NAME

       pipesz - set or examine pipe and FIFO buffer sizes

SYNOPSIS

       pipesz [options] [--set size] [--] [command [argument] ...]

       pipesz [options] --get

DESCRIPTION

       Pipes and FIFOs maintain an internal buffer used to transfer data between the read end and the write end.
       In some cases, the default size of this internal buffer may not be appropriate. This program provides
       facilities to set and examine the size of these buffers.

       The --set operation sets pipe buffer sizes. If it is specified, it must be specified with an explicit
       size. Otherwise, it is implied and the size is read from /proc/sys/fs/pipe-max-size. The kernel may
       adjust size as described in fcntl(2). To determine the actual buffer sizes set, use the --verbose option.
       If neither --file nor --fd are specified, --set acts on standard output.

       The --set operation permits an optional command to execute after setting the pipe buffer sizes. This
       command is executed with the adjusted pipes.

       The --get operation outputs data in a tabular format. The first column is the name of the pipe as passed
       to pipesz. File descriptors are named as "fd N". The second column is the size, in bytes, of the pipe’s
       internal buffer. The third column is the number of unread bytes currently in the pipe. The columns are
       separated by tabs ('\t', ASCII 09h). If --verbose is specified, a descriptive header is also emitted. If
       neither --file nor --fd are specified, --get acts on standard input.

       Unless the --check option is specified, pipesz does not exit if it encounters an error while manipulating
       a file or file descriptor. This allows pipesz to be used generically without fear of disrupting the
       execution of pipelines should the type of certain files be later changed. For minimal disruption, the
       --quiet option prevents warnings from being emitted in these cases.

       The kernel imposes limits on the amount of pipe buffer space unprivileged processes can use, though see
       BUGS below. The kernel will also refuse to shrink a pipe buffer if this would cause a loss of buffered
       data. See pipe(7) for additional details.

       pipesz supports specifying multiple short options consecutively, in the usual getopt(3) fashion. The
       first non-option argument is interpreted as command. If command might begin with '-', use '--' to
       separate it from arguments to pipesz. In shell scripts, it is good practice to use '--' when parameter
       expansion is involved. pipesz itself does not read from standard input and does not write to standard
       output unless --get, --help, or --version are specified.

OPTIONS

       -g, --get
           Report the size of pipe buffers to standard output and exit. As a special behavior, if neither --file
           nor --fd are specified, standard input is examined. It is an error to specify this option in
           combination with --set.

       -s, --set size
           Set the size of the pipe buffers, in bytes. This option may be suffixed by K, M, G, KiB, MiB, or GiB
           to indicate multiples of 1024. Fractional values are supported in this case. Additional suffixes are
           supported but are unlikely to be useful. If this option is not specified, a default value is used, as
           described above. If this option is specified multiple times, a warning is emitted and only the
           last-specified size is used. As a special behavior, if neither --file nor --fd are specified,
           standard output is adjusted. It is an error to specify this option in combination with --get.

       -f, --file path
           Set the buffer size of the FIFO or pipe at path, relative to the current working directory. You may
           specify this option multiple times to affect different files, and you may do so in combination with
           --fd. Generally, this option is used with FIFOs, but it will also operate on anonymous pipes such as
           those found in /proc/PID/fd. Changes to the buffer size of FIFOs are not preserved across system
           restarts.

       -n, --fd fd
           Set the buffer size of the pipe or FIFO passed to pipesz as the specified file descriptor number. You
           may specify this option multiple times to affect different file descriptors, and you may do so in
           combination with --file. Shorthand options are provided for the common cases of fd 0 (stdin), fd 1
           (stdout), and fd 2 (stderr). These should suffice in most cases.

       -i, --stdin
           Shorthand for --fd 0.

       -o, --stdout
           Shorthand for --fd 1.

       -e, --stderr
           Shorthand for --fd 2.

       -c, --check
           Exit, without executing command, in case of any error while manipulating a file or file descriptor.
           The default behavior if this is not specified is to emit a warning to standard error and continue.

       -q, --quiet
           Do not diagnose non-fatal errors to standard error. This option does not affect the normal output of
           --get, --verbose, --help, or --version.

       -v, --verbose
           If specified with --get, pipesz will emit a descriptive header above the table. Otherwise, if
           specified, pipesz will print the actual buffer sizes set by the kernel to standard error.

       -h, --help
           Display help text and exit.

       -V, --version
           Print version and exit.

EXAMPLES

       pipesz dd if=file bs=1M | ...
           Runs dd(1) with an expanded standard output pipe, allowing it to avoid context switches when piping
           around large blocks.

       pipesz -s1M -cf /run/my-service.fifo
           Sets the pipe buffer size of a service FIFO to 1,048,576 bytes. If the buffer size could not be set,
           pipesz exits with an error.

       echo hello | pipesz -g
           Prints the size of pipe used by the shell to pass input to pipesz. Since pipesz does not read
           standard input, it may also report 6 unread bytes in the pipe, depending on relative timings.

       find /proc/PID/fd -exec pipesz -gqf '{}' ';'
           Prints the size and number of unread bytes of all pipes in use by PID. If some pipes are routinely
           full, pipesz might be able to mitigate a processing bottleneck.

NOTES

       Linux supports adjusting the size of pipe buffers since kernel 2.6.35. This release also introduced
       /proc/sys/fs/pipe-max-size.

       This program uses fcntl(2) F_GETPIPE_SZ/F_SETPIPE_SZ to get and set pipe buffer sizes.

       This program uses ioctl(2) FIONREAD to report the amount of unread data in pipes. If for some reason this
       fails, the amount of unread data is reported as 0.

BUGS

       Before Linux 4.9, some bugs affect how certain resource limits are enforced when setting pipe buffer
       sizes. See pipe(7) for details.

AUTHORS

       Nathan Sharp <nwsharp@live.com>

SEE ALSO

       pipe(7)

REPORTING BUGS

       For bug reports, use the issue tracker at https://github.com/util-linux/util-linux/issues.

AVAILABILITY

       The pipesz command is part of the util-linux package which can be downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.39.3                                  2023-11-21                                          PIPESZ(1)