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Using the standard Linux command rm to delete multiple files on a Lustre filesystem is not recommended. The rm command will generate a stat() operation on for each file it removes, meaning all of the attributes of a file (filetype, owner, permission, modification time, etc.) will be returned from the metadata server. A large number of stat() operations can place an increased load on the metadata server, resulting in lower performance and instabilities with the filesystem.

Instead, use munlink, a Lustre-specific command that will simply delete a file without performing a stat() operation. Below is an example of our recommended approach which consists of two steps.

The first step deletes all the files and soft links within a directory (and its subdirectories) with the use of munlink:

find -P ./processor0 -type f -print0 -o -type l -print0 | xargs -0 munlink

Here is an overview of each step in that command:

  • find 
    is a command that will search the indicated directory (and subdirectories within). The syntax defines a search for files and soft links.
  • -P
    restricts the search within the indicated directory tree and forces NO dereference of symbolic links. This warranties that the find command will not look for files within the links.
  • ./processor0
    is the directory from which the search will start
  • -type f -print0 -o -type l -print0
    This indicates that the find command will search for anything that is a file (-type f) or (-o) a soft link (-type l, this is the lower letter l).
  • -print0

    This indicates the format of the result of the "find" command. This particular format is able to catch strange file names, and ensures that they are readable for the next step (xargs). It needs to appear twice due to the "or" option (-o) explained in the previous bullet point.

  • The Pipe command ( represented by a single pipe line: |) makes the output of "find" to serve as input to the next command (xargs in this case).
  • xargs -0
    xargs will then convert the received list of files, line by line, into an argument for whatever command is specified at the end (in this case: munlink). The -0 flag is related to the format of the listed files; if you use -print0 in the find command you must use -0 in the xargs command.
  • munlink
    deletes each file and soft link in the list without overloading the metadata server

The second step is to remove the empty directories and subdirectories in the tree. Once all of the files and soft links were deleted, you can remove the empty directories with a similar command:

find ./processor0 -depth -type d -empty -delete

Again, the find command will search the directory processor0 and all subdirectories for any empty directories (-type d -empty) and delete them. The depth flag instructs find to process each directory's contents before the directory itself, then the most distant branches in the directory tree will be procesed first. The -delete action also implies -depth. To process a directory' contents before the directory itself. Please note that the flags passed to find are evaluated as an expression, so if you pass -delete first, find will attempt to delete below your starting directory.

We strongly recommend that all OpenFOAM users make use of munlink for deleting simulation output. Doing so will not only help keep a stable filesystem, but also provide a speedup over using the standard rm -rf command.