In Linux and Unix-like operating systems, file permissions determine who can read, write, or execute files. The chmod (change mode) command alters these permissions using either octal numbers (e.g. 755) or symbolic modifier strings (e.g. u+rwx).
Use this interactive calculator to toggle modes, build octal codes, or generate relative symbolic modifiers to run in your console.
Interactive Calculator
[ CHMOD CALCULATOR ]
Class
Read (4)
Write (2)
Execute (1)
User (Owner)
Group
Others
Symbolic String:-rwxr-xr-x
Octal Notation:755
Terminal Command:
chmod 755 filename
[INFO]Calculating privileges...
[ ACCESS CAPABILITY MATRIX ]
Action
Owner
Group
Others
Read File / List Dir (r)
Yes
Yes
Yes
Modify File / Write Dir (w)
Yes
No
No
Execute File / Enter Dir (x)
Yes
Yes
Yes
1. Target Class:
2. Operation:
3. Permissions:
Symbolic Modifier:u+rx
Terminal Command:
chmod u+rx filename
[INFO]Calculating modifier...
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### What Do the Numbers Mean?
In Linux, file permissions are managed using three octal digits representing three access classes:
1. **First Digit:** Owner permissions.
2. **Second Digit:** Group permissions.
3. **Third Digit:** Others permissions.
To calculate each digit, you add up the values of the permissions granted:
* **Read (r):** `4`
* **Write (w):** `2`
* **Execute (x):** `1`
* **No Permission (-):** `0`
For example:
* `Read` + `Write` + `Execute` = `4 + 2 + 1 = 7`
* `Read` + `Execute` = `4 + 0 + 1 = 5`
* `Read` only = `4 + 0 + 0 = 4`
Therefore, `755` grants the owner full control (`7`), and lets group members and everyone else read and execute files (`5`) but not modify them.
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### Common Configurations Quick Reference
* `755` - **Standard executable file:** Owner can modify/execute; everyone else can read/execute. Useful for scripts.
* `644` - **Standard text file:** Owner can modify; everyone else can only read. Safe default for configs, HTML, and assets.
* `700` - **Private script/keys:** Only the owner can access or run. Excellent for SSH key folders (`~/.ssh`) or private logs.
* `600` - **Private configuration:** Only the owner can read or write (e.g. private SSH keys like `id_rsa`).