Wednesday, June 9, 2010

Chmod Command

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 filename2. Add multiple permission to a file/directory
Use comma to separate the multiple permission sets as shown below.

$ chmod u+r,g+x filename3. Remove permission from a file/directory
Following example removes read and write permission for the user.

$ chmod u-rx filename4. 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 filename5. 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 file26. 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 *
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