Using the server flag -Cn

Please note that the use of -C1 is documented, however the use of other -Cn options are still undocumented, and are subject to change or removal without prior notice. Consider using the p4migrate utility instead to translate case. If you choose to use the -Cn flag, you must ALWAYS use this flag.  This is necessary both when starting your Perforce Server and when running checkpointing or upgrade operations.  If you do not do so, you risk corrupting your Perforce database and/or your checkpoint and journal.

What does the -Cn flag do?

When do I use it?

The -Cn flag instructs the Perforce Server to override the operating system's case handling behavior for the Perforce database. The flag was introduced in release 2004.2, and is a server side flag. From the release notes:

Forces the server to operate in case-sensitive (n=0) on Windows orcase-insensitive (n=1) mode on Unix. -C2 is an experimental 'hybrid'order: case folding but uniqueness preserving.

You use the -Cn flag when:

You want to change the way the Perforce Server handles the case, overriding the operating system's default case-handling.
You are migrating your Perforce Server to an operating system with a different case-handling method, but you wish to retain the existing method for case-handling.

You do NOT use the -Cn flag when:

You are not intending to override the operating system case-handling.

If you do not intend to override case-handling, you checkpoint the database, resolve any case conflicts and inconsistencies, then restore from this case-consistent checkpoint. This process is explained in more detail in Article #75: Cross-Platform Server Migration.

You MUST NOT use -C0 or -C2 when:

running your Perforce Server on a Windows platform, and one file name or path differs from another only in case. This will corrupt the corresponding archive files.

When using either -C0 or -C2, the Perforce Server makes a distinction between "//depot/file.txt" and "//depot/FILE.TXT", and tells the operating system to write "file.txt,v" or "FILE.TXT,v" accordingly. Although Windows is capable of preserving the case used, it is unaware of the difference between these two names. Therefore, "file.txt,v" overwrites or is appended to "FILE.TXT,v", and so too for the reverse, causing loss or corruption of revision content.

If you have not created a database, you can simply start the Perforce Server using the appropriate -Cn flag.

For an existing database, call or email Perforce Technical Support at support@perforce.com because this is not a trivial task. You will need to take a checkpoint of the database, then restore it including the appropriate -Cn flag in the "restore" command. This restore ensures that the order of the keys is appropriate for the case-handling. In addition, you will need to correct case differences using the p4migrate script, and change versioned file line endings.

Important: The -Cn flag can only be used against new Perforce databases. Using the -Cn flag against a Perforce Server that is already in use instantly renders the keys out of order. Not only does it make the data largely inaccessible, it could easily cause the btree code enough confusion to corrupt the tree.

Notes:

The 2007.2 release of the Perforce Server checks the case order of the database on startup. If there is a mismatch, an error is reported in the log:

Perforce server error:Database open error on db.counters!BTree Case Order Mismatch
As of 2010.1 -C1 is now documented in p4d -h $p4d -h$ -C1 Force server to be case insensitive

For a working example of using the -Cn flag see Article 516: Moving from Windows to Linux, Retaining Case-handling.

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