Special files in a mount
A mount answers to a few names that no directory holds. mfsmount produces their content itself, so they are absent from ls. You read them by name.
| File | What a read returns | Where it answers | Who can read it |
|---|---|---|---|
.stats | What this mount has done since it started: the number of operations of each kind, and what its connection to the Master Server has cost. One counter per line. | The root of the mount. | Any user |
.params | The settings this mount works with: its options with the values in force, what the Master Server granted the session, and the versions of the mount, the Master Server and FUSE. One setting per line. | The root of the mount. | Only root |
.oplog | Every operation this mount performs from the moment you open the file. | The root of the mount. | Only root |
.ophistory | The same log. The read starts with up to 15 MiB of the operations that came before you opened it. | The root of the mount. | Only root |
.masterinfo | The connection of this mount, as binary data. The mfs* tools read this file to find the local proxy through which they reach the Master Server, so the file answers in every directory. Internal. | Every directory of the mount. | Any user |
.random | Pseudo-random bytes, as many as you read, without end. Internal. | The root of the mount. | Any user |
.mooseart | A moose, drawn in ASCII. | The root of the mount. | Any user |
You cannot create, rename or delete a file under one of these names in the root of a mount. In any other directory the names mean nothing, so a file may carry them.
Examples on this page use cat and its neighbors. On a system whose standard tools come from an implementation other than the GNU one, every file in this table except .masterinfo reads as empty through them, without an error. The mount's metafiles read as empty says what to run instead.
.stats and .params answer with a snapshot
Both .stats and .params answer with what was true when you opened them. Reading them twice takes two cat runs, not one long read.
In .stats, square brackets mark a value that describes the current state. Every other value is a counter that adds up.
Writing to .stats resets it: the counters that add up start from zero again. The values that describe the current state stay as they are.
The operations log does not end
A read of .oplog or .ophistory does not end: the mount keeps answering as it works, and sends a line holding a single # after a second with nothing to report. Stop the read yourself. Diagnostic tools covers what the lines say and what to do with them.
.masterinfo and .random are internal
Both are here because you may meet them, not because you can build on them. The content of both files belongs to the client. A later release may answer differently without saying so.
.random is a statistical generator, not a cryptographic one. The generator starts from the same state every time a mount starts. Two mounts started the same way answer with the same bytes. Do not use .random for keys, passwords or anything else that has to be unpredictable.
.mooseart also tells you that the mount answers
Reading .mooseart costs one command and needs neither the Master Server nor a chunk, so the read is the shortest check that a mount is alive. The eyes follow the clock, so a loop over the file animates it:
while true; do clear; cat /mnt/mfs/.mooseart; sleep 0.5; done