Chmod Calculator

See what permissions new files and directories will have with a given umask value.

Permission Types

Every file and directory has three sets of permissions for three classes of users:

• Owner (u): The user who owns the file
• Group (g): Users in the file's group
• Others (o): All other users

Each class can have three permission types:

Octal Notation

Permissions are represented as a 3 or 4-digit octal number. Each digit is the sum of its permission values (read=4, write=2, execute=1):

• 7 = rwx (4+2+1)
• 6 = rw- (4+2)
• 5 = r-x (4+1)
• 4 = r-- (4)
• 0 = --- (no permissions)

Special Permissions

• Setuid (4xxx): Run file as the owner. Shows as s in owner execute position
• Setgid (2xxx): Run file as group, or inherit group on new files in directory. Shows as s in group execute position
• Sticky bit (1xxx): Only owner can delete files in directory. Shows as t in others execute position

Umask

The umask is a mask that removes permissions from newly created files and directories. It is subtracted from the base permissions (666 for files, 777 for directories). A umask of 022 means new files get 644 and new directories get 755.

Common Permission Sets

• 755 (rwxr-xr-x) — Executable files, directories
• 644 (rw-r--r--) — Regular files, config files
• 700 (rwx------) — Private directories
• 600 (rw-------) — Private files (e.g., SSH keys)
• 777 (rwxrwxrwx) — Full access (generally avoid)
• 444 (r--r--r--) — Read-only for everyone
• 1777 (rwxrwxrwt) — Shared directories (/tmp)