1. chmod – change file or directory attributes. If you do “ls -l” in the present working directory, you would see file attributes for your files and directories in the present working directory. To change the permissions you can use “chmod”.
chmod XXX file_name
chmod XXX directory_name
Each ‘X’ denotes a value for “user”,”group” and “others” respectively. The ‘X’ above can be assigned value from 0-7. There are three types of permissions having a corresponding ‘X’ value as given below:
X=4: for read only.
X=2: for write only.
X=1: for execute only.
You can get a combination of permisssions eg. “read and write” by givng ‘X’ a combined value as ‘X=6’ (‘X=6’ is obtained by adding read and write value. Lets assume that you have a file “file.txt” and directory “test”, and you want to assign:
User – read, write and execute permission (X=4+2+1=7);
Group – read and write permissions (X=4+2=6); and
Others – read only permission (X=4).
To do that you can do the following:
chmod 764 file.txt
chmod 764 test
(Here we assume that the file “file.txt” and directory “test” are in present directory).
2. chgrp – To change group attribute of a file or directory. Each user belongs to a group. If you need to change the group the user belongs to use this command.
chgrp group_name file_name
chgrp group_name directory_name
For example, if you have file a file “file.txt” and directory “test”, and you want to assign a group “admin” to it, you can do that by:
chgrp admin file.txt
chgrp admin test