Under Unix, the only users authorized to change permissions on a file, are root and the file owner...
If you're the owner of the file, you can change the first position to a 2, 6 or 7...
Examples:
chmod 200 <filename>
chmod 600 <filename>
chmod 700 <filename>
These first 3 examples give write permission to the owner of the file. The first example give write only, but not read... The second example gives read and write permission only... The third example gives read, write and execute permissions to the owner...
The second position in the above trinome indicates the permissions that you as the owner, are granting to all users belonging to the same group that you belong to...
The third position in the above trinome indicates the permissions that you as the owner, are granting to everyone in the world...
0 - No permission
1 - Execute only
2 - Write only
3 - Write and Execute only
4 - Read only
5 - Read and Execute only
6 - Read and Write only
7 - Read, Write and Execute
Normally, only 3 numbers are given...
If 4 numbers are given, the first number is called a "sticky bit"...
If the file is executable, the sticky bit indicates whether the file is executed as the owner, a group member, or someone else, not part of the group...
This has significant meaning, if a stranger is allowed access to your programs...
