chmod

chmod changes the permissions of each given file according to mode, which can be either a symbolic representation of changes to make, or an octal number representing the bit pattern for the new permissions.

A combination of the letters ugoa controls which users' access to the file will be changed: the user who owns it (u), other users in the file's group (g), other users not in the file's group (o), or all users (a). If none of these are given, the effect is as if a were given, but bits that are set in the umask are not affected.

The operator + causes the selected file mode bits to be added to the existing file mode bits of each file; - causes them to be removed; and = causes them to be added and causes unmentioned bits to be removed except that a directory's unmentioned set user and group ID bits are not affected.

The letters rwxXst select file mode bits for the affected users: read (r), write (w), execute (or search for directories) (x), execute/search only if the file is a directory or already has execute permission for some user (X), set user or group ID on execution (+), restricted deletion flag or sticky bit (s). Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (u), the permissions granted to other users who are members of the file's group (g), and the permissions granted to users that are in neither of the two preceding categories (o).

A numeric mode is from one to four octal digits (0-7), derived by adding up the bits with values 4, 2, and 1. Omitted digits are assumed to be leading zeros. The first digit selects the set user ID (4) and set group ID (2) and restricted deletion or sticky (1) attributes. The second digit selects permissions for the user who owns the file: read (4), write (2), and execute (1); the third selects permissions for other users in the file's group, with the same values; and the fourth for other users not in the file's group, with the same values.

• GNU Coreutils Project Homepage [EN]

• GNU Coreutils [EN] @ Fedora Package
• GNU Coreutils [EN] @ Homebrew Formula

• chmod [EN] @ Wikipedia
• chmod [DE] @ Wikipedia

Documentation

• chmod [EN] @ GNU Coreutils Manual

• File permissions [EN] @ GNU Coreutils Manual
  • Structure of File Mode Bits
  • Symbolic Modes
  • Numeric Modes
  • Operator Numeric Modes
  • Directories and the Set-User-ID and Set-Group-ID Bits

• man 1 'chmod' [EN]

Syntax

chmod [PARAMETER ...] MODE FILE [...]

Parameters

-c, --changes

Like verbose but report only when a change is made.

-R, --recursive

Change files and directories recursively.

-v, --verbose

Output a diagnostic for every file processed.

Examples

Change all permissions in the user's home directory

find "${HOME}" '(' -type 'd' -execdir chmod --changes 0700 '{}' '+' ')' \
           -or '(' -type 'f' -execdir chmod --changes 0600 '{}' '+' ')'