Slide 1 : Managing User Account and Privileges
Slide 2 : User and Groups Every User of the system is assigned a unique User ID number ( the uid).
Users name and uid are stored in /etc/passwd.
User are assigned to groups with unique group ID number ( the gid).
gid are stored in /etc/group.
Slide 3 : Permissions are set for :
The owner of the file (called the “user”)
The group member’s
All others
Permissions that are set are called read, write and execute permissions. Linux File Security
Slide 4 : Examining permissions $ ls –l /bin/login
-rwxr-xr-x 1 root root 19080 Arp 1 18:26
/bin/login.
Slide 5 : TEXT TEXT TEXT User Categories File permissions are established for each of three user categories. Each category also has a one-letter symbol :
u -- the file’s owner (user)
r -- other users in the file group
o -- everyone else (others)
Slide 6 : File Permission Types Four symbols are used when displaying permissions:
r : permission to read a file or list a directory’s
content.
w : permission to write to a file or create add
remove files from a directory.
x : permissions to execute a program or change
into a directory and do a long listing of the
directory
- : no permission ( in place of the r,w or x)
Slide 7 : Default file Permissions Read and write for all is the default.
umask can be used to withhold permission upon file creation.
Non-privileged users umask is 0002 -- Files will have permission 0f 664.
Root’s umask is 0002
Slide 8 : Uses a three- digits mode number
First digit specifies owner’s permissions
Second digits specifies group permissions
Third digit represent other’s permission
Permissions are calculated by adding
4 (for read)
2 (for write)
(for execute)
Example:
chmod 640 myfile Changing Permissions - Numeric Method
Slide 9 : To start a new shell as a different user:
su
su username Changing your identity
Slide 10 :