Page 193 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Unit 10: File System

2. w write notes
3. x execute

In the following examples, the chmod command is given together with the old and new modes
for the files concerned.
Here is a table of numbers that covers all the common settings. The ones beginning with “7” are
used with programs (since they enable execution) and the rest are for other kinds of files.
value meaning
777 (rwxrwxrwx): No restrictions on permissions. Anybody may do anything. Generally not a
desirable setting.
755 (rwxr-xr-x): The file’s owner may read, write, and execute the file. All others may read and
execute the file. This setting is common for programs that are used by all users.
700 (rwx------): The file’s owner may read, write, and execute the file. Nobody else has any rights.
This setting is useful for programs that only the owner may use and must be kept private from
others.
666 (rw-rw-rw-): All users may read and write the file.
644 (rw-r--r--): The owner may read and write a file, while all others may only read the file. A
common setting for data files that everybody may read but only the owner may change.
600 (rw-------): The owner may read and write a file. All others have no rights. A common setting
for data files that the owner wants to keep private.
The chmod command can also be used to control the access permissions for directories. In most
ways, the permissions scheme for directories works the same way as with files. However, the
execution permission is used in a different way. It provides control for access to file listing and
other things. Here are some useful settings for directories:

value meaning
777 (rwxrwxrwx): No restrictions on permissions. Anybody may list files, create new files in the
directory and delete files in the directory. Generally not a good setting.
755 (rwxr-xr-x): The directory owner has full access. All others may list the directory but cannot create
files nor delete them. This setting is common for directories that you wish to share with other
users.
700 (rwx------): The directory owner has full access. Nobody else has any rights. This setting is useful
for directories that only the owner may use and must be kept private from others.

Example:
Given a file ‘file1’ with the default access modes (read and write for the user), add read mode for
the group:
bash$ chmod g+r file1

user group others
Before: rw- --- ---
After: rw- r-- ---
Remove read and write access for everyone else from file ‘file2’ (showing that you can use
multiple permissions):
bash$ chmod o-rw file2
user group others
Before: rwx rw- rw-
After: rwx rw- ---

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