/etc/pipestat [ -n namelist ] [ -t timestep ]
A pipe is a first-in first-out (FIFO) data structure used to transfer the output of one program to the input of another.
The data structures associated with UNIX System V (S5) and XENIX filesystem pipes are normally stored in the buffer cache and accessed via inodes, like regular files. They notionally reside on filesystems which must be mounted and both readable and writable; otherwise such pipes cannot be used. The pipes borrow inodes from this filesystem, but will not write data to the physical medium except under exceptional circumstances.
The High Performance Pipe System (HPPS) implements its pipes entirely within the kernel. The pipe inode never exists on any physical device, and data transfer via the buffer cache is not used. Typically, throughput of HPPS pipes is about twice that of S5 pipes.
Pipes to be opened are obtained from the topmost pipe filesystem on the stack. If no pipes are available, the request to open a pipe drops down the stack to try the next available pipe filesystem.
pipe takes the following options:
pipestat returns information about the usage of the HPPS. The statistics are totals since the HPPS was initialized. The output columns are:
hppsif an HPPS pipe,
otherfor a filesystem-based pipe
If you specify a time interval timestep in seconds
using the -t option,
pipestat returns the statistics for the
opened, fail, r, w, ww, and
bytes columns as per
/s) averages over the time interval.
The default namelist kernel binary is /unix.
If you booted a different version of the kernel (such as
unix.old), you must specify it using the -n option:
/etc/pipestat -n unix.old
Programs attempting to create, write to, or read from a pipe will experience an error condition if no writable or readable pipe filesystem is available.
Named pipes (FIFOs) reside on the filesystem containing their name, and do not use the pipe filesystem.
There is no support for named pipes in the High Performance Pipe System.
Each high performance pipe requires 8KB of memory while it is open.