||FreeBSD General Commands Manual
direct data streams, with bandwidth limiting, FIFO, audio,
duplication and extended reporting support.
Cstream filters data streams, much like the UNIX tool
dd(1). It has
a more traditional commandline syntax, support for precise bandwidth limiting
and reporting and support for FIFOs. Data limits and throughput rate
calculation will work for files > 4 GB.
Cstream reads from the standard input and
writes to the standard output, if no filenames are given. It will also
'generate' or 'sink' data if desired.
- Set the block size used for read/write to num. The
default is 8192 bytes.
- Buffer input up to num bytes before writing. The
default is the blocksize. It is an error to set this to anything below the
blocksize. Useful when writing tapes and similar that prefer few large
writes of many small.
- Concurrent operation. Use a separate process for output. This is
especially useful in combination with the -B option.
- 0 = use one process only (default)
- 1 = read process will buffer
- 2 = write process will buffer
- 3 = both processes will buffer.
- In combination with a large buffer size this will often load your
memory heavily, every time the reader transfers the buffer it
collected to the writer. If you use -c 3 and have a buffer size of 128
Megabytes 256 MB of memory will be touched at once.
- Set the file names to use for input or output, respectively. If the output
file name is "-", data will just be discarded. If the input file
name is "-", data will be generated 'out of the void'. If these
options aren't given, stdin/stout will be used. If you need to give
-i options and want
stdin/stdout, specify the empty string, like this:
If TCP support has been compiled in (default),
hostname:portnumber will try to connect to the specified host at the
specified port and :portnumber will open a TCP socket on the local
machine and wait for a connection to arrive. SECURITY NOTE: cstream
includes no mechanism to restrict the hosts that may connect to this
port. Unless your machine has other network filters, anyone will be able
- Specify the type of input and output file, respectively.
- If string
- includes 'f', a fifo will be created.
- If string
- includes 'F', a rsync(2) will be issued before closing the output
- If string
- includes 'a', the file will be assumed to be a opensound-compatible
audio device and will be switched to CD-like settings.
- If string
- includes 't', a copy of the stream will be sent to file descriptor
- If string
- includes 'N', TCP will not be used for that file even if the name has
- Include line count in statistics.
- Limit the total amount of data to num. If there is
more input available, it will be discarded,
cstream will exit after the limit has been
reached. If there is less input, the limit will not be reached and no
error will be signaled.
num may have a trailing 'k', 'm' or 'g'
which means Kilobytes, Megabytes or Gigabytes (where Kilo = 1024). This
applies to all numeric options.
- Write the process id of cstream to filename. If
cstream uses a separate writer process (option -c), this is the pid of the
parent (reader) process.
- Limit the throughput of the data stream to num
bytes/second. Limiting is done at the input side, you can rely on cstream
not accepting more than this rate. If the number you give is positive,
cstream accumulates errors and tries to keep the overall rate at the
specified value, for the whole session. If you give a negative number, it
is an upper limit for each read/write system call pair. In other words:
the negative number will never exceed that limit, the positive number will
exceed it to make good for previous underutilization.
- Report throughput every num seconds.
- Set verbose level to num. By default, it is set to
0, which means no messages are displayed as long as no errors occur. A
value of 1 means that total amount of data and throughput will be
displayed at the end of program run. A value of 2 means the transfer rate
since the end of the first read/write pair will also be reported (useful
when there is an initial delay). A value of 3 means there will also be
separate measurements for read and write. This option is
resource-consuming and currently isn't implemented. A value of 4 means
that notices about each single read/write will be displayed. High values
include all message types of lower values.
- Print version number to stdout and exit with 0.
- A single filename as the last argument without an option switch will be
used as input file if -i has not been used.
- Sending SIGUSR1 (or SIGINFO, which is usually mapped to Control-T on you
keyboard) to cstream causes it to display throughput rates to stderr. The
stream will continue as if nothing happened.
- Exit and report throughput rates, if requested.
- I found myself sending SIGHUP accidentally too often. But ignoring or
misusing SIGHUP is not an option for me. Thus, when
cstream received SIGHUP, it will wait 5 seconds
for another SIGHUP, to give users a chance to correct a possible mistake.
If no additional SIGHUP is received,
itself with SIGHUP.
