CS 279 - Week 5 Lecture 1 - 9-18-12

*   2 approaches to file limits...

    *   maximum size of a single FILE, 
        limited by a parameter named ULIMIT that's
        part of the kernel configuration

        ...some shells provide a 
	ulimit
	...command, to see this;

    *   OR, the superuser may impose a quota of the
        total file space (and/or even number of files)
        that a user's files can occupy

        (this CAN be different for different users)

*   set-uid bit
    *   when the set-uid bit of a program file is set,
        enables that program to run with the permissions
        of its OWNER rather than the with the permissions
	of the user running it;

    *   you'll see an s for the x in the OWNER's permissions
        if the set-uid bit IS set for a program;

        (and, as the owner, you can specify the set-uid bit
        with s when you use the chmod command)

    *   to see more: section 2.8.2, p. 48

*   set-gid -- like set-uid except it applies to
    group permissions rather than owner permissions

*   sticky bit --
    when set on a directory, prevents files in that
    directory from being deleted or renamed by anyone
    other than the owner

    when set on an executable program, it provides a
    means for retaining that program in memory when a
    program is to be shared among many users

*   umask!!

    *   a program creates a file, with some permissions;
        THEN, these permissions are REDUCED by the FILE
        CREATION MASK, also known as umask (user mask)

    *   umask 
        lets you see your file creation mask
        in octal (what gets SUBTRACTED from the initial
	permissions)

        umask -S
	lets you see your file creation mask
	in SYMBOLIC form, in terms of WHAT is "allowed through"