fs_bypassthreshold - get/set Cache Bypass file size threshold


fs bypassthreshold [-size <file size>] [-help]

fs bypassthresh [-s <file size>] [-h]


The fs bypassthreshold command either changes the AFS client Cache Bypass file size threshold, or reports the current threshold. Normally, when an application tries to read data via the OpenAFS client, the client will fetch the required data from the fileserver, store the results in the local cache, and then serve the application request from the local cache. When the Cache Bypass feature is enabled, certain files will be read directly from the network, and the data will not be saved to the local cache. In some scenarios, this can provide a significant performance improvement, especially if the data is only read once.

Currently, the only way to specify which files should bypass the cache and which files should not, is by file size. In the future, different mechanisms may exist for specifying which files should bypass the local cache and which should not.

If -size is not specified, fs bypassthreshold just reports the current threshold and exits.


Cache Bypass is still considered an experimental feature. Even in stable releases of OpenAFS, it is not considered as stable as the rest of OpenAFS.


-size <file size>

Specifies how large a file must be in order to enable Cache Bypass mode. If a file is larger than the specified file size (in bytes), reading from that file will bypass the local cache and be read directly from the network. A file size of -1 indicates that Cache Bypass should be disabled complete, so no files will enable Cache Bypass mode, no matter how large they are.

By default, Cache Bypass is disabled.


Prints the online help for this command. All other valid options are ignored.


The output format is identical whether or not -size was specified. If -size is specified, the bypass threshold is changed, and the output represents the new, changed, threshold. Otherwise the output represents the current threshold.


The following example turns on Cache Bypass with a threshold of 4KiB:

   % fs bypassthreshold 4096
   Cache bypass threshold 4096

The following example disables Cache Bypass:

   % fs bypassthreshold -1
   Cache bypass threshold -1 (disabled)

The following example examines the current Cache Bypass threshold:

   % fs bypassthreshold
   Cache bypass threshold 4096


To set the bypass threshold, the issuer must be logged in as the local superuser root. Otherwise, no privilege is required.


Copyright 2012 Sine Nomine Associates

This documentation is covered by the BSD License as written in the doc/LICENSE file. This man page was written by Andrew Deason for OpenAFS.