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Permissions are used to control who can access your files and
directories. When you create a new file it is important to consider
who should be able to view this file.
The UNIX file system has three different permissions associated
with each file and directory. Read permission lets a person
look at and copy a file or directory. Write permission
lets a person edit, change, and delete a file or directory.
Execute permission lets a person run a file which is a program
or software package. Execute permission on a directory lets a person
make that directory their current working directory. Because there
are many people sharing one file system, permissions on files need
to be set for different types of people. For example, if Joe is
working on his thesis, he will want to read and write to the file
called chapter1.tex in his thesis directory. He may also
want to let his advisor read chapter1.tex. He may not want everyone
else with an account to read chapter1.tex though. Permissions are
set on three different levels. There are permissions for the
user of the file (commonly referred to as the owner
of the file), for the group of people working with the
user, and for the others which are people who have accounts
on this machine but aren't a part of the group. In Joe's example,
he would be the user of the file, he would have a
group for himself and his advisor, and everyone using the machine
are considered the others. The system administrator sets
up the groups and they are usually very general (for example all
faculty members are in one group). If you would like to have a group
of people created to work on a specific project, ask the system
administrator to set this up for you.
Next: Changing Permissions
on Up: Introduction
to UNIX Previous:
Information about Files
Tim Kohl
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