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cstream — direct data streams, with bandwidth limiting, FIFO, audio, duplication and
extended reporting support.


cstream [-b num] [-B num] [-i filename] [-I string] [-l] [-n num] [-o filename] [-O string]
[-p filename] [-t num] [-T num] [-v num] [-V] [filename]


Cstream filters data streams, much like the UNIX tool dd(1). It has a more traditional
command line 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.


-b num Set the block size used for read/write to num. The default is 8192 bytes.

-B num 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.

-c num 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.

-i num

-o num 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 -o or -i options and want stdin/stdout, specify the
empty string, like this:

cstream -i''

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 to

-I string

-O string
Specify the type of input and output file, respectively.
If string
includes 'f', a fifo will be created.
If string
includes 'a', the file will be assumed to be an 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 3.
If string
includes 'N', TCP will not be used for that file even if the name has a ":".

-l Include line count in statistics.

-n num 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.

-p filename
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.

-t num 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.

-T num Report throughput every num seconds.

-v num 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

-V Print version number to stdout and exit with 0.

filename A single filename as the last argument without an option switch will be used as
input file if -i has not been used.


SIGINFO 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.

SIGUSR2 Exit and report throughput rates, if requested.

SIGHUP 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, cstream kills itself with SIGHUP.


cstream -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.

cstream -i tmpfile -v 1 -n 384m -o -
Read the same file back in and discard data.

cstream -b 2000 -t 10000 /var/log/messages
Will display the file in a more or less watchable speed.

dump 0sf 400000 - / | cstream -v 1 -b 32768 -o /dev/rst0 -p pidfile

kill -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.

cstream -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

cstream -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 precise timing.

cstream -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 stero play.

cstream -i myaudiofile.raw -o :17324
This will open a TCP server on port 17324 and waits until someone connects (for
example, the command line 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 audiotrack like you get from the tosha or cdparanoia utilities).

cstream -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

cstream -i :3333 | dd obs=8192 | ./cstream -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.

cstream -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 and O_DIRECT.


Exit code 0 means success.

Exit code 1 means a command line syntax usage error.

Exit code 2 means other errors, especially system errors.


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 time.

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.

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