chmod linux command

chmod

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 its 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 may be specified, 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 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; save text (file) mode or prevent removal of files by nonowners (directory).

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:

Read.

Write.

Execute.

Note: A fourth digit may precede this sequence. This digit assigns the following modes:

Set user ID on execution to grant permissions to process based on file's owner, not on permissions of user who created the process.

Set group ID on execution to grant permissions to process based on the file's group, not on permissions of user who created the process.

Set sticky bit.

Examples

Add execute-by-user permission to file:

Either of the following will assign read/write/execute permission by owner (7), read/execute permission by group (5), and execute-only permission by others (1) to file:

Any one of the following will assign read-only permission to file for everyone:

Set the user ID, assign read/write/execute permission by owner, and assign read/execute permission by group and others: