NAME¶
mbuffer - measuring buffer
SYNTAX¶
mbuffer [
options]
DESCRIPTION¶
mbuffer buffers I/O operations and displays the throughput rate. It is
multi-threaded, supports network connections, and offers more options than the
standard buffer.
OPTIONS¶
- -i <filename>
- Use filename as input instead of the standard input (needs to be
given for multi volume support). If filename is -, input is read
from standard input.
- -I <port>
- Use network port port as input instead of the standard input. If
given a hostname and a port in the form hostname:port, the first interface
with the IP of hostname will be used.
- -o <filename>
- Use filename as output instead of the standard output (needs to be
given for multi volume support, will enable use of sendfile if available).
If filename is -, output is written to standard output. The option
-o can be passed multiple times to specify multiple outputs.
- -O <hostname:port>
- Write output to hostname:port instead of the standard output (will
enable use of sendfile if available). This option can be used multiple
times to send data to multiple machines.
- -b <num>
- Use num blocks for buffer (default 256).
- -s <size>
- Use blocks of size bytes for buffer (default pagesize of
system).
- -m <size>
- Use a total of size bytes for buffer (default 2MB) - size can be
set with a trailing character (b and B for Byte, k for kByte, M for MByte,
G for Gigabyte, and with % for a percentage of total physical
memory).
- -L
- Lock buffer in memory - this option is not available for file-based
buffers and requires mbuffer to be set-UID root (use with care).
- -n <num>
- num volumes in input device (requires use of option -i for input
device specification, pass 0 as argument if mbuffer should prompt for
every new volume)
- -t
- use a memory-mapped temporary file as buffer (use with huge buffers)
- -T <file>
- as -t but use file instead
- -d
- use block-size of device for output (needed for some devices, slows output
down)
- -D <size>
- assume an output volume of size bytes (default infinite) after
which a volume change will be initiated. Small values are useful for the
timely testing of multi-volume runs; accurate values if your device
doesn't properly signal end of media. Size can be set with a trailing
character (b and B for Byte, k for kByte, M for MByte, or G for
Gigabyte)
- -P <num>
- start writing after the buffer has been filled to num% (default 0 -
start at once)
- -p <num>
- start reading after the buffer has dropped below fill-ratio of num%
(default 100 - start at once)
- -l <file>
- log messages to file instead of standard error output
- -u <num>
- pause num microseconds after each write - might increase
performance on some drives with very low performance (< 1 MB/sec)
- -r <rate>
- Set the maximum read rate to <rate>. <rate> can
be given in either Bytes, kBytes, MBytes, or GBytes per second. To do so,
use an appropriate suffix (i.e. k,M,G). This option is useful if you have
a tape that is capable of transferring data faster than the host can
handle it. In this case you can use this option to limit the transfer rate
and keep the tape running. Be aware that this is both good for your tape
drive, and enhances overall performance, by avoiding tape screwing.
- -R <rate>
- Same as above only for setting the transfer limit for the writer.
- -A <cmd>
- the device used is an autoloader which uses cmd to load the next
volume. Pass < /bin/false> as an autoload command to suppress
the warning message that appears when run without controlling terminal
(e.g. via cron). Like this the autoload will fail and mbuffer will
terminate with an error message when reaching the end of the tape.
- -a <time>
- the device used is an autoloader which takes time seconds to load a
new tape
- -f
- overwrite output file if it exists already
- -c
- write with synchronous data integrity support - This option forces all
writes to complete before continuing. This enables errors to be reported
earlier and more precisely, but might decrease performance. Especially
systems with high level of data integrity support suffer a huge
performance hit. Others might seem to be unaffected, but just neglect
support for full synchronous data integrity.
- -v <num>
- set verbose level to num. Valid values are 0..6 (0 = none, 1 =
errors, 2 = warnings, 4 = information messages, 5 = debugging messages, 6
= I/O debugging). Higher values include lower values messages.
