Linux file permission

gistfile1.txt

Earlier we discussed about how to use octal permission bits with chmod. In this article, let us review how to use symbolic representation with chmod.

Following are the symbolic representation of three different roles:

u is for user,
g is for group,
and o is for others.
Following are the symbolic representation of three different permissions:

r is for read permission,
w is for write permission,
x is for execute permission.
Following are few examples on 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