SysAd

1. SYSTEMS
ADMINISTRATION &
MAINTENANCE CLASS
Lesson 8 – File Permissions

2. Permissions on Files
Denoted by a letter
A permission represents an action that
can be done on the file
Occasionally referred as permission bits
Note that for script you need both
Execute and Read permission

3. Permissions on Directories
r, w and x has also meaning for directories
The meanings for directories is slightly different
Read r – permission to get a listing of the directory
Write w – permission to create, delete, or rename
files within the directory
Execute x – permission to change to the directory,
or to use the directory as an intermediate part of
the path of a file.

4. Examining Permissions
The ls –l command allows you to look at the
permissions of a file.

5. Preserving Permissions
By default the cp command makes no
attempt to preserve permissions
 -p to preserve permissions and timepstamp

6. How Permissions apply
If you own a file, the per-owner permission
apply to you
Otherwise if you are in the group that owns
the file, the per-group permissions apply to
you

7. Listing Directory Contents
ls Compact listing on non-hidden files
ls -a Compact listing of ALL files
ls -l Detailed listing of non-hidden files
ls -F Displays symbols to mark directories
and executable files
ls -ld Detailed listing of specified directory
ls -i Displays i-node number
(I.d. number of files)

8. Access Permissions
 Limiting unauthorized access to your directories and files
is a very important concern for ALL Linux (Unix) users.
 Consequences of Unauthorized Access:
 Copying your assignments (cheating)
 Using your account for illegal activity
 Using your account to send obscene messages
 Tampering with files

9. File / Directory Permissions
 The Linux (Unix) OS can allow the user to specify read,
write and execute permissions to the user, group or all
others (UGO) for files.
 A user can also specify read, write and execute
permissions for a directory. The execute permission for a
directory allows the person to view files in that directory

10. chmod Command
(Relative Method)
Used to change the access permissions of a file or directory
Format:
chmod [option] [who] [operation] [permission] file
chmod [option] [permission] file-list
 who relates to user (u) , group (g) or all others (o)
 operation relates to adding (+), removing (-) or
setting (=) permissions
 permissions are read (r), write (w) and execute (x)

11. chmod Command
(Relative Method)
Examples:
 Add Permission
chmod g+rw file.name
chmod o+x file.name
 Remove Permission
chmod g-w file.name
chmod a-w file.name (removes write for ugo)
 Set Permission
chmod o=rx file.name
chmod go=rx filename
Note: you can
use wildcard
symbols (eg *) to
match particular
files

12. File Access Rights
 Types of Users:
 Owner
 Group
 All/Other
 Types of Permissions:
 Read
 Write
 Execute
 Types of Files
 Directories
 Other files

13. Table 8.1 Summary of File Permissions in LINUX

14. Directory Permissions
 read = list files in the directory
 write = add new files to the directory
 execute = access files in the directory

15. Determining File Access Rights

16. Table 8.2 Permission Values

17. Table 8.3 Permissions for Access to courses, labs, and temp

18. Changing the Access Rights
Purpose – to set/change permissions in files
 chmod [options] octal-mode filelist
 chmod [options] symbolic-mode filelist
Options
 -R recursively process subdirectories

19. Table 8.4 Values for Symbolic Mode Components

20. Table 8.5 Examples of the chmod Commands and Their Purposes

21. Table 8.5 Examples of the chmod Commands and Their Purposes