-o tmpfile -v 1 -n 384m -i -
- Writes 384 Megabytes of unspecified data to file
tmpfile and display verbose throughput rate. Makes
a good benchmark, the speed of /dev/null varies
too much from system to system.
-i tmpfile -v 1 -n 384m -o -
- Read the same file back in and discard data.
-b 2000 -t 10000 /var/log/messages
- Will display the file in a more or less watchable speed.
0sf 400000 - / | cstream -v 1 -b 32768 -o /dev/rst0 -p
-USR1 `cat pidfile`
- Write the output from dump(1) to tape. Each time the signal is sent, the
throughput and data rate so far will be displayed.
-t 176400 -i /dev/dsp0 -I f -o -
- Makes kind of a soundcard emulator which may be used to test audio
applications that need something to write to that limits the data rate as
a real soundcard does. This obviously doesn't work when the application
tries to write data using mmap(2) and the application has to ignore errors
when it tries to set soundcard parameters using ioctl(2).
-t 176400 -i /dev/dsp0 -I f -o /dev/dsp1 -O f
- Similar soundcard emulator, except that it allows you to grab the data
your applications sends to it from the other fifo, while still having
-Oa -o /dev/dsp0 myhost.mydomain.com:17324
- Connects port 3333 on host myhost.mydomain.com and whatever data it finds
there will be sent to the soundcard, with appropriate settings for CD
quality stereo play.
-i myaudiofile.raw -o :17324
- This will open a TCP server on port 17324 and waits until someone connects
(for example, the commandline from the previous example). Then it will
send the contents of myaudiofile.raw down the TCP stream (for the previous
audio example, typically a CD audio track like you get from the tosha or
-OD -o myfile
- Write to file myfile with O_DIRECT. That usually means that the filesystem
buffer cache will not try to cache this file. You can use that to prevent
copying operations from eating up physical memory. Note that when cstream
encounters a write error it will switch the output file from O_DIRECT to a
normal file and write all further blocks without O_DIRECT if writes
without O_DIRECT succeed. In practice that usually means that your last
block, if not a multiple of the filesystem block size, will still be
written into the file (the maximum amount of data written without O_DIRECT
is your blocksize minus one). That way cstream ensures that the output
file has the length of the input, however odd the length was and no matter
what restrictions your OS places on O_DIRECT output. Again, cstream will
*not* pad the output to the block size, you get the same file and file
size as if not using O_DIRECT, at the cost of switching to non-O_DIRECT
whenever a block is not the right size.
-i :3333 |
-omyfile -v7 -OD
- This is what you need to do to buffer TCP input, so that the last cstream
will not switch away from O_DIRECT prematurely because of short reads. If
your input can do short reads (e.g. from TCP), and you want to ensure that
O_DIRECT stays in effect, you need a buffer between the TCP stream and the
O_DIRECT stream. Since cstream does not yet support different input and
output block sizes, dd is suitable here. Note that this is only necessary
if the OS requires multiples of the filesystem block size for O_DIRECT. At
the time of this writing this construct is needed on Linux for using TCP
streams with O_DIRECT, but it is not needed on FreeBSD.
-OS -o myfile
- Writes to file myfile with O_SYNC. This means by the time the system call
returns the data is known to be on disk. This is not the same thing as
O_DIRECT. O_DIRECT can do its own buffering, with O_SYNC there is no
buffering at all. At the time of this writing, O_SYNC on both Linux and
FreeBSD is very slow (1/5th to 1/10th of normal write) and O_DIRECT is
reasonably fast (1/4th to 1/2 of normal write). You can combined O_SYNC
There should be an option to begin writing directly after the first read ended
and then fill the buffer with reads in the background. Right now writing will
not begin before the reader has filled the buffer completely for the first
- Exit code 0 means success.
- Exit code 1 means a commandline syntax usage error.
- Exit code 2 means other errors, especially system errors.
Not a bug: the code to do O_DIRECT is reasonably sophisticated. It
will fall back to normal I/O on errors. But before doing that it knows about
both filesystem blocksize requirements (will default I/O blocksize to
whatever the filesystem of the output file is in) and page alignment
requirements (I/O will happen from a page-aligned buffer). However, the
combination of concurrent read/writes (-c options) and O_DIRECT has not been
tested beyond basic verification that it gets some tests right.
cstream was initially written by Martin Cracauer in
1998. For updates and more information see
Visit the GSP FreeBSD Man Page Interface.
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