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File::DirSync - Syncronize two directories rapidly

$Id:,v 1.53 2007/08/20 14:34:44 rob Exp $


  use File::DirSync;

  my $dirsync = new File::DirSync {
    verbose => 1,
    nocache => 1,
    localmode => 1,



  #  and / or



File::DirSync will make two directories exactly the same. The goal is to perform this syncronization process as quickly as possible with as few stats and reads and writes as possible. It usually can perform the syncronization process within a few milliseconds - even for gigabytes or more of information.

Much like File::Copy::copy, one is designated as the source and the other as the destination, but this works for directories too. It will ensure the entire file structure within the descent of the destination matches that of the source. It will copy files, update time stamps, adjust symlinks, and remove files and directories as required to force consistency.

The algorithm used to keep the directory structures consistent is a dirsync cache stored within the source structure. This cache is stored within the timestamp information of the directory nodes. No additional checksum files or separate status configurations are required nor created. So it will not affect any files or symlinks within the source_directory nor its descent.


new( [ { properties... } ] )

Instantiate a new object to prepare for the rebuild and/or dirsync mirroring process.

  $dirsync = new File::DirSync;

Key/value pairs in a property hash may optionally be specified as well if desired as demonstrated in the SYNOPSIS above. The default property hash is as follows:

  $dirsync = new File::DirSync {
    verbose => 0,
    nocache => 0,
    localmode => 0,
    src => undef,
    dst => undef,

src( <source_directory> )

Specify the source_directory to be used as the default for the rebuild() method if none is specified. This also sets the default source_directory for the dirsync() method if none is specified.

dst( <destination_directory> )

Specify the destination_directory to be used as the default for the dirsync() method of none is specified.

rebuild( [ <source_directory> ] )

In order to run most efficiently, a source cache should be built prior to the dirsync process. That is what this method does. If no <source_directory> is specified, you must have already set the value through the src() method or by passing it as a value to the "src" property to the new() method. Unfortunately, write access to <source_directory> is required for this method.

  $dirsync->rebuild( $from );

This may take from a few seconds to a few minutes depending on the number of nodes within its directory descent. For best performance, it is recommended to execute this rebuild on the computer actually storing the files on its local drive. If it must be across NFS or other remote protocol, try to avoid rebuilding on a machine with much latency from the machine with the actual files, or it may take an unusually long time.

dirsync( [ <source_directory> [ , <destination_directory> ] ] )

Copy everything from <source_directory> to <destination_directory>. If no <source_directory> or <destination_directory> are specified, you must have already set the values through the src() or dst() methods or by passing it to the "src" or "dst" properties to new(). Files and directories within <destination_directory> that do not exist in <source_directory> will be removed. New nodes put within <source_directory> since the last dirsync() will be mirrored to <destination_directory> retaining permission modes and timestamps. Write access to <destination_directory> is required. Read-only access to <source_directory> is sufficient since it will not be modifed by this method.

  $dirsync->dirsync( $from, $to );

The rebuild() method should have been run on <source_directory> prior to using dirsync() for maximum efficiency. If not, then use the nocache() setting to force dirsync() to mirror the entire <source_directory> regardless of the dirsync source cache.

only( <source> [, <source> ...] )

If you are sure nothing has changed within source_directory except for <source>, you can specify a file or directory using this method.

  $dirsync->only( "$from/htdocs" );

However, the cache will still be built all the way up to the source_directory. This only() node must always be a subdirectory or a file within source_directory. This option only applies to the rebuild() method and is ignored for the dirsync() method. This method may be used multiple times to rebuild several nodes. It may also be passed a list of nodes. If this method is not called before rebuild() is, then the entire directory structure of source_directory and its descent will be rebuilt.

maxskew( [ future_seconds ] )

In order to avoid corrupting directory time stamps into the future, you can specify a maximum future_seconds that you will permit a node in the <source> directory to be modified.

  $dirsync->maxskew( 7200 );

If the maxskew method is not called, then no corrections to the files or directories will be made. If no argument is passed, then future_seconds is assumed to be 0, meaning "now" is considered to be the farthest into the future that a file should be allowed to be modified.

ignore( <node> )

Avoid recursing into directories named <node> within source_directory. It may be called multiple times to ignore several directory names.


This method applies to both the rebuild() process and the dirsync() process.

lockfile( <lockfile> )

If this option is used, <lockfile> will be used to ensure that only one dirsync process is running at a time. If another process is concurrently running, this process will immediately abort without doing anything. If <lockfile> does not exist, it will be created. This might be useful say for a cron that runs dirsync every minute, but just in case it takes longer than a minute to finish the dirsync process. It would be a waste of resources to have multiple simultaneous dirsync processes all attempting to dirsync the same files. The default is to always dirsync.

verbose( [ <0_or_1> ] )

  $dirsync->verbose( 1 );

Read verbose setting or turn verbose off or on. Default is off.

localmode( [ <0_or_1> ] )

Read or set local directory only mode to avoid recursing into the directory descent.

