Linux Permission

 

 

	File	Directory
Read (4)	Read	List
Write (2)	Write ,modify	Create, Delete
Execute (1)	Run (Can also read it)	cd (Can also read it)

 

 

1) change the file owner  

To change the file or directory owner :  chown <user>:<group> <file or directory>   // <group is optional>

To change the file or directory  groups: chgrp <group> <file or directory>  

 

2) change file permission

chmod xyz <filename> 

 x : owener permisson , it is the sum value of Read , write and Execute (4,2,1)

y: group permission

z: others permission 

special chmod +t <directory>

+t is "sticky bit", it means the files in directory and subdirectory cannot be delted by other user unless the owner ; to clear it use chmod -t 

bsc@ubuntu:/home/test$ sudo chmod +t account/
bsc@ubuntu:/home/test$ ls -lt
total 52
drwxrwx--T+ 2 root account 4096 Apr 19 13:22 account

 

3)  File Permission example :  

-rwxrwxrwx 1 bsc yu 11 Apr 19 05:42 test     , the first - indicate it is file or directory,  following rwx indictes the permission of read. write, and excute for owner, following rwx indicates the permissions of group, and last rwx indicate the permission for others.

t  /user who is the owner can delte the file

 

4)  File access control list

e.g if we want give rw permission to the account group for the dir named linda which belongs to sales group and owner linda

drwxr-xr-x 2 linda sales 4096 Apr 19 06:42 linda

bsc@ubuntu:/home$ sudo setfacl -R -m d:g:account:rx linda/    // -R apply the change to sub-directory, -m for change g:account:rx  apply the rx permission to account user group. d flag will apply the permission to future new create file
bsc@ubuntu:/home$ ls -lt
drwxr-xr-x+ 2 linda sales 4096 Apr 19 06:42 linda ,  // + shows it has ACL applied

getacl  <file name>  // to check the acl of this file

 

5) attribute of file 

e.g use chattr +i <file name> so that the file  will be not changeable 

use  lsattr <file name> to check the file attribute

to change the file back, use  chattr -i <file name> 

 

6) Find file with spefici permission

find  <path to search> -perm  <+ or - or / or empty><permison numebr e.g 777>

e.g 

bsc@ubuntu:/home/linda$ find ./ -perm 770 -exec ls -lt \;

-rwxrwx---+ 1 linda sales 11 Apr 19 07:00 test.txt

• without any + - or / indicate search the mode exactly 770 for user any 

• find . -perm /220
  find . -perm /u+w,g+w
  find . -perm /u=w,g=w

  All three of these commands do the same thing, but the first one uses
  the octal representation of the file mode, and the other two use the
  symbolic form. These commands all search for files which are writable
  by either their owner or their group. The files don't have to be
  writable by both the owner and group to be matched; either will do