FS_USAGE(1) General Commands Manual FS_USAGE(1)
fs_usage – report system calls and page faults related to filesystem
activity in real-time
fs_usage [-e] [-w] [-f mode] [-b] [-t seconds]
[-R rawfile [-S start_time -E end_time]]
[pid | cmd [pid | cmd [...]]]
The fs_usage utility presents an ongoing display of system call usage
information pertaining to filesystem activity. It requires root privileges
due to the kernel tracing facility it uses to operate. By default, the
activity monitored includes all system processes except the running
fs_usage process, Terminal, telnetd, telnet, sshd, rlogind, tcsh, csh, sh,
and zsh. These defaults can be overridden such that output is limited to
include or exclude a list of processes specified by the user.
The output presented by fs_usage is formatted according to the size of your
window. A narrow window will display fewer columns of data. Use a wide
window for maximum data display. You may override the window formatting
restrictions by forcing a wide display with the -w option. In this case,
the data displayed will wrap when the window is not wide enough.
The options are as follows:
-e Specifying the -e option generates output that excludes sampling of
the running fs_usage tool. If a list of process IDs or commands is
also given, then those processes are also excluded from the sampled
-w Specifying the -w option forces a wider, more detailed output,
regardless of the window size.
-f Specifying the -f option turns on output filtering based on the
mode provided. Multiple filtering options can be specified. By
default, no output filtering occurs. The supported modes are:
network Network-related events are displayed.
filesys Filesystem-related events are displayed.
pathname Pathname-related events are displayed.
exec Exec and spawn events are displayed.
diskio Disk I/O events are displayed.
cachehit In addition, show cache hits.
-b Specifying the -b option annotates disk I/O events with BootCache
info (if available).
Specifies a run timeout in seconds. fs_usage will run for no
longer than the timeout specified.
Specifies a raw trace file to process.
If -R is selected, specifies the start time in microseconds to
begin processing entries from the raw trace file. Entries with
timestamps before the specified start time will be skipped.
If -R is selected, specifies the ending time in microseconds to
stop processing entries from the raw trace file. Entries with
timestamps beyond the specified ending time will be skipped.
pid | cmd
The sampled data can be limited to a list of process IDs or
commands. When a command name is given, all processes with that
name will be sampled. Using the -e option has the opposite effect,
excluding sampled data relating to the given list of process IDs or
The data columns displayed are as follows:
TOD when call occurred. Wide mode will have microsecond
CALL The name of the network or filesystem related call, page-in, page-
out, or physical disk access.
Of the form F=x, x is a file descriptor. Depending on the type of
system call, this will be either an input value or a return value.
Of the form B=x, x is the number of bytes requested by the call.
On error, the errno is displayed in brackets.
Pathname of the file accessed (up to the last 28 bytes).
Of the form A=0xnnnnnnnn, where 0xnnnnnnnn is the address being
DISK BLOCK NUMBER
Of the form D=0xnnnnnnnn, where 0xnnnnnnnn is the block number of
the physical disk block being read or written.
OFFSET Of the form O=0xnnnnnnnn, where 0xnnnnnnnn is a file offset.
Of the form S=x, x is the number of ready descriptors returned by
the select(2) system call. If S=0, the time limit expired.
The elapsed time spent in the system call. A ‘W’ after the elapsed
time indicates the process was scheduled out during this file
activity. In this case, the elapsed time includes the wait time.
The process that made the system call. Wide mode will append the
thread id to the process name (i.e Mail.nnn).
fs_usage -w -f filesys Mail fs_usage will display file system related data
for all instances of processes named Mail. Maximum data output will be
displayed in the window.
dyld(1), latency(1), sc_usage(1), top(1)
macOS November 7, 2002 macOS