Calculate Unix file permissions
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Calculate Unix file permissions with checkboxes. Convert between numeric and symbolic chmod notation. Free developer tool. This tool runs entirely in your browser — no data is sent to any server. It's fast, free, and works on any device.
Unix file permissions control who can read, write, and execute files — a fundamental security mechanism in Linux, macOS, and all Unix-like systems. Each file has three permission groups: Owner (the file creator), Group (users sharing a group), and Others (everyone else). Each group can have Read (4), Write (2), and Execute (1) permissions, combined as a single octal digit. So chmod 755 means: owner gets full access (7=4+2+1), group and others can read and execute but not write (5=4+1). Understanding chmod is essential for server administration, web hosting (setting correct permissions for PHP/Python files), securing sensitive data, and debugging 'permission denied' errors. Common values: 644 for files, 755 for directories and scripts.
It gives full read, write, and execute permissions to everyone — owner, group, and others. This is generally a security risk and should be avoided, especially on web servers where it could allow unauthorized file modification.
644 (rw-r--r--) means owner can read/write, others can only read — standard for regular files. 755 (rwxr-xr-x) adds execute permission — needed for directories (to enter them) and scripts (to run them).
Your user lacks the necessary permission for the operation. Check file ownership (ls -la) and permissions. You may need to use sudo, change ownership (chown), or adjust permissions (chmod).
The sticky bit (chmod +t, numeric 1xxx) on a directory means only the file owner can delete their files, even if others have write permission. Used on /tmp to prevent users from deleting each other's temporary files.
Numeric (chmod 755) sets all permissions at once — faster for known values. Symbolic (chmod u+x) modifies specific permissions — safer for targeted changes. Both achieve the same result; use whichever feels more natural.