File Permissions
- Just like every operating system, linux comes with a set of permissions that it uses to protect files, directories and devices on the system.
- These permissions can be manipulated to allow (or) disallow access to files and directories on different parts of the system.
Basic file permissions:
- Let’s look at how permissions work first. Linux permissions are implemented through the properties of files and defined by three separate categories.
User: person who owns the file.
Group: group that owns the file.
Other: All other users on the system.
- Permissions in linux can be assigned one of two ways. You can use the mnemonic or a single digit to represent the permission level.
| Operation | Digit | Mnemonic | Description |
| Read | r | 4 | View file contents. |
| Write | w | 2 | Write to or change. |
| Execute | x | 1 | Run the file. |
Default file permissions:
Umask: Universal mask is a default value that always gets dedicated from maximum file permission allocated for every file & directory.
- For super user umask value is # 022.
- For Normal user umask value is $002
For super user:
- Maximum permission of a file 666
-------------------------------Umask (-)022
- Default file permission ------> 644
- Maximum permission of a directory 777
---------------------------------Umask (-) 022
- Default directory permission 755
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For Normal user:
- Maximum permission of a file ------ 666
---------------------------------Umask (-)_ 002
-------------------------------------------------664
- Maximum permission of a directory --- 777
umask --- 002
(-)
775
- To see the umask # umask
- To change the umask # umask 222
- To view umask value from the fiel # vim /etc/ bashrc
Operators:
+ ---> To add a permission.
- ---> To remove a permission.
= ---> To override the permission.
- Here are some of the commands you can use to work with permissions:
(a) Chmod:- It is used to change the permission of a file and directory. It can be used by the owner of the file (or) by root.
Syn: Chmod [options] [permission] [file]
--R ---> Acts recursively.
--V ---> Provides verbose output.
EX: 1) # Chmod u+rw,g+r, o+x linux
# Chmod 641 linux
2) #chmod ugo =rw backup
(or)
# chmod 666 backup
3) #chmod U-W, g-r, o-x linux
4) #chmod -R U+W, g+r, o+x linux
5) #chmod -R 777 unix
6) # chmod 755 Unix
(b) Chgrp:
à By using this command we can change group of the file.
Syn: Chgrp [options] [group name] [file]
-R ---> Recursively
-V ---> Verbose
Ex: #ls -l linux
#chgrp sales linux
(c) Chown:- This command is used to we can change the owner of the file, as well as owner & group at a time.
Syn: Chown [options] [user:group] [file]
-R---> Recursively
-V---> Verbose.
EX: #Chown raju linux To Change only owner.
#Chown raju: sales linux To Change owner & group
#Chown –R ramu: color unix Recursivly to change.
- To view the symbolic as well as numeric mode of permission
# stat linux
- To change the permissions in GUI mode
#navtilus &
- Assign the permissions in GUI mode:
Right click on file -----> properties ----> permissions.
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