cow-shell - Start a copy-on-write session and invoke a shell.
cow-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
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 LD_PRELOAD.
- Used for copying. Requires GNU option -a to be functional.
- The path to the current .ilist file.
- Used internally to work around infinite loops. It will be unset.
- Utilized to preload libcowdancer.so
- Debugging option. Enables debug messages. cowdancer will give verbose debug messages in standard error output.
- Debugging option. Specifies a different path for libcowdancer.so.
- Enables reuse of cowdancer .ilist file found for consecutive runs of cow-shell.
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.
Junichi Uekawa (email@example.com)
Upstream page is available at http://www.netfort.gr.jp/~dancer/software/cowdancer.html
|2006 Jan 25||cowdancer|