Linux: Changing file and dirctory permisions for an entire directory tree

Suppose you have a directory named /mydir and you need to change the permissions on all the files for the entire directory tree. Using a command like chmod -R 644 * might get you into trouble since this may change execute (i.e. traversal) access even for existing directories.

A friend from Germany (thanks Antoni) gave me the fhis solution :

First the files

find /mydir -type f -exec chmod 0644 {} \;

... and then the directories

find /mydir -type d -exec chmod 0755 {} \;

Note: The previous commands reset the file permissions completely. If you want to just add read access, while preserving the rest, you might prefer a u+r or g+r command line to chmod as in the following example which adds read and execute access to /mydir and all it's subdirectories.

find /mydir -type d -exec chmod u+rx {} \;

By the way, since I have lately found to need this more and more - as I move data to and from USB sticks -- I created a simple script that given a directory gives all files permissions 0644 and all directories 0755

#!/bin/bash
# File resetPerms.sh

if [ -d $1 ]
then
  echo Reseting file and directory access on $1
  find $1 -type f -exec chmod 0644 {} \;
  find $1 -type d -exec chmod 0755 {} \;
fi