Linux in a Nutshell, Fourth Edition

Name

chmod

Synopsis

                  chmod [options] mode 
                  files
                  chmod [options] --reference=
                  filename 
                  files
               

Change the access mode (permissions) of one or more files. Only the owner of a file or a privileged user may change the mode. mode can be numeric or an expression in the form of who opcode permission. who is optional (if omitted, default is a); choose only one opcode. Multiple modes are separated by commas.

Options

-c, --changes

Print information about files that are changed.

-f, --silent, --quiet

Do not notify user of files that chmod cannot change.

--help

Print help message and then exit.

-R, --recursive

Traverse subdirectories recursively, applying changes.

--reference= filename

Change permissions to match those associated with filename.

-v, --verbose

Print information about each file, whether changed or not.

--version

Print version information and then exit.

Who

u

User.

g

Group.

o

Other.

a

All (default).

Opcode

+

Add permission.

-

Remove permission.

=

Assign permission (and remove permission of the unspecified fields).

Permissions

r

Read.

w

Write.

x

Execute.

s

Set user (or group) ID.

t

Sticky bit; used on directories to prevent removal of files by non-owners.

u

User’s present permission.

g

Group’s present permission.

o

Other’s present permission.

Alternatively, specify permissions by a three-digit octal number. The first digit designates owner permission; the second, group permission; and the third, other’s permission. Permissions are calculated by adding the following octal values:

4

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