[Techtalk] Chmod explained ( was: "I need to use Windows because ...")

caitlynmaire at earthlink.net caitlynmaire at earthlink.net
Sun Aug 11 13:54:03 EST 2002

Hi, Suzi,

This is UNIX command line stuff which was incorporated into Linux,
> never encountered chmod at all, let alone know what chmod 755 means. 

chmod (at the command line) changes who can use the file.  There is a
matching command:  chown  That changes ownership of a file.  These
things can also be done graphically in Konqueror (and, I think,
Nautilus) if you want to eschew the command line.

The three digits (755) refer to the permissions assigned to owner (first
digit), group (second digit), and the rest of the world (third digit). 
Each digit is a digital (base 10) conversion of a three digit binary
number.  So, the seven in 755 is really 111 binary.  1=on 0=off.  The
first digit is the fours in binary, the second is twos, and the right
most is ones.  The fours correspond to read priveleges, the twos to
write, and the ones to execute.   

The 7 in 755 means that owner can read, write, or execute a file, since
7 equates to 111.  The first 5 means that the group can read or execute,
but not write, since 5 equates to 101.  The second 5 means that everyone
in the world can read or execute, but not write.

This is all 30+ year old UNIX stuff, hence it's somewhat arcane nature. 
If you want a reference that shows all the command line commands common
to all Linux distros, how they work, and what they mean, I
wholeheartedly recommend "Linux System Commands" by Patrick Volkerding
and Kevin Reichard.

> What is this, what does it do, am I changing something in my user 
> abilities, my directory, or the open office stuff?

You are changing the permissions of a single file, in this case the Open
Office binary.  A binary is the part of the program that you initially
run.  In Windows they are .exe files.

All the best,

More information about the Techtalk mailing list