liunx chmod command

 

Linux / Unix chmod command

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About chmod
Syntax
Examples
Additional information
Related commands
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About chmod

Changes the permission of a file.

Syntax

chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...
chmod [OPTION]... --reference=RFILE FILE...

-c, --changes	like verbose but report only when a change is made
--no-preserve-root	do not treat `/' specially (the default)
--preserve-root	fail to operate recursively on `/'
-f, --silent, --quiet	suppress most error messages
-v, verbose	output a diagnostic for every file processed
--reference=RFILE	use RFILE's mode instead of MODE values
-R, --recursive	change files and directories recursively
--help	display this help and exit
--version	output version information and exit

Permissions
u - User who owns the file.
g - Group that owns the file.
o - Other.
a - All.
r - Read the file.
w - Write or edit the file.
x - Execute or run the file as a program.

Numeric Permissions:
CHMOD can also to attributed by using Numeric Permissions:

400 read by owner
040 read by group
004 read by anybody (other)
200 write by owner
020 write by group
002 write by anybody
100 execute by owner
010 execute by group
001 execute by anybody

Examples

The above numeric permissions can be added to set a certain permission, for example, a common HTML file on a Unix server to be only viewed over the Internet would be:

chmod 644 file.htm

This gives the file read/write by the owner and only read by everyone else (-rw-r--r--).

Files such as scripts that need to be executed need more permissions. Below is another example of a common permission given to scripts.

chmod 755 file.cgi

This would be the following 400+040+004+200+100+010+001 = 755 where you are giving all the rights except the capability for anyone to write to the file.cgi file(-rwxr-xr-x).

Finally, another common CHMOD permission is 666, as shown below, which is read and write by everyone.

chmod 666 file.txt

Additional information

Below is an example of how a file may be listed when typing ( ls -l ) at the prompt as well as information on how to interpret it.

-rw-rw-r-- 1   hope  123   Feb 03 15:36   file.txt

-	rw	rw-	r--	1	hope	123	Feb 03 15:36	file.txt
File	owner	group	everyone else	links	owner	size	mod date	file name