Linux CLI 17 🐧 Owner, group member and the rest - KandZ

Every file and directory in Linux has permissions that control who can do what. Understanding permissions is essential for security and collaboration.

Reading `ls -l` Output

$ ls -l
-rw-r--r--  1 kronos users  1024 Jan 15 10:30 1.txt
drwxr-xr-x  2 kronos users  4096 Jan 15 10:30 d2

Let’s break down each column:

-rw-r--r--  1 kronos users  1024 Jan 15 10:30 1.txt
│           │ │      │      │    │           │
│           │ │      │      │    │           └── Filename
│           │ │      │      │    └────────────── Last modification date
│           │ │      │      └─────────────────── File size (bytes)
│           │ │      └────────────────────────── Group
│           │ └───────────────────────────────── Owner
│           └─────────────────────────────────── Hard links count
└─────────────────────────────────────────────── File type + permissions

File Type — The First Character

Character	Type	Example
`-`	Regular file	`-rw-r--r--`
`d`	Directory	`drwxr-xr-x`
`l`	Symbolic link	`lrwxrwxrwx`
`c`	Character device	`crw-rw-rw-`
`b`	Block device	`brw-rw----`
`p`	Pipe (FIFO)	`prw-r--r--`
`s`	Socket	`srwxrwxrwx`

Examples:

-rw-r--r--   regular file
drwxr-xr-x   directory
lrwxrwxrwx   symbolic link
crw-rw-rw-   character device (e.g., /dev/tty)
brw-rw----   block device (e.g., /dev/sda)
prw-r--r--   named pipe
srwxrwxrwx   socket

The Three Permission Groups

The next 9 characters (positions 2–10) are divided into three groups of three:

-  rw-  r--  r--
│  │    │    │
│  │    │    └── Permissions for the "rest" (others)
│  │    └─────── Permissions for group members
│  └──────────── Permissions for the owner
└─────────────── File type

Group	Characters	Applies To
1st group	2, 3, 4	Owner’s permissions
2nd group	5, 6, 7	Group members’ permissions
3rd group	8, 9, 10	Everyone else (the rest)

The Three Permission Types

Within each group of three:

r w x
│ │ │
│ │ └── x = execute permission
│ └──── w = write permission
└────── r = read permission

Position	Symbol	Meaning
1st	`r`	Read permission
2nd	`w`	Write permission
3rd	`x`	Execute permission
Missing	`-`	No permission

What Each Permission Means

Permission	On a File	On a Directory
r (read)	View file contents	List directory contents (`ls`)
w (write)	Modify file contents	Create/delete files in directory
x (execute)	Run file as program	Enter the directory (`cd`)

Important: x on a directory means you can enter it with cd. Without x, you can’t cd into it — even if you have r.

Example Analysis

Example 1: `1.txt` — A Regular File

-rw-r--r--  1 kronos users  1024 Jan 15 10:30 1.txt

Breaking it down:

-  rw-  r--  r--
│  │    │    │
│  │    │    └── Rest: read only
│  │    └─────── Group: read only
│  └──────────── Owner: read and write
└─────────────── Regular file

Who	Permissions	Meaning
Owner	`rw-`	Can read and write (modify)
Group	`r--`	Can only read
Rest	`r--`	Can only read

Owner: kronos — the user who owns the file
Group: users — the group the file belongs to

What each can do:

kronos (owner): Read the file, edit it, but cannot execute it
Group members: Only read the file
Others: Only read the file

Example 2: `d2` — A Directory

drwxr-xr-x  2 kronos users  4096 Jan 15 10:30 d2

Breaking it down:

d  rwx  r-x  r-x
│  │    │    │
│  │    │    └── Rest: read and enter
│  │    └─────── Group: read and enter
│  └──────────── Owner: read, write, and enter
└─────────────── Directory

Who	Permissions	Meaning
Owner	`rwx`	Can list, modify (create/delete), and enter
Group	`r-x`	Can list and enter, but not modify
Rest	`r-x`	Can list and enter, but not modify

What each can do:

kronos (owner): Full control — cd in, ls, create/delete files
Group members: Enter the directory, see contents, but can’t add/remove files
Others: Same as group — can look but not touch

Who Owns What?

Term	Meaning	Example
Owner	The user who owns the file	`kronos`
Group	The group that owns the file	`users`
Rest	Everyone else on the system	—

Visual:

┌────────────────────────────────────────────────┐
│                    System                      │
│                                                │
│  ┌──────────────┐  ┌──────────────┐  ┌────────┐│
│  │    Owner     │  │    Group     │  │  Rest  ││
│  │   kronos     │  │    users     │  │ Others ││
│  │              │  │              │  │        ││
│  │  rw- (rwx)   │  │  r-- (r-x)   │  │ r--    ││
│  └──────────────┘  └──────────────┘  └────────┘│
└────────────────────────────────────────────────┘

Common Permission Combinations

Permissions	Symbolic	Octal
`rwxrwxrwx`	`777`	Everyone: full access
`rwxr-xr-x`	`755`	Owner: full; others: read+execute
`rw-r--r--`	`644`	Owner: read+write; others: read
`rwx------`	`700`	Owner only: full access
`rw-------`	`600`	Owner only: read+write
`rwxr-x---`	`750`	Owner: full; group: read+execute
`rw-rw-r--`	`664`	Owner+group: read+write; others: read
`rwxrwx---`	`770`	Owner+group: full; others: none

Octal (Numeric) Permissions

Each permission type has a numeric value:

Permission	Value
`r` (read)	4
`w` (write)	2
`x` (execute)	1
`-` (none)	0

Add them up per group:

Permission	Calculation	Octal
`rwx`	4 + 2 + 1	7
`rw-`	4 + 2 + 0	6
`r-x`	4 + 0 + 1	5
`r--`	4 + 0 + 0	4
`-wx`	0 + 2 + 1	3
`-w-`	0 + 2 + 0	2
`--x`	0 + 0 + 1	1
`---`	0 + 0 + 0	0

Example:

-rw-r--r--   →   6 4 4   →   644
drwxr-xr-x   →   7 5 5   →   755
-rwxr-x---   →   7 5 0   →   750

Complete Example Session

# ============================================
# PART 1: READING LS -L OUTPUT
# ============================================

$ ls -l
-rw-r--r--  1 kronos users  1024 Jan 15 10:30 1.txt
drwxr-xr-x  2 kronos users  4096 Jan 15 10:30 d2
lrwxrwxrwx  1 kronos users    10 Jan 15 10:30 link -> /etc
crw-rw-rw-  1 root   root   1, 3 Jan 15 10:30 /dev/null
brw-rw----  1 root   disk   8, 0 Jan 15 10:30 /dev/sda

# ============================================
# PART 2: ANALYZING PERMISSIONS
# ============================================

# File: 1.txt — regular file
# Owner: kronos — read, write
# Group: users — read
# Rest: read
-rw-r--r--  1 kronos users  1024 Jan 15 10:30 1.txt

# Directory: d2
# Owner: kronos — read, write, enter
# Group: users — read, enter
# Rest: read, enter
drwxr-xr-x  2 kronos users  4096 Jan 15 10:30 d2

# ============================================
# PART 3: PERMISSION MEANING
# ============================================

# For 1.txt:
# Owner kronos: can read and write
# Group users: can read only
# Others: can read only
# Nobody can execute

# For d2 (directory):
# Owner kronos: can cd in, ls, create/delete files
# Group users: can cd in, ls, but not create/delete
# Others: same as group

# ============================================
# PART 4: PRACTICAL EXAMPLES
# ============================================

# A private file — only owner can read/write
-rw-------  1 kronos users  1024 Jan 15 10:30 private.txt

# A shared file — owner and group can read/write
-rw-rw-r--  1 kronos developers  1024 Jan 15 10:30 shared.txt

# An executable script
-rwxr-xr-x  1 kronos users  2048 Jan 15 10:30 script.sh

# A web file — readable by everyone
-rw-r--r--  1 root   root   4096 Jan 15 10:30 /var/www/index.html

# A secret directory — only owner
drwx------  2 kronos users  4096 Jan 15 10:30 .ssh

Quick Reference

File Types (First Character)

Symbol	Type
`-`	Regular file
`d`	Directory
`l`	Symbolic link
`c`	Character device
`b`	Block device
`p`	Pipe
`s`	Socket

Permission Groups

Group	Positions	Applies To
1st	2, 3, 4	Owner
2nd	5, 6, 7	Group members
3rd	8, 9, 10	The rest (others)

Permission Types

Symbol	Name	Value	On File	On Directory
`r`	Read	4	View contents	List contents
`w`	Write	2	Modify contents	Create/delete files
`x`	Execute	1	Run program	Enter with `cd`
`-`	None	0	No access	No access

Common Octal Values

Octal	Symbolic	Meaning
`644`	`rw-r--r--`	Owner: rw; others: r
`755`	`rwxr-xr-x`	Owner: rwx; others: rx
`700`	`rwx------`	Owner only
`600`	`rw-------`	Owner only (files)
`664`	`rw-rw-r--`	Owner+group: rw
`777`	`rwxrwxrwx`	Everyone: rwx (rarely needed)

