Following are few examples of Some Linux file access permission commands and how to use the symbolic representation on chmod.
1. Add single permission to a file/directory
Changing permission to a single set. + symbol means adding permission. For example, do the following to give execute permission for the user irrespective of anything else:
$ chmod u+x filename
2. Add multiple permission to a file/directory
Use comma to separate the multiple permission sets as shown below.
chmod u+r,g+x filename
3. Remove permission from a file/directory
Following example removes read and write permission for the user.
$ chmod u-rx filename
4. Change permission for all roles on a file/directory
Following example assigns execute privilege to user, group and others (basically anybody can execute this file).
$ chmod a+x filename
5. Make permission for a file same as another file (using reference)
If you want to change a file permission same as another file, use the reference option as shown below. In this example, file2′s permission will be set exactly same as file1′s permission.
$ chmod --reference=file1 file2
6. Apply the permission to all the files under a directory recursively
Use option -R to change the permission recursively as shown below.
$ chmod -R 755 directory-name/
7. Change execute permission only on the directories (files are not affected)
On a particular directory if you have multiple sub-directories and files, the following command will assign execute permission only to all the sub-directories in the current directory (not the files in the current directory).
$ chmod u+X *
Note: If the files has execute permission already for either the group or others, the above command will assign the execute permission to the user