17 October, 2020
Let’s look at how permissions work first. Linux permissions are implemented through the properties of files and are defined by three separate categories.
User: The person who owns the file.
Group: The 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.
|Read||r||4||View file contents.|
|Write||w||2||Write to me or change.|
|Execute||x||1||Run the file.|
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, the umask value is $002
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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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
+ --->To add a permission.
- --->To remove permission.
= --->To override the permission.
Here are some of the commands you can use to work with permissions:
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.
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
Chgrp: à By using this command we can change the group of the file.
Syn: Chgrp [options] [group name] [file]
R ---> Recursively
V ---> Verbose
Ex: #ls-l linux #chgrp sales linux
Chown: This command is used so we can change the owner of the file, as well as owner & group at a time.
Syn: Chown [options] [user:group] [file]
#Chown Raju Linux To Change the only owner.
#Chown Raju: sales Linux To Change owner & group
#Chown –R Ramu: color Unix Recursively to change.
To view the symbolic as well as a numeric mode of permission
# stat Linux
To change the permissions in GUI mode
Assign the permissions in GUI mode:
Right-click on file ----->properties---->permissions.