- -q
- quiet - do not display the status on the standard error output
- -Q
- quiet - do not log the status in the log file
- --direct
- Use O_DIRECT to open file descriptors. This option is not available on all
systems. It tells the OS to bypass the page cache to improve performance
when reading and writing. On Solaris this is an auto-magic option that is
enabled if it is supported for the relevant file. Be aware that this
option might lead to read/write failures, if the buffer isn't properly
aligned for direct I/O. Additionally, open might fail with EINVAL (i.e.
invalid argument) if the named file does not support O_DIRECT.
- --append
- Open next output file given via option -o in append mode.
- --truncate
- Truncate next output file given via option -o when opening it.
- -6
- Force IPv6 mode for the following network I/O options on command line.
-4 Force IPv4 mode for the following network I/O options on command
line. -0 Choose IPv4/IPv6 mode on demand.
- -h, --help
- Output help information and exit.
- -H, --md5
- Generate a MD5 hash of transferred data.
- -V, --version
- Output version information and exit.
- -W <timeout>
- Activates a watchdog that gets triggered every timeout seconds and
checks weather I/O activity has stalled. If either channel has stalled for
a complete period, the watchdog writes an error message and terminates
mbuffer via SIGINT. Be aware that the watchdog is unaware of tape-change
activities. So choose the watchdog timeout greater that the worst-case
tape-change time.
DEFAULT VALUES¶
The default values for following options can be set as
key = value pairs
in the ~/.mbuffer.rc file:
blocksize: block size (option -s)
timeout: watchdog timeout (option -W)
totalmem: total buffer size (option -m)
maxreadspeed: maximum read speed (option -r)
maxwritespeed: maximum write speed (option -R)
startwrite: threshold for start writing (option -P)
startread: threshold for start reading (option -p)
pause: pause after writing a block (option -u)
numblocks: number of blocks in buffer (option -b)
memlock: lock buffer in memory (option -L)
showstatus: print transfer status on console (option -q)
logstatus: write transfer status to logfile (option -Q)
tcpbuffer: TCP buffer size (option --tcpbuffer)
ENVIRONMENT VARIABLES¶
If TMPDIR is set, mbuffer allocates storage for file-based buffers in this
directory. If TMPDIR is unset,
/var/tmp will be used.
FILES¶
/usr/bin/mbuffer
/var/tmp/mbuffer-*
~/.mbuffer.rc
EXAMPLES¶
To run this program with the default options just type:
mbuffer
Using mbuffer to do a backup with tar to the default tape device. Options for
this example: memory-mapped temporary file with a size of 10 Megabytes, start
after 80% of the buffer have been filled.
tar cf - mydirectory | gzip | mbuffer -t -m 10M -P 80 -f -o $TAPE
Using mbuffer with 3 tapes for input and extracting the contents in the current
work directory:
mbuffer -n 3 -i $TAPE | gzip -dc | tar xf -
Using mbuffer to write to multiple tape volumes:
tar cf - /usr | mbuffer -f -o $TAPE
Write to multiple tapes and erase every tape before writing:
tar cf - /usr | mbuffer -A "echo next tape; read a < /dev/tty; mt erase
$TAPE" -f -o $TAPE
Making a backup via network:
tape server: mbuffer -I 8000 -f -o $TAPE
backup client: tar zcf - /home | mbuffer -O tapeserver:8000
Distributing a directory tree to multiple machines:
master: tar cf - /tree_to_clone | mbuffer -O clone0:8000 -O clone1:8000
clones: mbuffer -I master:8000 | tar xf -
EXITCODE¶
mbuffer return 0 upon success. Any kind of failure will yield a non-zero exit
code.
AUTHORS¶
Thomas Maier-Komor <thomas@maier-komor.de>
DONATIONS¶
If you like this software, and use it for production purposes in your company,
please consider making a donation to support this work. You can donate
directly via PayPal to the author's e-mail address (thomas@maier-komor.de).
HOMEPAGE¶
http://www.maier-komor.de/mbuffer.html
LICENSE¶
This software is published under GNU General Public License V3. See file LICENSE
for details.
SEE ALSO¶
buffer(1)