NAMEcow-shell - Start a copy-on-write session and invoke a shell.
DESCRIPTIONcow-shell Executes specified command with cowdancer or a shell if no command-line option is given.
Inside the cowdancer session, files under the current directory are protected in a way so that a write operation to an i-node which existed at the point of running cow-shell is not modified.
Useful for managing hard-linked source-trees and scratch-filesystems.
- cp -al cowdancer/ cowdancer.new && cd cowdancer.new && cow-shell
- Create a hardlinked tree, and cd into the newly created tree. After invoking cow-shell inside that tree, a write operation against a file that is hardlinked with the original tree will be copied to a new file before write.
- cp -al cowdancer/ cowdancer.new && cd cowdancer.new && cow-shell debuild
Tries to run dpkg-buildpackage on the new tree,
to avoid damage to the original tree.
Configure debuild to ignore .ilist files, through -i or -I option.
Generated dynamically in the current directory.
The file contains the list of i-node numbers that should be
protected from write operation.
The shared library used internally that overrides some functions
that potentially write to files.
This library implements the COW feature and is preloaded with
Used for copying.
Requires GNU option
to be functional.
The path to the current
Used internally to work around infinite loops.
It will be unset.
Utilized to preload
Enables debug messages.
cowdancer will give verbose debug messages in standard error output.
Specifies a different path for libcowdancer.so.
Enables reuse of cowdancer .ilist file found for consecutive runs of
The functions that are overridden with cowdancer will give an errno value of ENOMEM when there is a problem.
System isn't really out of memory, but this error code is chosen because this error is usually handled gracefully by applications.
Can only support directories that are scanned by cow-shell command.
The operation is not semantically correct when files are originally hardlinked, hardlinks are always broken.
Does not support anything when LD_PRELOAD trick does not work.
Does not work unless hardlinks are supported on the filesystem.
Not very user-friendly.
Leaves .ilist file around.
AUTHORJunichi Uekawa (email@example.com)
Upstream page is available at www.netfort.gr.jp/~dancer/software/cowdancer.html