This is the other method of giving file permission using bits.
we are having 3 different roles of symbolic representation.The representation given below:
- user,
- group,
- others.
And the file/directory permissions are :
- read permission,
- write permission,
- execute permission.
Numeric values for the read, write and execute permissions:
- read 4
- write 2
- execute 1
Octal representation for permissions:
- First number is for user
- Second number is for group
- Third number is for others
$ chmod 765 filename
In this example 7 is for user , 6 for group and 5 for others.
For example, give read, write ( 4+2 = 6 ) to user and read ( 4 ) to group and others.
$ chmod 644 filename
The table will help us to understand more about giving permissions.
4 2 1
Read Write Execute
0 – – –
1 – – 1
2 – 1 –
3 – 1 1
4 1 – –
5 1 – 1
6 1 1 –
7 1 1 1
Umask
The umask acts as a set of permissions that applications cannot set on files. It’s a file mode creation mask for processes and cannot be set for directories itself. Most applications would not create files with execute permissions set, so they would have a default of 666, which is then modified by the umask.
Default file permission: 666
Default directory permission: 777
So if our umask value is 022, then any new files will, by default, have the permissions 644 (666 – 022). Likewise, any new directories will, by default, be created with the permissions 755 (777 – 022).
You can change the umask value to appropriate value of what you need based upon the above calculation. For example,
$ umask 077
