gnulinuxclub

We have already discussed the directory structure in
Linux/Unix. You
are able to find files and directories that you need. But there is more
to the filesystem than just the directory structure.

Linux/Unix is a multiuser operating system. Every aspect
of
the system is
multiuser, even the filesystem. The system stores information like who
owns a file and who can read it. There are other unique parts about the
filesystems, such as links and NFS mounts. This section explains these,
as well as the multiuser aspects of the filesystem.

In Linux/Unix, all files are protected under some access
control mechanism, so
that the owner of a file can deny access of his files to other
users. The first column of the long directory list shows the access
characteristics of a file, in te form of 10 flags, e.g. drwxr-xr-x.

drwxr-xr-x? 18 gaurav
gaurav??? 784 2005-04-14 08:31 .

The meanings of the flags are shown below:

Position 1       file type: d (directory) 
                            - (ordinary file)
                            l (symbolic link)

Position 2-4     permissions for the owner: r (read)
                                            w (write)
                                            x (execute)

Position 5-7     permissions for other users in the same group

Position 8-10    permissions for all other users

Note that a hyphen (`-‘) denotes lack of the given permission type.
For example, r-x would mean that read and execute permission are
granted, but not write permission.

In order to remove a file, you must have write
permission for
it.

In order to view the contents of a directory, i.e. see
what
files
are there, you need read permission for that directory. In order
to actually access a file (read from it, write to it, or execute
it) in the directory, you need execute permission for the directory.

   -rwxr-xr-x   1 root     bin    7368 Jul 30  1999 /usr/bin/wc
   

# chown daemon /usr/bin/wc

# chgrp root /usr/bin/wc

# chown daemon.root /usr/bin/wc

References:

http://slackware.com

http://heather.cs.ucdavis.edu/~matloff/UnixAndC/Unix/FileSyst.html

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