fatrace - Man Page

report system wide file access events

Examples (TL;DR)

Print file access events in all mounted filesystems to stdout: sudo fatrace
Print file access events on the mount of the current directory, with timestamps, to stdout: sudo fatrace [-c|--current-mount] [-t|--timestamp]

Description

fatrace reports file access events from all running processes.

It does not report file access by fatrace itself, to avoid logging events caused by writing the output into a file. It also ignores events on virtual and kernel file systems such as sysfs, proc, and devtmpfs.

Its main purpose is to find processes which keep waking up the disk unnecessarily and thus prevent some power saving.

By default, events are reported to stdout. This will cause some loops if you run this tool in e. g. gnome-terminal, as this causes a disk access for every output line. To avoid this, redirect the output into a file.

Output Format

There are two output formats. The default text format is easier on human eyes, while the JSONL format is more suitable for automatic processing.

In text format, a typical event looks like

rsyslogd(875): W /var/log/auth.log
compiz(1971): O device 8:2 inode 658203

In text format, the line has the following fields:

The current time, if you specify the --timestamp option.
Process name. This is read from /proc/pid/comm, which might be abbreviated for long process names.
Process ID
UID and GID, if you specify the --user option. It is formatted as "[uid:gid]".
Event type: Open, Read, Write, Close. Events on directories are + (create), Delete, < (moved from), or > (moved to). Combinations are possible, such as CW for closing a written file, or <> for renaming a file within the same directory.
Directory events can only be detected on Linux 5.1 or higher.
Affected file. In some cases the path and name cannot be determined, e. g. because it is a temporary file which is already deleted. In that case, it prints the devices' major and minor number and the inode number. To examine such a process in more detail, you should consider using strace(1).
Path to executable, if you specify the --exe option. This is read from /proc/pid/exe.
Parent process information, if you specify the --parents option. This information includes, for each successive parent process, the process ID, the process name, and the executable path if you specify the --exe option. If fatrace fails to determine some of this information, fields may be missing or the list may end before the process with ID 1.

In JSONL format, the line is a JSON-encoded object with the following fields:

timestamp

The current time, if you specify the --timestamp option.

comm

Process name. This is read from /proc/pid/comm, which might be abbreviated for long process names.

comm_raw

The raw bytes of the process name, in case it is invalid UTF-8 or would require escaping.

pid

Process ID

uid

UID, if you specify the --user option.

gid

GID, if you specify the --user option.

types

Event type: Open, Read, Write, Close. Events on directories are + (create), Delete, < (moved from), or > (moved to). Combinations are possible, such as CW for closing a written file, or <> for renaming a file within the same directory.

Directory events can only be detected on Linux 5.1 or higher.

device

device ID in {"major":major,"minor":minor} form.

inode

The file inode.

path

The path to the affected file.

path_raw

The raw bytes of the path to the affected file, in case it is invalid UTF-8 or would require escaping.

exe

The path to the executable, if you specify the --exe option.

exe_raw

The raw bytes of the executable path, in case it is not valid UTF-8 or would require escaping.

parents

An array of parent processes, if you specify the --parents option. Each item is an object containing pid, comm, comm_raw, exe and exe_raw fields as appropriate. If fatrace fails to determine some of this information, fields may be missing or the list may end before the process with ID 1.

Options

-c, --current-mount

Only record events on partition/mount of current directory. Without this option, all (real) partitions/mount points are being watched.

-o FILE, --output=FILE

Write events to given file instead of standard output.

-s SECONDS, --seconds=SECONDS

Stop after the given number of seconds.

-t, --timestamp

Add timestamp to events. When this option is given once, the format will be a human readable hour:minute:second.microsecond; when given twice, the timestamp is printed as seconds/microseconds since the epoch.

-u, --user

Add process user information to events.

-p PID, --ignore-pid=PID

Ignore events for this process ID. Can be specified multiple times.

-f TYPES, --filter=TYPES

Show only the given event types. TYPES is a list of C, R, O, W, D, +, or < with the above meanings. < and > both mean "move" and will always enable both directions.

E. g. use --filter=OC to only show open and close events.

-C COMMAND, --command=COMMAND