  $dirsync->localmode( 1 );

Default is to perform the action recursively by descending into all subdirectories of source_directory.

nocache( [ <0_or_1> ] )

When mirroring from source_directory to destination_directory, do not assume the rebuild() method has been run on the source already to rebuild the dirsync cache. All files will be mirrored.

  $dirsync->nocache( 1 );

If enabled, it will significantly degrade the performance of the mirroring process. The default is 0 - assume that rebuild() has already rebuilt the source cache.

gentle( [ <percent> [, <ops> ] ] )

Specify gentleness for all disk operations. This is useful for those servers with very busy disk drives and you need to slow down the sync process in order to allow other processes the io slices they demand. The <percent> is the realtime percentage of time you wish to be sleeping instead of doing anything on the hard drive, i.e., a low value (1) will spend most of the time working and a high value (99) will spend most of the time sleeping. The <ops> is the number of disk operations you wish to perform in between each sleep interval.

  $dirsync->gentle( 25, 1_000 );

If gentle is called without arguments, then some default "nice" values are set. If gentle is not called at all, then it will process all disk operations at full blast without sleeping at all.

proctitle( [ procname ] )

Enable proctitle mode which shows the current operation on the process title. If procname is specified, then it shows that string in the "ps" listing. Otherwise, the current $0 is used. This is mostly for progress tracking for convenience purposes.

  $dirsync->proctitle( "SYNCING" );

Default is not to alter the process title at all.

tracking( [ <0_or_1> ] )

Enable or disable tracking mode. Operation tracking is disabled by default in order to reduce CPU and memory consumption. See entries_* methods below for more details.


Returns an array of all directories and files updated in the last dirsync, an empty list if it hasn't been run yet.


Returns an array of all directories and files removed in the last dirsync, an empty list if it hasn't been run yet.


Returns an array of all directories and files that were skipped in the last dirsync, an empty list if it hasn't been run yet.


Returns an array of all directories and files that failed in the last dirsync, an empty list if it hasn't been run yet.


Support for efficient incremental changes to large log files using md5 checksum comparison on portions of or all of corresponding parts of both the larger source and smaller destination files. If no differences are found anywhere, including the very end of the destination file, then simply append the end of the source to the end of the destination until both files are identical again. Avoid making a full copy of the source and especially avoid writing the entire file since writes are so slow and plainful.

Support for hard linking the source files into the destination when they both reside on the same device instead of making a full copy.

Generalized file manipulation routines to allow for easier integration with third-party file management systems.

Support for FTP dirsync (both source and destination).

Support for Samba style sharing dirsync.

Support for VFS, HTTP/DAV, and other more standard remote third-party file management.

Support for dereferencing symlinks instead of creating matching symlinks in the destination.


If the source or destination directory permission settings do not provide write access, there may be problems trying to update nodes within that directory.

If a source file is modified after, but within the same second, that it is dirsynced to the destination and is exactly the same size, the new version may not be updated to the destination. The source will need to be modified again or at least the timestamp changed after the entire second has passed by. A quick touch should do the trick.

It does not update timestamps on symlinks, because I couldn't figure out how to do it without dinking with the system clock. :-/ If anyone knows a better way, just let the author know.

Only plain files, directories, and symlinks are supported at this time. Special files, (including mknod), pipe files, and socket files will be ignored.

If a destination node is modified, added, or removed, it is not guaranteed to revert to the source unless its corresponding node within the source tree is also modified. To ensure syncronization to a destination that may have been modifed, a rebuild() will also need to be performed on the destination tree as well as the source. This bug does not apply when using { nocache => 1} however.

Win32 PLATFORM: Removing or renaming a node from the source tree does NOT modify the timestamp of the directory containing that node for some reason (see test case t/110_behave.t). Thus, this change cannot be detected and stored in the source rebuild() cache. The workaround for renaming a file is to modify the contents of the new file in some way or make sure at least the modified timestamp gets updated. The workaround for removing a file, (which also works for renaming a file), is to manually update the timestamp of the directory where the node used to reside:

  perl -e "utime time,time,q{.}"

Then the rebuild() cache can detect and propagate the changes to the destination. The other workaround is to disable the rebuild() cache (nocache => 1) although the dirsync() process will generally take longer.


Rob Brown,


Copyright (C) 2002-2007, Rob Brown,

All rights reserved.

This may be copied, modified, and distributed under the same terms as Perl itself.


dirsync(1), File::Copy(3), perl(1)