contact :: legal :: webstats  also on this site: - select - home tech writings green business studies conspiracy popular pages welcome  also in this section:  tech index  most popular pages  search: Like this site? Your donation is welcome!

1. unix filesystem objects (files, directories, links, devices etc) have three types of access controls:
   1. file permissions (changed with chmod)
   2. user owner - the owner of the object (changed with chown)
   3. group owner - the group the object is a member of (changed with chgrp)

2. File permissions allow access to be controlled in terms of read (r), write (w), and execute (x).

3. Permission for read, write, and execute may be defined for the user-owner, for the group-owner, and for the world (any users who are not the owner of, or in the same group as, the object). Thus there are nine individual permissions (rwxrwxrwx) per object.

4. All users are members of at least one group, possibly more.

5. A new filesystem object inherits the user ownership of its creator, and the group ownership of its parent directory. Consequently, all objects have a user-owner, a group-owner, and a set of permissions.

6. The user-owner of an object can interact with that object based on the file permissions for the user-owner (eg. rwx------).

7. Any user who is a member of the same group as a particular filesystem object (ie. a group-owner) can interact with that object based on the file permissions for the group-owner (eg. ---rwx---).

8. Any user who is not the owner of, AND is not in the same group as, a particular filesystem object (ie. neither user-owner or group-owner) can interact with that object based on the file permissions for the world (eg. ------rwx).

9. File permissions (eg. rwxrwxrwx) may be represented numerically (eg. 777). These are equivalent and interchangable. The conversion is done by assigning a value to r (4), w (2) and x (1), then adding them together. This is done for the owner, for the group, and for the world, then these numbers are placed in a single string. Example:

   original permissions:

     rwxrw-r--
   

   English translation:

     OWNER: read, write, execute allowed
     GROUP: read, write allowed
     WORLD: read allowed
   

   conversion of English translation to numbers:

     OWNER: 4 + 2 + 1 = 7
     GROUP: 4 + 2 = 6
     WORLD: 4 = 4
   

   final numerical representation of original permissions:

     764
   

10. More:
    • https://en.wikipedia.org/wiki/Setuid
    • https://en.wikipedia.org/wiki/Sticky_bit
    • https://en.wikipedia.org/wiki/Chmod

related articles:  my FreeBSD diary  FreeBSD and ATA disks  adding a disk  upgrading a disk  FreeBSD backups  backing up to a remote volume  Samba as a file server (low security)  Samba as a file server (high security)  Samba as a Primary Domain Controller  Samba as a member server  Samba as a print server (with CUPS)  troubleshooting Samba  troubleshooting printing with CUPS  configuring sendmail  installing phpMyAdmin  dealing with mail for root  working with cron  installing and using GPG  automated PHP scripting  special-purpose users  upgrading to key-based authentication  distributed data warehousing  doing a minor version upgrade  upgrading from 6.1 to 6.4  upgrading 6.2 and below  installing and using Webmin  installing and using denyhosts  filesystem access controls  unix basics