Commands to set the access permissions for files and directories

IRIX provides us a method to define the access privileges for users other than the owner of the file or directory. Normally, owner of the file or directory is the user who actually creates a file or directory by logging into his own account.

Let us assume that the user account matnajx has created a C source file example.c, on hydra. Following operations can be performed on this file:

1. A file can be modified by changing its contents. This operation is known as write operation. (Deletion is a special write operation in which all the contents of the file are destroyed.)

2. A file can simply be read without changing any contents. This is known as the read operation.

3. A file can be executed (if it is indeed an executable file).

The access previleges for a file can be set by the command chmod access_bits file_name Where access_bits can be the octal digits LMN (L, M, N can be from 0 to 7)

L: specifies Access privileges for the owner

M: specifies Access previleges for the users of the same group as the owner

N: specifies Access previleges for all the other users

Every digit L, M or N can specify following types of permissions:

0: Neither read nor write nor execute

1: Only execute

2: Only write

3: Only write and execute

4: Only read

5: Only read and execute

6: Only read and write

7: All the three privileges

For example, the command chmod 775 example.c sets the following privileges for example.c.

• Read,write and execute by the owner.
• Read,write and execute by the users of the same group.
• Read,write by all the other users.