File System Architecture , Links, Special File Permission , Access Control Lists (Lec 20,21,23,24)

in this file system there are 498784 inodes and so on.'

tune2fs == allows the system adminstrator to adjust various tunable filesystem parameters on linux ext2, ext3, ext4 filesystems.

 

i only typed less /etc/passwd but when you check out with lsof command with pid there are many files opened , because of dependency.

0u , 1u, 2u is the file descriptor stdin, stdout, stderr , and we have our less command at 4r

 

Hard Link , Soft Link

unlike hard link if you remove actual file , soft link will be dangling pointer.

 

Special File Permission (SUID, SGID, STICKY)

SUID

if you use $ chmod u+S file  your are giving S bit permission to that file which is executable. it will execute with the power of the owner of that file 

if it is so harmful why OS has given this facility of Suid bit? 

$ find / -perm /4000 >2 /dev/null 

this will tell you who has the suid bit file. ex) /bin/su , /bin/mount , /usr/bin/passwd , /usr/bin/sudo

/usr/bin/passwd is used for changing password inside /etc/shadow. 

but /etc/shadow has no permission for other users. but you cannot change other user's password because of passwd checks UID internally even though you have suid bit on.

SGID

$ find / -perm /4000 >2 /dev/null looks for files that have SGID bit 

/usr/bin/chage  runs power of group which is shadow  and also /etc/shadow has group shadow.

for directory if you set SGID bit. and make file there, file will have group permission as other group not self , for example student. 

STICKY

$ chmod o+t  by using this command you set sticky bit on directory

and only the owner of certain file can delete certain file

$ find / -perm /1000 2>/dev/null   

 

Access Control Model

1. DAC(Discretionary Access Control) == holds the business owner resposnible for deciding which people are allowed in a specific location, pyhsically or digitally

2. MAC(Managed Access Control) == require an elevated emphasis on the confidentiality and classification of data.

3. RBAC(Role-Based Access Control) == used when system administrators need to assign right based on organizational roles instead of individual user accounts within an organization.

Files System  ACL(Acess Control List)s

mask is union of all the permission of the file. 

with extended attribute you can make file only available for appending.