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).

     -t seconds
             Specifies a run timeout in seconds.  fs_usage will run for no
             longer than the timeout specified.

     -R raw_file
             Specifies a raw trace file to process.

     -S start_time
             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.

     -E end_time
             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

             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