others.

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Methodology / instruction list (Change Mode: chmod)

1) Use chmod to set permissions

• The tool referenced is change mod, i.e. chmod.
• You can set permissions using either:
  • letters form (easier conceptually), or
  • numbers form (more convenient/short).

2) Meaning of numeric permissions (the core rule)

• Each permission corresponds to a value:
  • Read (r) = 4
  • Write (w) = 2
  • Execute (x) = 1
• For each category (user / group / others), you add the values of the permissions you want.

Example conversions

• 7 means 4+2+1 → rwx (read + write + execute)
• 6 means 4+2 → rw- (read + write, no execute)
• 5 means 4+1 → r-x (read + execute, no write)
• 4 means r-- (read only)
• 3 means 2+1 → -wx (write + execute, no read)
• 2 means -w- (write only)
• 1 means --x (execute only)
• 0 means --- (no permissions)

3) Numeric chmod syntax (as shown conceptually)

• Apply permissions as a 3-digit number:
  • chmod USERGROUPOTHER (where each digit maps to one category)
• The intended idea:
  • first digit → user
  • second digit → group
  • third digit → others

Examples mentioned (conceptually):

• chmod 711 ...
• chmod 731 ...
• chmod 755 ...
• chmod 761 ...
• chmod 444 ...
• chmod 426 ...

4) Letter-based chmod syntax (as described)

• Use the who specifiers:
  • u = user/owner
  • g = group
  • o = others
• Use the permission set specifiers:
  • r, w, x
• Example conceptually described:
  • “give the user rwx, give group r-x, give others --x”, etc.
• The subtitles also mention chmod “with letters,” likely implying formats like:
  • chmod u=rwx,g=...,o=... <target>

5) Permission behavior for directories vs files

• Directories: execute (x) means you can enter/access the directory
  • You may be able to go in and out, but other permissions decide whether you can create/modify/list contents.
• Files: execute (x) means run the program/script
  • Read/write decide view/modify.

6) How to create files for practice

• The class uses touch to create files.
• Practice includes creating multiple files (e.g., “file one…file five”, eventually “10 files” as homework).

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Key conceptual examples used in the lesson (explained)

• Default installed folder example (described):

  • Directories show d in ls -l.
  • Some folders are set so:
    • users can read/write/execute
    • groups may have read/execute
    • others may only read/execute or only execute depending on the scenario described.

• Group-based permission rationale (why you set group permissions):

  • If you create a file/folder as a user in group C46, you might want:
    • your user to have full access (r/w/x)
    • your group members to have write/read access
    • members of other groups to have only limited access (often just execute so they can enter/look but not modify)
  • The lesson uses a “TV / remote control” analogy:
    • Owner can fully control (plug/unplug; “execute” conceptually ties to full capability)
    • Group can change/view depending on permissions (read/write)
    • Others can mainly view/enter, but not the modification capability (no execute/write as appropriate)

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Practice / homework workflow (as conveyed)

• In-class practice:

  • Create multiple files using touch.
  • Run ls -l to confirm permission bits.
  • Apply different permission sets using chmod with numbers or letters.
  • Check correctness by comparing ls -l output to the intended rwx mapping.

• Homework stated at the end:

  • Create 10 files and assign different permission schemes (the instructor says homework is related to permissions).

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Speakers / sources featured

Instructors / speakers (named in subtitles)

• Teacher (referred to as “teacher” / also “Krosh” in subtitles)
• Hüseyin
• Javidan
• Nurlan
• Cavidan
• “Hussein” / “Hüseyin” (same person, inconsistent spelling)
• Krosh (another participant referred to like a student/teammate; also used as a name)
• Discord (mentioned as the environment/platform where the students are participating)

External sources

• No external sources (like websites/books) are clearly identified in the subtitles.