Linux permissions tools

Chmod calculator for existing permissions and umask calculator for the defaults of new files. All in the browser.

Who this collection is for

For system administrators, DevOps teams, IT support, developers who touch permissions occasionally and students learning the POSIX model without breaking their workstation. It covers the two classic tasks: turning 755 / 644 / 750 into real meaning (chmod) and predicting which permissions future files and directories will get (umask).

Every calculation runs entirely in your browser. We do not upload values to any server: the code contains no remote endpoint that ships your input. Both tools are teaching and verification utilities; they do not apply changes to the system — they produce the command or value you can then run yourself.

From the current permission to the future permission

Three steps that show up when auditing or configuring permissions on a Linux box:

1.Audit what is already there
Start from the octal or symbolic value that `ls -l` shows and use the chmod calculator to understand what it allows. Spot dangerous combinations (world-writable scripts, SSH keys that are too open, setuid in odd places).
2.Define the policy for what comes next
For files and directories created from now on, set the user's or service's umask: 022 as a sensible default, 027 if you want to hide content from non-group users, 077 for processes whose data must not be touched by anyone else.
3.Document the command you will apply
Both chmod and umask produce a command or a shell-ready value. Use the copy buttons to drop it into a runbook, a ticket or the matching config file (~/.bashrc, /etc/profile, systemd unit with UMask=).

Tools in this collection

The two utilities that cover that workflow today. Both run without routing your data through a backend.

chmod calculator — octal permissions 755, 750 and 765

Chmod calculator for existing POSIX permissions: octal ↔ symbolic ↔ ls -l line, setuid/setgid/sticky support, risk engine and shareable URL state.

Turn 755, 750, 644, 4755… into real meaning on files and directories.
Flag dangerous combinations (world-writable scripts, open SSH keys).
Produce the chmod command ready to copy.

Open the chmod calculator →

Umask calculator — default Linux permissions

Umask calculator: which permissions new files and directories will have given a specific umask. 022, 027, 077, 002… with octal and symbolic output.

Apply 666 & ~umask for files and 777 & ~umask for directories.
Tell apart file defaults and directory defaults (not the same).
Recommend a umask by scenario: server, personal profile, group collaboration.

Open the umask calculator →

Which tool to use

Quick decisions based on the problem you have in front of you.
Your situation	Tool
I have 755, 644 or 750 and want to understand what it allows	chmod
I need to convert rwxr-xr-x to octal or the other way round	chmod
I want to know what umask 022 creates for files and directories	umask
I want to configure defaults for the service's future files	umask
I need to change permissions on a file that ALREADY exists	chmod (umask does not touch existing files)
I want long-term permissions policy on the server	umask + chmod (one sets defaults, the other corrects exceptions)

Quick cheatsheet

r=4, w=2, x=1: Every chmod bit sums: read 4, write 2, execute 1. Range 0-7 per audience (owner, group, others). 7 = rwx, 5 = r-x, 4 = r--.
Common chmod modes: 755 (scripts and public directories), 750 (team-only), 700 (owner-private), 644 (readable files), 640 (server-restrictive), 600 (secrets).
Common umasks: 022 (sensible default), 027 (stricter for servers), 077 (user-private), 002 (group collaboration).
File vs directory: The base modes differ: files start from 666 (no execute) and directories from 777. For the same umask 022 you get 644 on files and 755 on directories.
Setuid, setgid, sticky: Special leading bits: 4 setuid (run as owner), 2 setgid (inherit group), 1 sticky (only owner can delete). Example: 1777 = directory with sticky bit (/tmp).

Go deeper

The cluster's editorial guides cover both sides: chmod fixes permissions on existing files, and umask defines the default permissions new files and directories receive. Remember umask does NOT modify existing files — it only affects what gets created after its configuration.