Best Practices

✅ Do This:

# Files — 644 (rw-r--r--) is the safe default
chmod 644 file.txt

# Directories — 755 (rwxr-xr-x) is the safe default
chmod 755 mydir

# Private files — 600 (rw-------) for sensitive data
chmod 600 ~/.ssh/id_rsa
chmod 600 .env

# Private directories — 700 (rwx------)
chmod 700 ~/.ssh

# Executables — 755 (rwxr-xr-x)
chmod 755 script.sh

❌ Don’t Do This:

# Don't give everyone everything
chmod 777 file.txt       # ❌ Security risk!
chmod -R 777 /var/www    # ❌ Very dangerous!

# Don't remove execute from directories
chmod -x mydir           # ❌ Can't cd into it

# Don't make scripts non-executable and expect them to run
chmod 644 script.sh
./script.sh              # ❌ Permission denied
chmod +x script.sh       # ✅ Fix

# Don't share sensitive files with group/others
chmod 644 ~/.ssh/id_rsa  # ❌ Private key should be 600!

Common Pitfalls

Pitfall	Problem	Solution
`x` on directory	Needed to `cd` in	Keep `x` on directories
Files without `r`	Can’t read	Add `r`
Scripts without `x`	Can’t execute	`chmod +x script.sh`
Everyone can read	Security risk	Use `600` for private
Confusing owner/group	Wrong access	Check with `ls -l`
`777` on web files	Wide open to attacks	Use `644` for files, `755` for dirs

Real-World Examples

1. Web Server Files

# HTML files — owner write, all read
-rw-r--r--  1 www-data www-data  index.html

# Directories — owner full, all enter+list
drwxr-xr-x  2 www-data www-data  uploads/

# Never use 777!

2. SSH Keys

# Private key — owner only
-rw-------  1 kronos users  id_rsa

# Public key — readable by all
-rw-r--r--  1 kronos users  id_rsa.pub

# SSH directory — owner only
drwx------  2 kronos users  .ssh/

3. Shared Development

# Team-shared project — group can write
drwxrwxr-x  5 alice developers  project/
-rw-rw-r--  1 alice developers  README.md

4. System Binaries

# Executables — everyone can run
-rwxr-xr-x  1 root root  /usr/bin/ls
-rwxr-xr-x  1 root root  /bin/bash

Visual: Permission Structure

-rw-r--r--  1 kronos users  1024 Jan 15 10:30 1.txt
│└┬┘└┬┘└┬┘
│ │  │  └── Rest: read only
│ │  └───── Group: read only
│ └──────── Owner: read + write
└────────── Regular file

POSITIONS:
  1    2 3 4    5 6 7    8 9 10
  │    │  │  │    │  │  │    │  │  │
  │    r  w  -    r  -  -    r  -  -
  │    └──┬──┘    └──┬──┘    └──┬──┘
  │       │          │          │
  │    Owner       Group      Rest
  │
  File type (- = file, d = directory)

Summary

Concept	Description
First character	File type (`-`, `d`, `l`, etc.)
Positions 2–4	Owner permissions
Positions 5–7	Group permissions
Positions 8–10	Others permissions
r	Read (4)
w	Write (2)
x	Execute/Enter (1)
–	No permission (0)

Key takeaways:

ls -l shows permissions in a 10-character string
First character = file type
Next 9 characters = permissions in three groups (owner, group, rest)
Each group has three permissions: read (r), write (w), execute (x)
x on a directory means you can cd into it
x on a file means you can run it as a program
Permission values are summed: r=4, w=2, x=1
644 = files (owner rw, others r)
755 = directories/executables (owner rwx, others rx)
600 = private files (owner only)
777 = dangerous — avoid at all costs

Remember: Permissions control who can do what. The three groups — owner, group, rest — let you set fine-grained access. Use 644 for regular files, 755 for directories and executables, and 600 for sensitive data. Never use 777 — it’s a security hole. And always think: who needs to read this? Who needs to write this? Who needs to execute this?

Stop using slow, ad-bloated tool sites! 🤮

🔎 Search “KandZ Tools” on Google to use many professional utilities for free.

KandZ.me is the ultimate minimalist hub for:
✅ Finance (Mortgage, Interest, Inflation)
✅ Tech (Base64, JSON, Dev Suite, IP)
✅ Health (BMI, BMR, TDEE)
✅ Productivity (Timer, Workspace, QR)

⚡️ Fast & Private
🔒 No data leaves your device
💎 100% Free

🔗 Use it now: https://tools.kandz.me
🔖 Bookmark it—you’ll need it later!

Reading ls -l Output