FS_USAGE(1) BSD General Commands Manual FS_USAGE(1)NAMEfs_usage — report system calls and page faults related to filesystem
activity in real-time
SYNOPSISfs_usage [-e] [-w] [-f mode] [pid|cmd [pid|cmd] ...]
The fs_usage utility presents an ongoing display of system call usage
information pertaining to filesystem activity. It requires root privi‐
leges 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, sshd, rlogind, tcsh, csh and sh.
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 for‐
matting restrictions by forcing a wide display with the -w option. In
this case, the data displayed will wrap when the window is not wide
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 com‐
mands is also given, then those processes are also excluded from
the sampled output.
-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. By default no filtering occurs. The supported
network Only network related output is displayed.
filesys Only file system related output is displayed.
pid | cmd
The sampled data can be limited to a list of process ids or com‐
mands. 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 commands.
If you set the DYLD_IMAGE_SUFFIX environment variable to “_debug”, then
an application will use the debug version of all libraries including the
Carbon FileManager. See dyld(1). When fs_usage is run against a Carbon
Application launched in this environment, then the high level Carbon
FileManager calls will be displayed bracketing the system calls that they
are built on.
The data columns displayed are as follows:
TOD when call occurred. Wide mode will have millisecond granu‐
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
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() 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
The process that made the system call.
SAMPLE USAGEfs_usage-w -f filesys Mail
fs_usage will display file system related data for all instances of pro‐
cesses named Mail. Maximum data output will be displayed in the window.
SEE ALSOtop(1), sc_usage(1), latency(1), dyld(1)Mac OS X November 7, 2002 Mac OS X