Tips from an RHCE: New default mount options in Red Hat Enterprise Linux 5

Contributed by Forrest Taylor

Newly created file systems in Red Hat Enterprise Linux 5 now have new default mount options. For instance, if I created /boot at install time on /dev/sda1, I can view these new mount options using tune2fs:

# tune2fs -l /dev/sda1
tune2fs 1.39 (29-May-2006)
Filesystem volume name:   /boot
Last mounted on:          <not available>
Filesystem UUID:          ea84e45d-ba84-4346-bf7c-1988c123a4a5
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index
filetype needs_recovery sparse_super large_file
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
...

We are interested in this line:

Default mount options:    user_xattr acl

These options apply for the file system at mount time. Thus, these newly created file systems will be able to use access control lists (ACL) and user extended attributes with no additional options.

ACLs are used to give multiple users and groups permissions to files and directories. This extends the standard Linux permissions of having one user permission, one group permission, and a permission for all others.

user_xattr is an option to store the user extended attributes. This allows added attributes to be stored with the file, including mime-types, descriptions, etc. Some programs, such as Beagle, use these extended attributes for storing data with the files.

One caveat here: the installer runs the tune2fs command on newly created file systems, giving it the acl and user_xattr options. File systems that were created before or after the installation will _not_ have these options by default. You can run tune2fs manually just like the installer did. Here is the exact command that anaconda runs, assuming that the partition is /dev/sda1:

tune2fs -c 0 -i 0 -O dir_index -o user_xattr,acl /dev/sda1

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This entry was posted by the editorial team on Thursday, June 7th, 2007 at 10:10 am and is filed under tips and tricks. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.