10 Jan 2009
Chmod is a command used to change file permissions. Given the right permissions, you can restrict or grant access to a file for specific groups or users. Here's the basic format:
"chmod 755 myfile.txt"
A file can have the following permissions corresponding to these numbers:
Read = 4
Write = 2
Execute = 1
In order to combine permissions, you just have to add the numbers together (ie, READ & WRITE permission is a 6). A file has to give these permissions to three groups of people. For example, each digit in the "755" of the chmod command above represents one of these groups:
Left-most Digit = Owner
Middle Digit = The file's group
Right-most Digit = All other users
so in the command above, we gave the owner read, write, and execute permissions; the group of the file got read and execute permissions; and all other users got execute permissions.
Hope that helps.
I build computer vision software at Flickr
. You can get updates on new essays by subscribing to my rss feed
. Occassionally, I will send out interesting links on twitter
so follow me if you like this kind stuff.