The CernVM-FS Fuse client comes with a built-in tracer that can be used to record file system accesses to repositories. The tracer produces a CSV file. Every file system call, such as opening a file or listing a directory, is written as another line into the log file.
In order to activate the tracer, set
CVMFS_TRACEFILE=/tmp/cvmfs-trace-@[email protected] # the cvmfs user must have write permission to the target directory
The @fqrn@ syntax ensures that the trace file is different for every
repository.
The trace is internally buffered. Therefore, it is important to either unmount
the CernVM-FS client or to call cvmfs_talk tracebuffer flush at the end
of a tracing session in order to produce a complete record.
By default, the trace buffer can keep 8192 recorded calls, and it will start to
flush on disk at 7000 recorded system calls. The buffer parameters can be
adjusted with the two parameters CVMFS_TRACEBUFFER and
CVMFS_TRACEBUFFER_THRESHOLD.
The generated trace log is a CSV file with the following fields
| Field | Description |
|---|---|
| Timestamp | Seconds since the UNIX epoch, miliseconds precision |
| Event code | Numerical ID for the system call. Negative numbers indicate internal events, such as mounting and unmounting. |
| Path | The repository relative target path of the system call |
| Event name | A string literal corresponding to the event code. |
The following events are known:
| Event ID | Description |
|---|---|
| 1 | Open file |
| 2 | List directory contents |
| 3 | Read symbolic link |
| 4 | Lookup path |
| 5 | Get file system metadata (e.g. df call) |
| 6 | Get file/directory metadata |
| 7 | List extended attributes of a file/directory |
| 8 | Read extended attributes of a file/directory |