Terminal & DevOps
Chmod Calculator & Linux Permissions Generator
Interactive chmod calculator and command builder. Convert between octal and symbolic Linux file permissions, understand user/group/other rights, and export shell commands.
Type any octal (e.g. 755, 644, 700) to update the matrix.
-rwxr-xr-x
Permissions Matrix
Owner (User)7
Group5
Others (Public)5
Special Flags (Optional)
Ready-to-Run Shell Command
chmod 755 script.shCommon Linux Permission Presets
Advertisement
How to use
- 1Click any checkbox in the Owner, Group, or Others columns to toggle Read, Write, or Execute.
- 2Or type an octal value directly (e.g. 755, 600, 644) to update the matrix automatically.
- 3Enter your target file or directory path in the command generator below.
- 4Toggle -R for recursive permissions on directories or -v for verbose output.
- 5Click "Copy Command" to paste the ready-to-run shell command directly into your terminal.
Frequently asked questions
How do the octal numbers (e.g. 755 or 644) work in chmod?
In Linux, permissions are represented in octal (base-8) by adding three binary values: Read (r = 4), Write (w = 2), and Execute (x = 1). The three digits correspond to Owner, Group, and Others. For example, 7 (4+2+1 = rwx) for Owner, 5 (4+1 = r-x) for Group, and 5 (4+1 = r-x) for Others equals 755.
Why should SSH private keys always be chmod 600 or 400?
OpenSSH enforces strict security requirements on private keys (e.g. ~/.ssh/id_rsa). If a key has permissions allowing Group or Others to read it (like 644), SSH will refuse connection with "WARNING: UNPROTECTED PRIVATE KEY FILE!". Setting chmod 600 ensures only you (Owner) can read/write the key.
Why is chmod 777 considered dangerous?
chmod 777 gives Read, Write, and Execute rights to every single user and process on the system. This allows unprivileged processes or compromised services (like web servers) to overwrite executable files, modify scripts, or inject malicious code. In production, standard files should be 644 and scripts/directories should be 755.
What are SUID, SGID, and Sticky Bit?
Special flags are prepended as a 4th octal digit: SUID (4) executes a program with the file owner's permissions (like /usr/bin/passwd). SGID (2) executes with group rights or inherits group ownership on directory creations. The Sticky Bit (1) on directories (like /tmp) prevents users from deleting or renaming files owned by other users.
The Senior Full-Stack Production Kit (2026)
Checklists, Docker recipes, and SSR error fixes in one dense PDF.