GNU arch

In computing, GNU arch is a revision control system, similar in purpose to tools such as CVS, SCCS, and Subversion. It is used to keep track of the changes made to a source tree and to help programmers combine and otherwise manipulate changes made by multiple people or at different times.

Contents

1 Features 2 Author 3 Criticism 4 Other versions 5 External links

Features

GNU arch uses a slightly different paradigm from most versioning systems, in that each revision is uniquely globally identifiable. This results in a very scalable system that allows easy merging and applying of changes from completely disparate sources.

GNU arch is decentralized, removing the need for a central server for which developers have to be authorized in order to contribute. Instead, GNU arch is designed so that a full read-only copy of a project is made accessible by a head developer via HTTP, FTP, or SFTP, and each contributor is encouraged to retrieve a copy of the project, make modifications, then publish their changeset to allow the head developer to manually merge said changeset into the official project that's later refreshed on the read-only copy.

To simulate the behavior of centralized revision control systems, the head developer could allow shell access (for example, SSH) to the server hosting the aforementioned read-only copy. Authorized users would have write access via the filesystem.

Some other features of GNU arch include:

• atomic commits: the commit is all-or-nothing—if it is interrupted before it is fully complete, the entire commit is rolled back to avoid corruption.
• changeset orientation: instead of tracking individual files, GNU arch tracks changesets (individual features or bugfixes), which may span multiple files.
• easy and sophisticated branching
• advanced merging
• cryptographic signatures to ensure integrity
• support for file and directory renaming
• tracking of symbolic links

Author

The primary author and maintainer of arch is Tom Lord, and for that reason it is sometimes referred to as tla, an acronym for Tom Lord's Arch. Lord started arch as a collection of shell scripts to provide an alternative to CVS. In 2003, arch became part of the GNU project.

Criticism

Perhaps the most common criticism of arch is that it is difficult to learn, even for users who have experience with other SCM systems. In particular, arch has a large number of commands, which can be intimidating for new users.

Some also criticize arch for using very unusual file naming conventions[1], which can create difficulties for using arch in scripts, some shells, and in porting arch to non-Unix operating systems. In addition to a perceived lack of portability, at present arch has a reputation of not scaling well to large trees.

Proponents of arch point out that the project is still maturing, and that any serious problems will likely be addressed as work continues.

Other versions

The ArX[2] and Bazaar[3] revision control systems originated as forks of arch.

External links

• The GNU Arch homepage
• The arch wiki
• An extensive tutorial on arch
• LWN.net article on arch