Chmod Calculator
Visual Unix file permission calculator. Toggle checkboxes or enter a numeric value.
Common Presets
Read (4)
Write (2)
Execute (1)
Owner
Group
Other
000
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chmod 000 filename
Frequently Asked Questions
What does chmod 755 mean? +
chmod 755 gives the owner full permissions (read, write, execute = 7), while group and others get read and execute only (5). This is the standard permission for executable scripts and directories that others need to access.
What is the difference between numeric and symbolic chmod? +
Numeric (octal) mode uses three digits like 755 where each digit represents owner, group, and other permissions. Symbolic mode uses letters like rwxr-xr-x. Both represent the same permissions -- numeric is more compact, symbolic is more readable.
When should I use chmod 644 vs 755? +
Use 644 for regular files that don't need to be executed (like HTML, CSS, config files). Use 755 for executable files (scripts, binaries) and directories. The difference is whether the execute bit is set.
Why is chmod 777 considered dangerous? +
chmod 777 gives everyone (owner, group, and all other users) full read, write, and execute permissions. This means any user on the system can modify or delete the file, which is a significant security risk. Use more restrictive permissions whenever possible.
How do Unix file permissions work? +
Unix permissions have three categories (owner, group, other) and three permission types (read=4, write=2, execute=1). Each category's permissions are summed to get a digit 0-7. For example, read+execute = 4+1 = 5. The three digits together form the chmod value like 755.