Chmod Calculator
Convert Linux file permissions between octal (755) and symbolic (rwxr-xr-x) form, with per-class read/write/execute breakdown and special bits.
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What this tool does
Convert Linux file permissions between octal (755) and symbolic (rwxr-xr-x) form, with per-class read/write/execute breakdown and special bits. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
How to use the Chmod Calculator
- Enter or select convert from.
- Enter or select octal permissions.
- Enter or select owner permissions.
- Enter or select group permissions.
- Enter or select other permissions.
- Read the calculated result; change any measurement to compare alternatives.
Formula
Each octal digit sums read (4) + write (2) + execute (1) for one class: owner, group, other. A leading fourth digit sums setuid (4), setgid (2) and sticky (1).
- source
- Convert from
- octal
- Octal permissions
- owner
- Owner permissions
- group
- Group permissions
- other
- Other permissions
Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
Worked example
For chmod calculator, the following measurements illustrate the exact method: Convert from: octal; Octal permissions: 755; Owner permissions: 7; Group permissions: 5; Other permissions: 5.
Inputs
- Convert fromOctal number (e.g. 755)
- Octal permissions755
- Owner permissionsrwx (7)
- Group permissionsr-x (5)
- Other permissionsr-x (5)
Result
- Symbolic permissionsrwxr-xr-x
- Octal755
- Ownerrwx
- Groupr-x
- Otherr-x
- Special bitsNone
- chmod commandchmod 755 <file>
Results explained
- Symbolic permissions
- Symbolic permissions from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
- Octal
- Octal from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
- Owner
- Owner from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
- Group
- Group from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
- Other
- Other from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
- Special bits
- Special bits from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
- chmod command
- chmod command from the formula above. Covers the standard 3-class permission model plus special bits. It does not model ACLs, filesystem mount options or umask interaction — the mode you set is the mode requested, before any umask is applied at creation time.
Frequently asked questions
Owner can read, write and execute (7 = 4+2+1 = rwx); group and others can read and execute (5 = 4+1 = r-x). Symbolic form: rwxr-xr-x. It is the standard mode for executables and web directories.
Add 4 for read, 2 for write and 1 for execute per class. Read-only is 4, read+write is 6, read+execute is 5, and full access is 7. Three digits cover owner, group and others in that order.
A fourth leading digit: setuid (4) runs an executable as its owner, setgid (2) as its group (or inherits the directory's group), and sticky (1) on a directory like /tmp stops users deleting each other's files. They appear as s/s/t in symbolic output.
600 (rw-------) for private files like SSH keys — SSH refuses keys with looser permissions. 644 (rw-r--r--) is the usual choice for shareable read-only content.
On directories, execute means 'traverse' — without it you cannot open files inside even if you can list names (read). That is why web directories are typically 755, not 744.